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//===- CodeGenPrepare.cpp - Prepare a function for code generation --------===//
// The LLVM Compiler Infrastructure
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
// This pass munges the code in the input function to better prepare it for
// SelectionDAG-based code generation. This works around limitations in it's
// basic-block-at-a-time approach. It should eventually be removed.
#include "llvm/ADT/APInt.h"
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/PointerIntPair.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/BlockFrequencyInfo.h"
#include "llvm/Analysis/BranchProbabilityInfo.h"
#include "llvm/Analysis/ConstantFolding.h"
#include "llvm/Analysis/InstructionSimplify.h"
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/Analysis/MemoryBuiltins.h"
#include "llvm/Analysis/ProfileSummaryInfo.h"
#include "llvm/Analysis/TargetLibraryInfo.h"
#include "llvm/Analysis/TargetTransformInfo.h"
#include "llvm/Transforms/Utils/Local.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/CodeGen/Analysis.h"
#include "llvm/CodeGen/ISDOpcodes.h"
#include "llvm/CodeGen/SelectionDAGNodes.h"
#include "llvm/CodeGen/TargetLowering.h"
#include "llvm/CodeGen/TargetPassConfig.h"
#include "llvm/CodeGen/TargetSubtargetInfo.h"
#include "llvm/CodeGen/ValueTypes.h"
#include "llvm/Config/llvm-config.h"
#include "llvm/IR/Argument.h"
#include "llvm/IR/Attributes.h"
#include "llvm/IR/BasicBlock.h"
#include "llvm/IR/CallSite.h"
#include "llvm/IR/Constant.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/DerivedTypes.h"
#include "llvm/IR/Dominators.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/GetElementPtrTypeIterator.h"
#include "llvm/IR/GlobalValue.h"
#include "llvm/IR/GlobalVariable.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/InlineAsm.h"
#include "llvm/IR/InstrTypes.h"
#include "llvm/IR/Instruction.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/Intrinsics.h"
#include "llvm/IR/LLVMContext.h"
#include "llvm/IR/MDBuilder.h"
#include "llvm/IR/Module.h"
#include "llvm/IR/Operator.h"
#include "llvm/IR/PatternMatch.h"
#include "llvm/IR/Statepoint.h"
#include "llvm/IR/Type.h"
#include "llvm/IR/Use.h"
#include "llvm/IR/User.h"
#include "llvm/IR/Value.h"
#include "llvm/IR/ValueHandle.h"
#include "llvm/IR/ValueMap.h"
#include "llvm/Pass.h"
#include "llvm/Support/BlockFrequency.h"
#include "llvm/Support/BranchProbability.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/MachineValueType.h"
#include "llvm/Support/MathExtras.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Target/TargetOptions.h"
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
#include "llvm/Transforms/Utils/BypassSlowDivision.h"
#include "llvm/Transforms/Utils/SimplifyLibCalls.h"
#include <algorithm>
#include <cassert>
#include <cstdint>
#include <iterator>
#include <limits>
#include <memory>
#include <utility>
#include <vector>
using namespace llvm;
using namespace llvm::PatternMatch;
#define DEBUG_TYPE "codegenprepare"
STATISTIC(NumBlocksElim, "Number of blocks eliminated");
STATISTIC(NumPHIsElim, "Number of trivial PHIs eliminated");
STATISTIC(NumGEPsElim, "Number of GEPs converted to casts");
STATISTIC(NumCmpUses, "Number of uses of Cmp expressions replaced with uses of "
"sunken Cmps");
STATISTIC(NumCastUses, "Number of uses of Cast expressions replaced with uses "
"of sunken Casts");
STATISTIC(NumMemoryInsts, "Number of memory instructions whose address "
"computations were sunk");
"Number of phis created when address "
"computations were sunk to memory instructions");
"Number of select created when address "
"computations were sunk to memory instructions");
STATISTIC(NumExtsMoved, "Number of [s|z]ext instructions combined with loads");
STATISTIC(NumExtUses, "Number of uses of [s|z]ext instructions optimized");
"Number of and mask instructions added to form ext loads");
STATISTIC(NumAndUses, "Number of uses of and mask instructions optimized");
STATISTIC(NumRetsDup, "Number of return instructions duplicated");
STATISTIC(NumDbgValueMoved, "Number of debug value instructions moved");
STATISTIC(NumSelectsExpanded, "Number of selects turned into branches");
STATISTIC(NumStoreExtractExposed, "Number of store(extractelement) exposed");
static cl::opt<bool> DisableBranchOpts(
"disable-cgp-branch-opts", cl::Hidden, cl::init(false),
cl::desc("Disable branch optimizations in CodeGenPrepare"));
static cl::opt<bool>
DisableGCOpts("disable-cgp-gc-opts", cl::Hidden, cl::init(false),
cl::desc("Disable GC optimizations in CodeGenPrepare"));
static cl::opt<bool> DisableSelectToBranch(
"disable-cgp-select2branch", cl::Hidden, cl::init(false),
cl::desc("Disable select to branch conversion."));
static cl::opt<bool> AddrSinkUsingGEPs(
"addr-sink-using-gep", cl::Hidden, cl::init(true),
cl::desc("Address sinking in CGP using GEPs."));
static cl::opt<bool> EnableAndCmpSinking(
"enable-andcmp-sinking", cl::Hidden, cl::init(true),
cl::desc("Enable sinkinig and/cmp into branches."));
static cl::opt<bool> DisableStoreExtract(
"disable-cgp-store-extract", cl::Hidden, cl::init(false),
cl::desc("Disable store(extract) optimizations in CodeGenPrepare"));
static cl::opt<bool> StressStoreExtract(
"stress-cgp-store-extract", cl::Hidden, cl::init(false),
cl::desc("Stress test store(extract) optimizations in CodeGenPrepare"));
static cl::opt<bool> DisableExtLdPromotion(
"disable-cgp-ext-ld-promotion", cl::Hidden, cl::init(false),
cl::desc("Disable ext(promotable(ld)) -> promoted(ext(ld)) optimization in "
static cl::opt<bool> StressExtLdPromotion(
"stress-cgp-ext-ld-promotion", cl::Hidden, cl::init(false),
cl::desc("Stress test ext(promotable(ld)) -> promoted(ext(ld)) "
"optimization in CodeGenPrepare"));
static cl::opt<bool> DisablePreheaderProtect(
"disable-preheader-prot", cl::Hidden, cl::init(false),
cl::desc("Disable protection against removing loop preheaders"));
static cl::opt<bool> ProfileGuidedSectionPrefix(
"profile-guided-section-prefix", cl::Hidden, cl::init(true), cl::ZeroOrMore,
cl::desc("Use profile info to add section prefix for hot/cold functions"));
static cl::opt<unsigned> FreqRatioToSkipMerge(
"cgp-freq-ratio-to-skip-merge", cl::Hidden, cl::init(2),
cl::desc("Skip merging empty blocks if (frequency of empty block) / "
"(frequency of destination block) is greater than this ratio"));
static cl::opt<bool> ForceSplitStore(
"force-split-store", cl::Hidden, cl::init(false),
cl::desc("Force store splitting no matter what the target query says."));
static cl::opt<bool>
EnableTypePromotionMerge("cgp-type-promotion-merge", cl::Hidden,
cl::desc("Enable merging of redundant sexts when one is dominating"
" the other."), cl::init(true));
static cl::opt<bool> DisableComplexAddrModes(
"disable-complex-addr-modes", cl::Hidden, cl::init(false),
cl::desc("Disables combining addressing modes with different parts "
"in optimizeMemoryInst."));
static cl::opt<bool>
AddrSinkNewPhis("addr-sink-new-phis", cl::Hidden, cl::init(false),
cl::desc("Allow creation of Phis in Address sinking."));
static cl::opt<bool>
AddrSinkNewSelects("addr-sink-new-select", cl::Hidden, cl::init(true),
cl::desc("Allow creation of selects in Address sinking."));
static cl::opt<bool> AddrSinkCombineBaseReg(
"addr-sink-combine-base-reg", cl::Hidden, cl::init(true),
cl::desc("Allow combining of BaseReg field in Address sinking."));
static cl::opt<bool> AddrSinkCombineBaseGV(
"addr-sink-combine-base-gv", cl::Hidden, cl::init(true),
cl::desc("Allow combining of BaseGV field in Address sinking."));
static cl::opt<bool> AddrSinkCombineBaseOffs(
"addr-sink-combine-base-offs", cl::Hidden, cl::init(true),
cl::desc("Allow combining of BaseOffs field in Address sinking."));
static cl::opt<bool> AddrSinkCombineScaledReg(
"addr-sink-combine-scaled-reg", cl::Hidden, cl::init(true),
cl::desc("Allow combining of ScaledReg field in Address sinking."));
static cl::opt<bool>
EnableGEPOffsetSplit("cgp-split-large-offset-gep", cl::Hidden,
cl::desc("Enable splitting large offset of GEP."));
namespace {
enum ExtType {
ZeroExtension, // Zero extension has been seen.
SignExtension, // Sign extension has been seen.
BothExtension // This extension type is used if we saw sext after
// ZeroExtension had been set, or if we saw zext after
// SignExtension had been set. It makes the type
// information of a promoted instruction invalid.
using SetOfInstrs = SmallPtrSet<Instruction *, 16>;
using TypeIsSExt = PointerIntPair<Type *, 2, ExtType>;
using InstrToOrigTy = DenseMap<Instruction *, TypeIsSExt>;
using SExts = SmallVector<Instruction *, 16>;
using ValueToSExts = DenseMap<Value *, SExts>;
class TypePromotionTransaction;
class CodeGenPrepare : public FunctionPass {
const TargetMachine *TM = nullptr;
const TargetSubtargetInfo *SubtargetInfo;
const TargetLowering *TLI = nullptr;
const TargetRegisterInfo *TRI;
const TargetTransformInfo *TTI = nullptr;
const TargetLibraryInfo *TLInfo;
const LoopInfo *LI;
std::unique_ptr<BlockFrequencyInfo> BFI;
std::unique_ptr<BranchProbabilityInfo> BPI;
/// As we scan instructions optimizing them, this is the next instruction
/// to optimize. Transforms that can invalidate this should update it.
BasicBlock::iterator CurInstIterator;
/// Keeps track of non-local addresses that have been sunk into a block.
/// This allows us to avoid inserting duplicate code for blocks with
/// multiple load/stores of the same address. The usage of WeakTrackingVH
/// enables SunkAddrs to be treated as a cache whose entries can be
/// invalidated if a sunken address computation has been erased.
ValueMap<Value*, WeakTrackingVH> SunkAddrs;
/// Keeps track of all instructions inserted for the current function.
SetOfInstrs InsertedInsts;
/// Keeps track of the type of the related instruction before their
/// promotion for the current function.
InstrToOrigTy PromotedInsts;
/// Keep track of instructions removed during promotion.
SetOfInstrs RemovedInsts;
/// Keep track of sext chains based on their initial value.
DenseMap<Value *, Instruction *> SeenChainsForSExt;
/// Keep track of GEPs accessing the same data structures such as structs or
/// arrays that are candidates to be split later because of their large
/// size.
SmallVector<std::pair<AssertingVH<GetElementPtrInst>, int64_t>, 32>>
/// Keep track of new GEP base after splitting the GEPs having large offset.
SmallSet<AssertingVH<Value>, 2> NewGEPBases;
/// Map serial numbers to Large offset GEPs.
DenseMap<AssertingVH<GetElementPtrInst>, int> LargeOffsetGEPID;
/// Keep track of SExt promoted.
ValueToSExts ValToSExtendedUses;
/// True if CFG is modified in any way.
bool ModifiedDT;
/// True if optimizing for size.
bool OptSize;
/// DataLayout for the Function being processed.
const DataLayout *DL = nullptr;
static char ID; // Pass identification, replacement for typeid
CodeGenPrepare() : FunctionPass(ID) {
bool runOnFunction(Function &F) override;
StringRef getPassName() const override { return "CodeGen Prepare"; }
void getAnalysisUsage(AnalysisUsage &AU) const override {
// FIXME: When we can selectively preserve passes, preserve the domtree.
bool eliminateFallThrough(Function &F);
bool eliminateMostlyEmptyBlocks(Function &F);
BasicBlock *findDestBlockOfMergeableEmptyBlock(BasicBlock *BB);
bool canMergeBlocks(const BasicBlock *BB, const BasicBlock *DestBB) const;
void eliminateMostlyEmptyBlock(BasicBlock *BB);
bool isMergingEmptyBlockProfitable(BasicBlock *BB, BasicBlock *DestBB,
bool isPreheader);
bool optimizeBlock(BasicBlock &BB, bool &ModifiedDT);
bool optimizeInst(Instruction *I, bool &ModifiedDT);
bool optimizeMemoryInst(Instruction *MemoryInst, Value *Addr,
Type *AccessTy, unsigned AddrSpace);
bool optimizeInlineAsmInst(CallInst *CS);
bool optimizeCallInst(CallInst *CI, bool &ModifiedDT);
bool optimizeExt(Instruction *&I);
bool optimizeExtUses(Instruction *I);
bool optimizeLoadExt(LoadInst *Load);
bool optimizeSelectInst(SelectInst *SI);
bool optimizeShuffleVectorInst(ShuffleVectorInst *SVI);
bool optimizeSwitchInst(SwitchInst *SI);
bool optimizeExtractElementInst(Instruction *Inst);
bool dupRetToEnableTailCallOpts(BasicBlock *BB);
bool placeDbgValues(Function &F);
bool canFormExtLd(const SmallVectorImpl<Instruction *> &MovedExts,
LoadInst *&LI, Instruction *&Inst, bool HasPromoted);
bool tryToPromoteExts(TypePromotionTransaction &TPT,
const SmallVectorImpl<Instruction *> &Exts,
SmallVectorImpl<Instruction *> &ProfitablyMovedExts,
unsigned CreatedInstsCost = 0);
bool mergeSExts(Function &F);
bool splitLargeGEPOffsets();
bool performAddressTypePromotion(
Instruction *&Inst,
bool AllowPromotionWithoutCommonHeader,
bool HasPromoted, TypePromotionTransaction &TPT,
SmallVectorImpl<Instruction *> &SpeculativelyMovedExts);
bool splitBranchCondition(Function &F);
bool simplifyOffsetableRelocate(Instruction &I);
} // end anonymous namespace
char CodeGenPrepare::ID = 0;
"Optimize for code generation", false, false)
"Optimize for code generation", false, false)
FunctionPass *llvm::createCodeGenPreparePass() { return new CodeGenPrepare(); }
bool CodeGenPrepare::runOnFunction(Function &F) {
if (skipFunction(F))
return false;
DL = &F.getParent()->getDataLayout();
bool EverMadeChange = false;
// Clear per function information.
ModifiedDT = false;
if (auto *TPC = getAnalysisIfAvailable<TargetPassConfig>()) {
TM = &TPC->getTM<TargetMachine>();
SubtargetInfo = TM->getSubtargetImpl(F);
TLI = SubtargetInfo->getTargetLowering();
TRI = SubtargetInfo->getRegisterInfo();
TLInfo = &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
TTI = &getAnalysis<TargetTransformInfoWrapperPass>().getTTI(F);
LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
BPI.reset(new BranchProbabilityInfo(F, *LI));
BFI.reset(new BlockFrequencyInfo(F, *BPI, *LI));
OptSize = F.optForSize();
ProfileSummaryInfo *PSI =
if (ProfileGuidedSectionPrefix) {
if (PSI->isFunctionHotInCallGraph(&F, *BFI))
else if (PSI->isFunctionColdInCallGraph(&F, *BFI))
/// This optimization identifies DIV instructions that can be
/// profitably bypassed and carried out with a shorter, faster divide.
if (!OptSize && !PSI->hasHugeWorkingSetSize() && TLI &&
TLI->isSlowDivBypassed()) {
const DenseMap<unsigned int, unsigned int> &BypassWidths =
BasicBlock* BB = &*F.begin();
while (BB != nullptr) {
// bypassSlowDivision may create new BBs, but we don't want to reapply the
// optimization to those blocks.
BasicBlock* Next = BB->getNextNode();
EverMadeChange |= bypassSlowDivision(BB, BypassWidths);
BB = Next;
// Eliminate blocks that contain only PHI nodes and an
// unconditional branch.
EverMadeChange |= eliminateMostlyEmptyBlocks(F);
// llvm.dbg.value is far away from the value then iSel may not be able
// handle it properly. iSel will drop llvm.dbg.value if it can not
// find a node corresponding to the value.
EverMadeChange |= placeDbgValues(F);
if (!DisableBranchOpts)
EverMadeChange |= splitBranchCondition(F);
// Split some critical edges where one of the sources is an indirect branch,
// to help generate sane code for PHIs involving such edges.
EverMadeChange |= SplitIndirectBrCriticalEdges(F);
bool MadeChange = true;
while (MadeChange) {
MadeChange = false;
for (Function::iterator I = F.begin(); I != F.end(); ) {
BasicBlock *BB = &*I++;
bool ModifiedDTOnIteration = false;
MadeChange |= optimizeBlock(*BB, ModifiedDTOnIteration);
// Restart BB iteration if the dominator tree of the Function was changed
if (ModifiedDTOnIteration)
if (EnableTypePromotionMerge && !ValToSExtendedUses.empty())
MadeChange |= mergeSExts(F);
if (!LargeOffsetGEPMap.empty())
MadeChange |= splitLargeGEPOffsets();
// Really free removed instructions during promotion.
for (Instruction *I : RemovedInsts)
EverMadeChange |= MadeChange;
if (!DisableBranchOpts) {
MadeChange = false;
// Use a set vector to get deterministic iteration order. The order the
// blocks are removed may affect whether or not PHI nodes in successors
// are removed.
SmallSetVector<BasicBlock*, 8> WorkList;
for (BasicBlock &BB : F) {
SmallVector<BasicBlock *, 2> Successors(succ_begin(&BB), succ_end(&BB));
MadeChange |= ConstantFoldTerminator(&BB, true);
if (!MadeChange) continue;
for (SmallVectorImpl<BasicBlock*>::iterator
II = Successors.begin(), IE = Successors.end(); II != IE; ++II)
if (pred_begin(*II) == pred_end(*II))
// Delete the dead blocks and any of their dead successors.
MadeChange |= !WorkList.empty();
while (!WorkList.empty()) {
BasicBlock *BB = WorkList.pop_back_val();
SmallVector<BasicBlock*, 2> Successors(succ_begin(BB), succ_end(BB));
for (SmallVectorImpl<BasicBlock*>::iterator
II = Successors.begin(), IE = Successors.end(); II != IE; ++II)
if (pred_begin(*II) == pred_end(*II))
// Merge pairs of basic blocks with unconditional branches, connected by
// a single edge.
if (EverMadeChange || MadeChange)
MadeChange |= eliminateFallThrough(F);
EverMadeChange |= MadeChange;
if (!DisableGCOpts) {
SmallVector<Instruction *, 2> Statepoints;
for (BasicBlock &BB : F)
for (Instruction &I : BB)
if (isStatepoint(I))
for (auto &I : Statepoints)
EverMadeChange |= simplifyOffsetableRelocate(*I);
return EverMadeChange;
/// Merge basic blocks which are connected by a single edge, where one of the
/// basic blocks has a single successor pointing to the other basic block,
/// which has a single predecessor.
bool CodeGenPrepare::eliminateFallThrough(Function &F) {
bool Changed = false;
// Scan all of the blocks in the function, except for the entry block.
// Use a temporary array to avoid iterator being invalidated when
// deleting blocks.
SmallVector<WeakTrackingVH, 16> Blocks;
for (auto &Block : llvm::make_range(std::next(F.begin()), F.end()))
for (auto &Block : Blocks) {
auto *BB = cast_or_null<BasicBlock>(Block);
if (!BB)
// If the destination block has a single pred, then this is a trivial
// edge, just collapse it.
BasicBlock *SinglePred = BB->getSinglePredecessor();
// Don't merge if BB's address is taken.
if (!SinglePred || SinglePred == BB || BB->hasAddressTaken()) continue;
BranchInst *Term = dyn_cast<BranchInst>(SinglePred->getTerminator());
if (Term && !Term->isConditional()) {
Changed = true;
LLVM_DEBUG(dbgs() << "To merge:\n" << *BB << "\n\n\n");
// Merge BB into SinglePred and delete it.
return Changed;
/// Find a destination block from BB if BB is mergeable empty block.
BasicBlock *CodeGenPrepare::findDestBlockOfMergeableEmptyBlock(BasicBlock *BB) {
// If this block doesn't end with an uncond branch, ignore it.
BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator());
if (!BI || !BI->isUnconditional())
return nullptr;
// If the instruction before the branch (skipping debug info) isn't a phi
// node, then other stuff is happening here.
BasicBlock::iterator BBI = BI->getIterator();
if (BBI != BB->begin()) {
while (isa<DbgInfoIntrinsic>(BBI)) {
if (BBI == BB->begin())
if (!isa<DbgInfoIntrinsic>(BBI) && !isa<PHINode>(BBI))
return nullptr;
// Do not break infinite loops.
BasicBlock *DestBB = BI->getSuccessor(0);
if (DestBB == BB)
return nullptr;
if (!canMergeBlocks(BB, DestBB))
DestBB = nullptr;
return DestBB;
/// Eliminate blocks that contain only PHI nodes, debug info directives, and an
/// unconditional branch. Passes before isel (e.g. LSR/loopsimplify) often split
/// edges in ways that are non-optimal for isel. Start by eliminating these
/// blocks so we can split them the way we want them.
bool CodeGenPrepare::eliminateMostlyEmptyBlocks(Function &F) {
SmallPtrSet<BasicBlock *, 16> Preheaders;
SmallVector<Loop *, 16> LoopList(LI->begin(), LI->end());
while (!LoopList.empty()) {
Loop *L = LoopList.pop_back_val();
LoopList.insert(LoopList.end(), L->begin(), L->end());
if (BasicBlock *Preheader = L->getLoopPreheader())
bool MadeChange = false;
// Copy blocks into a temporary array to avoid iterator invalidation issues
// as we remove them.
// Note that this intentionally skips the entry block.
SmallVector<WeakTrackingVH, 16> Blocks;
for (auto &Block : llvm::make_range(std::next(F.begin()), F.end()))
for (auto &Block : Blocks) {
BasicBlock *BB = cast_or_null<BasicBlock>(Block);
if (!BB)
BasicBlock *DestBB = findDestBlockOfMergeableEmptyBlock(BB);
if (!DestBB ||
!isMergingEmptyBlockProfitable(BB, DestBB, Preheaders.count(BB)))
MadeChange = true;
return MadeChange;
bool CodeGenPrepare::isMergingEmptyBlockProfitable(BasicBlock *BB,
BasicBlock *DestBB,
bool isPreheader) {
// Do not delete loop preheaders if doing so would create a critical edge.
// Loop preheaders can be good locations to spill registers. If the
// preheader is deleted and we create a critical edge, registers may be
// spilled in the loop body instead.
if (!DisablePreheaderProtect && isPreheader &&
!(BB->getSinglePredecessor() &&
return false;
// Try to skip merging if the unique predecessor of BB is terminated by a
// switch or indirect branch instruction, and BB is used as an incoming block
// of PHIs in DestBB. In such case, merging BB and DestBB would cause ISel to
// add COPY instructions in the predecessor of BB instead of BB (if it is not
// merged). Note that the critical edge created by merging such blocks wont be
// split in MachineSink because the jump table is not analyzable. By keeping
// such empty block (BB), ISel will place COPY instructions in BB, not in the
// predecessor of BB.
BasicBlock *Pred = BB->getUniquePredecessor();
if (!Pred ||
!(isa<SwitchInst>(Pred->getTerminator()) ||
return true;
if (BB->getTerminator() != BB->getFirstNonPHI())
return true;
// We use a simple cost heuristic which determine skipping merging is
// profitable if the cost of skipping merging is less than the cost of
// merging : Cost(skipping merging) < Cost(merging BB), where the
// Cost(skipping merging) is Freq(BB) * (Cost(Copy) + Cost(Branch)), and
// the Cost(merging BB) is Freq(Pred) * Cost(Copy).
// Assuming Cost(Copy) == Cost(Branch), we could simplify it to :
// Freq(Pred) / Freq(BB) > 2.
// Note that if there are multiple empty blocks sharing the same incoming
// value for the PHIs in the DestBB, we consider them together. In such
// case, Cost(merging BB) will be the sum of their frequencies.
if (!isa<PHINode>(DestBB->begin()))
return true;
SmallPtrSet<BasicBlock *, 16> SameIncomingValueBBs;
// Find all other incoming blocks from which incoming values of all PHIs in
// DestBB are the same as the ones from BB.
for (pred_iterator PI = pred_begin(DestBB), E = pred_end(DestBB); PI != E;
++PI) {
BasicBlock *DestBBPred = *PI;
if (DestBBPred == BB)
if (llvm::all_of(DestBB->phis(), [&](const PHINode &DestPN) {
return DestPN.getIncomingValueForBlock(BB) ==
// See if all BB's incoming values are same as the value from Pred. In this
// case, no reason to skip merging because COPYs are expected to be place in
// Pred already.
if (SameIncomingValueBBs.count(Pred))
return true;
BlockFrequency PredFreq = BFI->getBlockFreq(Pred);
BlockFrequency BBFreq = BFI->getBlockFreq(BB);
for (auto SameValueBB : SameIncomingValueBBs)
if (SameValueBB->getUniquePredecessor() == Pred &&
DestBB == findDestBlockOfMergeableEmptyBlock(SameValueBB))
BBFreq += BFI->getBlockFreq(SameValueBB);
return PredFreq.getFrequency() <=
BBFreq.getFrequency() * FreqRatioToSkipMerge;
/// Return true if we can merge BB into DestBB if there is a single
/// unconditional branch between them, and BB contains no other non-phi
/// instructions.
bool CodeGenPrepare::canMergeBlocks(const BasicBlock *BB,
const BasicBlock *DestBB) const {
// We only want to eliminate blocks whose phi nodes are used by phi nodes in
// the successor. If there are more complex condition (e.g. preheaders),
// don't mess around with them.
for (const PHINode &PN : BB->phis()) {
for (const User *U : PN.users()) {
const Instruction *UI = cast<Instruction>(U);
if (UI->getParent() != DestBB || !isa<PHINode>(UI))
return false;
// If User is inside DestBB block and it is a PHINode then check
// incoming value. If incoming value is not from BB then this is
// a complex condition (e.g. preheaders) we want to avoid here.
if (UI->getParent() == DestBB) {
if (const PHINode *UPN = dyn_cast<PHINode>(UI))
for (unsigned I = 0, E = UPN->getNumIncomingValues(); I != E; ++I) {
Instruction *Insn = dyn_cast<Instruction>(UPN->getIncomingValue(I));
if (Insn && Insn->getParent() == BB &&
Insn->getParent() != UPN->getIncomingBlock(I))
return false;
// If BB and DestBB contain any common predecessors, then the phi nodes in BB
// and DestBB may have conflicting incoming values for the block. If so, we
// can't merge the block.
const PHINode *DestBBPN = dyn_cast<PHINode>(DestBB->begin());
if (!DestBBPN) return true; // no conflict.
// Collect the preds of BB.
SmallPtrSet<const BasicBlock*, 16> BBPreds;
if (const PHINode *BBPN = dyn_cast<PHINode>(BB->begin())) {
// It is faster to get preds from a PHI than with pred_iterator.
for (unsigned i = 0, e = BBPN->getNumIncomingValues(); i != e; ++i)
} else {
BBPreds.insert(pred_begin(BB), pred_end(BB));
// Walk the preds of DestBB.
for (unsigned i = 0, e = DestBBPN->getNumIncomingValues(); i != e; ++i) {
BasicBlock *Pred = DestBBPN->getIncomingBlock(i);
if (BBPreds.count(Pred)) { // Common predecessor?
for (const PHINode &PN : DestBB->phis()) {
const Value *V1 = PN.getIncomingValueForBlock(Pred);
const Value *V2 = PN.getIncomingValueForBlock(BB);
// If V2 is a phi node in BB, look up what the mapped value will be.
if (const PHINode *V2PN = dyn_cast<PHINode>(V2))
if (V2PN->getParent() == BB)
V2 = V2PN->getIncomingValueForBlock(Pred);
// If there is a conflict, bail out.
if (V1 != V2) return false;
return true;
/// Eliminate a basic block that has only phi's and an unconditional branch in
/// it.
void CodeGenPrepare::eliminateMostlyEmptyBlock(BasicBlock *BB) {
BranchInst *BI = cast<BranchInst>(BB->getTerminator());
BasicBlock *DestBB = BI->getSuccessor(0);
<< *BB << *DestBB);
// If the destination block has a single pred, then this is a trivial edge,
// just collapse it.
if (BasicBlock *SinglePred = DestBB->getSinglePredecessor()) {
if (SinglePred != DestBB) {
assert(SinglePred == BB &&
"Single predecessor not the same as predecessor");
// Merge DestBB into SinglePred/BB and delete it.
// Note: BB(=SinglePred) will not be deleted on this path.
// DestBB(=its single successor) is the one that was deleted.
LLVM_DEBUG(dbgs() << "AFTER:\n" << *SinglePred << "\n\n\n");
// Otherwise, we have multiple predecessors of BB. Update the PHIs in DestBB
// to handle the new incoming edges it is about to have.
for (PHINode &PN : DestBB->phis()) {
// Remove the incoming value for BB, and remember it.
Value *InVal = PN.removeIncomingValue(BB, false);
// Two options: either the InVal is a phi node defined in BB or it is some
// value that dominates BB.
PHINode *InValPhi = dyn_cast<PHINode>(InVal);
if (InValPhi && InValPhi->getParent() == BB) {
// Add all of the input values of the input PHI as inputs of this phi.
for (unsigned i = 0, e = InValPhi->getNumIncomingValues(); i != e; ++i)
} else {
// Otherwise, add one instance of the dominating value for each edge that
// we will be adding.
if (PHINode *BBPN = dyn_cast<PHINode>(BB->begin())) {
for (unsigned i = 0, e = BBPN->getNumIncomingValues(); i != e; ++i)
PN.addIncoming(InVal, BBPN->getIncomingBlock(i));
} else {
for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
PN.addIncoming(InVal, *PI);
// The PHIs are now updated, change everything that refers to BB to use
// DestBB and remove BB.
LLVM_DEBUG(dbgs() << "AFTER:\n" << *DestBB << "\n\n\n");
// Computes a map of base pointer relocation instructions to corresponding
// derived pointer relocation instructions given a vector of all relocate calls
static void computeBaseDerivedRelocateMap(
const SmallVectorImpl<GCRelocateInst *> &AllRelocateCalls,
DenseMap<GCRelocateInst *, SmallVector<GCRelocateInst *, 2>>
&RelocateInstMap) {
// Collect information in two maps: one primarily for locating the base object
// while filling the second map; the second map is the final structure holding
// a mapping between Base and corresponding Derived relocate calls
DenseMap<std::pair<unsigned, unsigned>, GCRelocateInst *> RelocateIdxMap;
for (auto *ThisRelocate : AllRelocateCalls) {
auto K = std::make_pair(ThisRelocate->getBasePtrIndex(),
RelocateIdxMap.insert(std::make_pair(K, ThisRelocate));
for (auto &Item : RelocateIdxMap) {
std::pair<unsigned, unsigned> Key = Item.first;
if (Key.first == Key.second)
// Base relocation: nothing to insert
GCRelocateInst *I = Item.second;
auto BaseKey = std::make_pair(Key.first, Key.first);
// We're iterating over RelocateIdxMap so we cannot modify it.
auto MaybeBase = RelocateIdxMap.find(BaseKey);
if (MaybeBase == RelocateIdxMap.end())
// TODO: We might want to insert a new base object relocate and gep off
// that, if there are enough derived object relocates.
// Accepts a GEP and extracts the operands into a vector provided they're all
// small integer constants
static bool getGEPSmallConstantIntOffsetV(GetElementPtrInst *GEP,
SmallVectorImpl<Value *> &OffsetV) {
for (unsigned i = 1; i < GEP->getNumOperands(); i++) {
// Only accept small constant integer operands
auto Op = dyn_cast<ConstantInt>(GEP->getOperand(i));
if (!Op || Op->getZExtValue() > 20)
return false;
for (unsigned i = 1; i < GEP->getNumOperands(); i++)
return true;
// Takes a RelocatedBase (base pointer relocation instruction) and Targets to
// replace, computes a replacement, and affects it.
static bool
simplifyRelocatesOffABase(GCRelocateInst *RelocatedBase,
const SmallVectorImpl<GCRelocateInst *> &Targets) {
bool MadeChange = false;
// We must ensure the relocation of derived pointer is defined after
// relocation of base pointer. If we find a relocation corresponding to base
// defined earlier than relocation of base then we move relocation of base
// right before found relocation. We consider only relocation in the same
// basic block as relocation of base. Relocations from other basic block will
// be skipped by optimization and we do not care about them.
for (auto R = RelocatedBase->getParent()->getFirstInsertionPt();
&*R != RelocatedBase; ++R)
if (auto RI = dyn_cast<GCRelocateInst>(R))
if (RI->getStatepoint() == RelocatedBase->getStatepoint())
if (RI->getBasePtrIndex() == RelocatedBase->getBasePtrIndex()) {
for (GCRelocateInst *ToReplace : Targets) {
assert(ToReplace->getBasePtrIndex() == RelocatedBase->getBasePtrIndex() &&
"Not relocating a derived object of the original base object");
if (ToReplace->getBasePtrIndex() == ToReplace->getDerivedPtrIndex()) {
// A duplicate relocate call. TODO: coalesce duplicates.
if (RelocatedBase->getParent() != ToReplace->getParent()) {
// Base and derived relocates are in different basic blocks.
// In this case transform is only valid when base dominates derived
// relocate. However it would be too expensive to check dominance
// for each such relocate, so we skip the whole transformation.
Value *Base = ToReplace->getBasePtr();
auto Derived = dyn_cast<GetElementPtrInst>(ToReplace->getDerivedPtr());
if (!Derived || Derived->getPointerOperand() != Base)
SmallVector<Value *, 2> OffsetV;
if (!getGEPSmallConstantIntOffsetV(Derived, OffsetV))
// Create a Builder and replace the target callsite with a gep
assert(RelocatedBase->getNextNode() &&
"Should always have one since it's not a terminator");
// Insert after RelocatedBase
IRBuilder<> Builder(RelocatedBase->getNextNode());
// If gc_relocate does not match the actual type, cast it to the right type.
// In theory, there must be a bitcast after gc_relocate if the type does not
// match, and we should reuse it to get the derived pointer. But it could be
// cases like this:
// bb1:
// ...
// %g1 = call coldcc i8 addrspace(1)* @llvm.experimental.gc.relocate.p1i8(...)
// br label %merge
// bb2:
// ...
// %g2 = call coldcc i8 addrspace(1)* @llvm.experimental.gc.relocate.p1i8(...)
// br label %merge
// merge:
// %p1 = phi i8 addrspace(1)* [ %g1, %bb1 ], [ %g2, %bb2 ]
// %cast = bitcast i8 addrspace(1)* %p1 in to i32 addrspace(1)*
// In this case, we can not find the bitcast any more. So we insert a new bitcast
// no matter there is already one or not. In this way, we can handle all cases, and
// the extra bitcast should be optimized away in later passes.
Value *ActualRelocatedBase = RelocatedBase;
if (RelocatedBase->getType() != Base->getType()) {
ActualRelocatedBase =
Builder.CreateBitCast(RelocatedBase, Base->getType());
Value *Replacement = Builder.CreateGEP(
Derived->getSourceElementType(), ActualRelocatedBase, makeArrayRef(OffsetV));
// If the newly generated derived pointer's type does not match the original derived
// pointer's type, cast the new derived pointer to match it. Same reasoning as above.
Value *ActualReplacement = Replacement;
if (Replacement->getType() != ToReplace->getType()) {
ActualReplacement =
Builder.CreateBitCast(Replacement, ToReplace->getType());
MadeChange = true;
return MadeChange;
// Turns this:
// %base = ...
// %ptr = gep %base + 15
// %tok = statepoint (%fun, i32 0, i32 0, i32 0, %base, %ptr)
// %base' = relocate(%tok, i32 4, i32 4)
// %ptr' = relocate(%tok, i32 4, i32 5)
// %val = load %ptr'
// into this:
// %base = ...
// %ptr = gep %base + 15
// %tok = statepoint (%fun, i32 0, i32 0, i32 0, %base, %ptr)
// %base' = gc.relocate(%tok, i32 4, i32 4)
// %ptr' = gep %base' + 15
// %val = load %ptr'
bool CodeGenPrepare::simplifyOffsetableRelocate(Instruction &I) {
bool MadeChange = false;
SmallVector<GCRelocateInst *, 2> AllRelocateCalls;
for (auto *U : I.users())
if (GCRelocateInst *Relocate = dyn_cast<GCRelocateInst>(U))
// Collect all the relocate calls associated with a statepoint
// We need atleast one base pointer relocation + one derived pointer
// relocation to mangle
if (AllRelocateCalls.size() < 2)
return false;
// RelocateInstMap is a mapping from the base relocate instruction to the
// corresponding derived relocate instructions
DenseMap<GCRelocateInst *, SmallVector<GCRelocateInst *, 2>> RelocateInstMap;
computeBaseDerivedRelocateMap(AllRelocateCalls, RelocateInstMap);
if (RelocateInstMap.empty())
return false;
for (auto &Item : RelocateInstMap)
// Item.first is the RelocatedBase to offset against
// Item.second is the vector of Targets to replace
MadeChange = simplifyRelocatesOffABase(Item.first, Item.second);
return MadeChange;
/// SinkCast - Sink the specified cast instruction into its user blocks
static bool SinkCast(CastInst *CI) {
BasicBlock *DefBB = CI->getParent();
/// InsertedCasts - Only insert a cast in each block once.
DenseMap<BasicBlock*, CastInst*> InsertedCasts;
bool MadeChange = false;
for (Value::user_iterator UI = CI->user_begin(), E = CI->user_end();
UI != E; ) {
Use &TheUse = UI.getUse();
Instruction *User = cast<Instruction>(*UI);
// Figure out which BB this cast is used in. For PHI's this is the
// appropriate predecessor block.
BasicBlock *UserBB = User->getParent();
if (PHINode *PN = dyn_cast<PHINode>(User)) {
UserBB = PN->getIncomingBlock(TheUse);
// Preincrement use iterator so we don't invalidate it.
// The first insertion point of a block containing an EH pad is after the
// pad. If the pad is the user, we cannot sink the cast past the pad.
if (User->isEHPad())
// If the block selected to receive the cast is an EH pad that does not
// allow non-PHI instructions before the terminator, we can't sink the
// cast.
if (UserBB->getTerminator()->isEHPad())
// If this user is in the same block as the cast, don't change the cast.
if (UserBB == DefBB) continue;
// If we have already inserted a cast into this block, use it.
CastInst *&InsertedCast = InsertedCasts[UserBB];
if (!InsertedCast) {
BasicBlock::iterator InsertPt = UserBB->getFirstInsertionPt();
assert(InsertPt != UserBB->end());
InsertedCast = CastInst::Create(CI->getOpcode(), CI->getOperand(0),
CI->getType(), "", &*InsertPt);
// Replace a use of the cast with a use of the new cast.
TheUse = InsertedCast;
MadeChange = true;
// If we removed all uses, nuke the cast.
if (CI->use_empty()) {
MadeChange = true;
return MadeChange;
/// If the specified cast instruction is a noop copy (e.g. it's casting from
/// one pointer type to another, i32->i8 on PPC), sink it into user blocks to
/// reduce the number of virtual registers that must be created and coalesced.
/// Return true if any changes are made.
static bool OptimizeNoopCopyExpression(CastInst *CI, const TargetLowering &TLI,
const DataLayout &DL) {
// Sink only "cheap" (or nop) address-space casts. This is a weaker condition
// than sinking only nop casts, but is helpful on some platforms.
if (auto *ASC = dyn_cast<AddrSpaceCastInst>(CI)) {
if (!TLI.isCheapAddrSpaceCast(ASC->getSrcAddressSpace(),
return false;
// If this is a noop copy,
EVT SrcVT = TLI.getValueType(DL, CI->getOperand(0)->getType());
EVT DstVT = TLI.getValueType(DL, CI->getType());
// This is an fp<->int conversion?
if (SrcVT.isInteger() != DstVT.isInteger())
return false;
// If this is an extension, it will be a zero or sign extension, which
// isn't a noop.
if (SrcVT.bitsLT(DstVT)) return false;
// If these values will be promoted, find out what they will be promoted
// to. This helps us consider truncates on PPC as noop copies when they
// are.
if (TLI.getTypeAction(CI->getContext(), SrcVT) ==
SrcVT = TLI.getTypeToTransformTo(CI->getContext(), SrcVT);
if (TLI.getTypeAction(CI->getContext(), DstVT) ==
DstVT = TLI.getTypeToTransformTo(CI->getContext(), DstVT);
// If, after promotion, these are the same types, this is a noop copy.
if (SrcVT != DstVT)
return false;
return SinkCast(CI);
/// Try to combine CI into a call to the llvm.uadd.with.overflow intrinsic if
/// possible.
/// Return true if any changes were made.
static bool CombineUAddWithOverflow(CmpInst *CI) {
Value *A, *B;
Instruction *AddI;
if (!match(CI,
m_UAddWithOverflow(m_Value(A), m_Value(B), m_Instruction(AddI))))
return false;
Type *Ty = AddI->getType();
if (!isa<IntegerType>(Ty))
return false;
// We don't want to move around uses of condition values this late, so we we
// check if it is legal to create the call to the intrinsic in the basic
// block containing the icmp:
if (AddI->getParent() != CI->getParent() && !AddI->hasOneUse())
return false;
#ifndef NDEBUG
// Someday m_UAddWithOverflow may get smarter, but this is a safe assumption
// for now:
if (AddI->hasOneUse())
assert(*AddI->user_begin() == CI && "expected!");
Module *M = CI->getModule();
Value *F = Intrinsic::getDeclaration(M, Intrinsic::uadd_with_overflow, Ty);
auto *InsertPt = AddI->hasOneUse() ? CI : AddI;
auto *UAddWithOverflow =
CallInst::Create(F, {A, B}, "uadd.overflow", InsertPt);
auto *UAdd = ExtractValueInst::Create(UAddWithOverflow, 0, "uadd", InsertPt);
auto *Overflow =
ExtractValueInst::Create(UAddWithOverflow, 1, "overflow", InsertPt);
return true;
/// Sink the given CmpInst into user blocks to reduce the number of virtual
/// registers that must be created and coalesced. This is a clear win except on
/// targets with multiple condition code registers (PowerPC), where it might
/// lose; some adjustment may be wanted there.
/// Return true if any changes are made.
static bool SinkCmpExpression(CmpInst *CI, const TargetLowering *TLI) {
BasicBlock *DefBB = CI->getParent();
// Avoid sinking soft-FP comparisons, since this can move them into a loop.
if (TLI && TLI->useSoftFloat() && isa<FCmpInst>(CI))
return false;
// Only insert a cmp in each block once.
DenseMap<BasicBlock*, CmpInst*> InsertedCmps;
bool MadeChange = false;
for (Value::user_iterator UI = CI->user_begin(), E = CI->user_end();
UI != E; ) {
Use &TheUse = UI.getUse();
Instruction *User = cast<Instruction>(*UI);
// Preincrement use iterator so we don't invalidate it.
// Don't bother for PHI nodes.
if (isa<PHINode>(User))
// Figure out which BB this cmp is used in.
BasicBlock *UserBB = User->getParent();
// If this user is in the same block as the cmp, don't change the cmp.
if (UserBB == DefBB) continue;
// If we have already inserted a cmp into this block, use it.
CmpInst *&InsertedCmp = InsertedCmps[UserBB];
if (!InsertedCmp) {
BasicBlock::iterator InsertPt = UserBB->getFirstInsertionPt();
assert(InsertPt != UserBB->end());
InsertedCmp =
CmpInst::Create(CI->getOpcode(), CI->getPredicate(),
CI->getOperand(0), CI->getOperand(1), "", &*InsertPt);
// Propagate the debug info.
// Replace a use of the cmp with a use of the new cmp.
TheUse = InsertedCmp;
MadeChange = true;
// If we removed all uses, nuke the cmp.
if (CI->use_empty()) {
MadeChange = true;
return MadeChange;
static bool OptimizeCmpExpression(CmpInst *CI, const TargetLowering *TLI) {
if (SinkCmpExpression(CI, TLI))
return true;
if (CombineUAddWithOverflow(CI))
return true;
return false;
/// Duplicate and sink the given 'and' instruction into user blocks where it is
/// used in a compare to allow isel to generate better code for targets where
/// this operation can be combined.
/// Return true if any changes are made.
static bool sinkAndCmp0Expression(Instruction *AndI,
const TargetLowering &TLI,
SetOfInstrs &InsertedInsts) {
// Double-check that we're not trying to optimize an instruction that was
// already optimized by some other part of this pass.
assert(!InsertedInsts.count(AndI) &&
"Attempting to optimize already optimized and instruction");
(void) InsertedInsts;
// Nothing to do for single use in same basic block.
if (AndI->hasOneUse() &&
AndI->getParent() == cast<Instruction>(*AndI->user_begin())->getParent())
return false;
// Try to avoid cases where sinking/duplicating is likely to increase register
// pressure.
if (!isa<ConstantInt>(AndI->getOperand(0)) &&
!isa<ConstantInt>(AndI->getOperand(1)) &&
AndI->getOperand(0)->hasOneUse() && AndI->getOperand(1)->hasOneUse())
return false;
for (auto *U : AndI->users()) {
Instruction *User = cast<Instruction>(U);
// Only sink for and mask feeding icmp with 0.
if (!isa<ICmpInst>(User))
return false;
auto *CmpC = dyn_cast<ConstantInt>(User->getOperand(1));
if (!CmpC || !CmpC->isZero())
return false;
if (!TLI.isMaskAndCmp0FoldingBeneficial(*AndI))
return false;
LLVM_DEBUG(dbgs() << "found 'and' feeding only icmp 0;\n");
// Push the 'and' into the same block as the icmp 0. There should only be
// one (icmp (and, 0)) in each block, since CSE/GVN should have removed any
// others, so we don't need to keep track of which BBs we insert into.
for (Value::user_iterator UI = AndI->user_begin(), E = AndI->user_end();
UI != E; ) {
Use &TheUse = UI.getUse();
Instruction *User = cast<Instruction>(*UI);
// Preincrement use iterator so we don't invalidate it.
LLVM_DEBUG(dbgs() << "sinking 'and' use: " << *User << "\n");
// Keep the 'and' in the same place if the use is already in the same block.
Instruction *InsertPt =
User->getParent() == AndI->getParent() ? AndI : User;
Instruction *InsertedAnd =
BinaryOperator::Create(Instruction::And, AndI->getOperand(0),
AndI->getOperand(1), "", InsertPt);
// Propagate the debug info.
// Replace a use of the 'and' with a use of the new 'and'.
TheUse = InsertedAnd;
// We removed all uses, nuke the and.
return true;
/// Check if the candidates could be combined with a shift instruction, which
/// includes:
/// 1. Truncate instruction
/// 2. And instruction and the imm is a mask of the low bits:
/// imm & (imm+1) == 0
static bool isExtractBitsCandidateUse(Instruction *User) {
if (!isa<TruncInst>(User)) {
if (User->getOpcode() != Instruction::And ||
return false;
const APInt &Cimm = cast<ConstantInt>(User->getOperand(1))->getValue();
if ((Cimm & (Cimm + 1)).getBoolValue())
return false;
return true;
/// Sink both shift and truncate instruction to the use of truncate's BB.
static bool
SinkShiftAndTruncate(BinaryOperator *ShiftI, Instruction *User, ConstantInt *CI,
DenseMap<BasicBlock *, BinaryOperator *> &InsertedShifts,
const TargetLowering &TLI, const DataLayout &DL) {
BasicBlock *UserBB = User->getParent();
DenseMap<BasicBlock *, CastInst *> InsertedTruncs;
TruncInst *TruncI = dyn_cast<TruncInst>(User);
bool MadeChange = false;
for (Value::user_iterator TruncUI = TruncI->user_begin(),
TruncE = TruncI->user_end();
TruncUI != TruncE;) {
Use &TruncTheUse = TruncUI.getUse();
Instruction *TruncUser = cast<Instruction>(*TruncUI);
// Preincrement use iterator so we don't invalidate it.
int ISDOpcode = TLI.InstructionOpcodeToISD(TruncUser->getOpcode());
if (!ISDOpcode)
// If the use is actually a legal node, there will not be an
// implicit truncate.
// FIXME: always querying the result type is just an
// approximation; some nodes' legality is determined by the
// operand or other means. There's no good way to find out though.
if (TLI.isOperationLegalOrCustom(
ISDOpcode, TLI.getValueType(DL, TruncUser->getType(), true)))
// Don't bother for PHI nodes.
if (isa<PHINode>(TruncUser))
BasicBlock *TruncUserBB = TruncUser->getParent();
if (UserBB == TruncUserBB)
BinaryOperator *&InsertedShift = InsertedShifts[TruncUserBB];
CastInst *&InsertedTrunc = InsertedTruncs[TruncUserBB];
if (!InsertedShift && !InsertedTrunc) {
BasicBlock::iterator InsertPt = TruncUserBB->getFirstInsertionPt();
assert(InsertPt != TruncUserBB->end());
// Sink the shift
if (ShiftI->getOpcode() == Instruction::AShr)
InsertedShift = BinaryOperator::CreateAShr(ShiftI->getOperand(0), CI,
"", &*InsertPt);
InsertedShift = BinaryOperator::CreateLShr(ShiftI->getOperand(0), CI,
"", &*InsertPt);
// Sink the trunc
BasicBlock::iterator TruncInsertPt = TruncUserBB->getFirstInsertionPt();
assert(TruncInsertPt != TruncUserBB->end());
InsertedTrunc = CastInst::Create(TruncI->getOpcode(), InsertedShift,
TruncI->getType(), "", &*TruncInsertPt);
MadeChange = true;
TruncTheUse = InsertedTrunc;
return MadeChange;
/// Sink the shift *right* instruction into user blocks if the uses could
/// potentially be combined with this shift instruction and generate BitExtract
/// instruction. It will only be applied if the architecture supports BitExtract
/// instruction. Here is an example:
/// BB1:
/// %x.extract.shift = lshr i64 %arg1, 32
/// BB2:
/// %x.extract.trunc = trunc i64 %x.extract.shift to i16
/// ==>
/// BB2:
/// %x.extract.shift.1 = lshr i64 %arg1, 32
/// %x.extract.trunc = trunc i64 %x.extract.shift.1 to i16
/// CodeGen will recognize the pattern in BB2 and generate BitExtract
/// instruction.
/// Return true if any changes are made.
static bool OptimizeExtractBits(BinaryOperator *ShiftI, ConstantInt *CI,
const TargetLowering &TLI,
const DataLayout &DL) {
BasicBlock *DefBB = ShiftI->getParent();
/// Only insert instructions in each block once.
DenseMap<BasicBlock *, BinaryOperator *> InsertedShifts;
bool shiftIsLegal = TLI.isTypeLegal(TLI.getValueType(DL, ShiftI->getType()));
bool MadeChange = false;
for (Value::user_iterator UI = ShiftI->user_begin(), E = ShiftI->user_end();
UI != E;) {
Use &TheUse = UI.getUse();
Instruction *User = cast<Instruction>(*UI);
// Preincrement use iterator so we don't invalidate it.
// Don't bother for PHI nodes.
if (isa<PHINode>(User))
if (!isExtractBitsCandidateUse(User))
BasicBlock *UserBB = User->getParent();
if (UserBB == DefBB) {
// If the shift and truncate instruction are in the same BB. The use of
// the truncate(TruncUse) may still introduce another truncate if not
// legal. In this case, we would like to sink both shift and truncate
// instruction to the BB of TruncUse.
// for example:
// BB1:
// i64 shift.result = lshr i64 opnd, imm
// trunc.result = trunc shift.result to i16
// BB2:
// ----> We will have an implicit truncate here if the architecture does
// not have i16 compare.
// cmp i16 trunc.result, opnd2
if (isa<TruncInst>(User) && shiftIsLegal
// If the type of the truncate is legal, no truncate will be
// introduced in other basic blocks.
(!TLI.isTypeLegal(TLI.getValueType(DL, User->getType()))))
MadeChange =
SinkShiftAndTruncate(ShiftI, User, CI, InsertedShifts, TLI, DL);
// If we have already inserted a shift into this block, use it.
BinaryOperator *&InsertedShift = InsertedShifts[UserBB];
if (!InsertedShift) {
BasicBlock::iterator InsertPt = UserBB->getFirstInsertionPt();
assert(InsertPt != UserBB->end());
if (ShiftI->getOpcode() == Instruction::AShr)
InsertedShift = BinaryOperator::CreateAShr(ShiftI->getOperand(0), CI,
"", &*InsertPt);
InsertedShift = BinaryOperator::CreateLShr(ShiftI->getOperand(0), CI,
"", &*InsertPt);
MadeChange = true;
// Replace a use of the shift with a use of the new shift.
TheUse = InsertedShift;
// If we removed all uses, nuke the shift.
if (ShiftI->use_empty())
return MadeChange;
/// If counting leading or trailing zeros is an expensive operation and a zero
/// input is defined, add a check for zero to avoid calling the intrinsic.
/// We want to transform:
/// %z = call i64 @llvm.cttz.i64(i64 %A, i1 false)
/// into:
/// entry:
/// %cmpz = icmp eq i64 %A, 0
/// br i1 %cmpz, label %cond.end, label %cond.false
/// cond.false:
/// %z = call i64 @llvm.cttz.i64(i64 %A, i1 true)
/// br label %cond.end
/// cond.end:
/// %ctz = phi i64 [ 64, %entry ], [ %z, %cond.false ]
/// If the transform is performed, return true and set ModifiedDT to true.
static bool despeculateCountZeros(IntrinsicInst *CountZeros,
const TargetLowering *TLI,
const DataLayout *DL,
bool &ModifiedDT) {
if (!TLI || !DL)
return false;
// If a zero input is undefined, it doesn't make sense to despeculate that.
if (match(CountZeros->getOperand(1), m_One()))
return false;
// If it's cheap to speculate, there's nothing to do.
auto IntrinsicID = CountZeros->getIntrinsicID();
if ((IntrinsicID == Intrinsic::cttz && TLI->isCheapToSpeculateCttz()) ||
(IntrinsicID == Intrinsic::ctlz && TLI->isCheapToSpeculateCtlz()))
return false;
// Only handle legal scalar cases. Anything else requires too much work.
Type *Ty = CountZeros->getType();
unsigned SizeInBits = Ty->getPrimitiveSizeInBits();
if (Ty->isVectorTy() || SizeInBits > DL->getLargestLegalIntTypeSizeInBits())
return false;
// The intrinsic will be sunk behind a compare against zero and branch.
BasicBlock *StartBlock = CountZeros->getParent();
BasicBlock *CallBlock = StartBlock->splitBasicBlock(CountZeros, "cond.false");
// Create another block after the count zero intrinsic. A PHI will be added
// in this block to select the result of the intrinsic or the bit-width
// constant if the input to the intrinsic is zero.
BasicBlock::iterator SplitPt = ++(BasicBlock::iterator(CountZeros));
BasicBlock *EndBlock = CallBlock->splitBasicBlock(SplitPt, "cond.end");
// Set up a builder to create a compare, conditional branch, and PHI.
IRBuilder<> Builder(CountZeros->getContext());
// Replace the unconditional branch that was created by the first split with
// a compare against zero and a conditional branch.
Value *Zero = Constant::getNullValue(Ty);
Value *Cmp = Builder.CreateICmpEQ(CountZeros->getOperand(0), Zero, "cmpz");
Builder.CreateCondBr(Cmp, EndBlock, CallBlock);
// Create a PHI in the end block to select either the output of the intrinsic
// or the bit width of the operand.
PHINode *PN = Builder.CreatePHI(Ty, 2, "ctz");
Value *BitWidth = Builder.getInt(APInt(SizeInBits, SizeInBits));
PN->addIncoming(BitWidth, StartBlock);
PN->addIncoming(CountZeros, CallBlock);
// We are explicitly handling the zero case, so we can set the intrinsic's
// undefined zero argument to 'true'. This will also prevent reprocessing the
// intrinsic; we only despeculate when a zero input is defined.
CountZeros->setArgOperand(1, Builder.getTrue());
ModifiedDT = true;
return true;
bool CodeGenPrepare::optimizeCallInst(CallInst *CI, bool &ModifiedDT) {
BasicBlock *BB = CI->getParent();
// Lower inline assembly if we can.
// If we found an inline asm expession, and if the target knows how to
// lower it to normal LLVM code, do so now.
if (TLI && isa<InlineAsm>(CI->getCalledValue())) {
if (TLI->ExpandInlineAsm(CI)) {
// Avoid invalidating the iterator.
CurInstIterator = BB->begin();
// Avoid processing instructions out of order, which could cause
// reuse before a value is defined.
return true;
// Sink address computing for memory operands into the block.
if (optimizeInlineAsmInst(CI))
return true;
// Align the pointer arguments to this call if the target thinks it's a good
// idea
unsigned MinSize, PrefAlign;
if (TLI && TLI->shouldAlignPointerArgs(CI, MinSize, PrefAlign)) {
for (auto &Arg : CI->arg_operands()) {
// We want to align both objects whose address is used directly and
// objects whose address is used in casts and GEPs, though it only makes
// sense for GEPs if the offset is a multiple of the desired alignment and
// if size - offset meets the size threshold.
if (!Arg->getType()->isPointerTy())
APInt Offset(DL->getIndexSizeInBits(
Value *Val = Arg->stripAndAccumulateInBoundsConstantOffsets(*DL, Offset);
uint64_t Offset2 = Offset.getLimitedValue();
if ((Offset2 & (PrefAlign-1)) != 0)
AllocaInst *AI;
if ((AI = dyn_cast<AllocaInst>(Val)) && AI->getAlignment() < PrefAlign &&
DL->getTypeAllocSize(AI->getAllocatedType()) >= MinSize + Offset2)
// Global variables can only be aligned if they are defined in this
// object (i.e. they are uniquely initialized in this object), and
// over-aligning global variables that have an explicit section is
// forbidden.
GlobalVariable *GV;
if ((GV = dyn_cast<GlobalVariable>(Val)) && GV->canIncreaseAlignment() &&
GV->getPointerAlignment(*DL) < PrefAlign &&
DL->getTypeAllocSize(GV->getValueType()) >=
MinSize + Offset2)
// If this is a memcpy (or similar) then we may be able to improve the
// alignment
if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(CI)) {
unsigned DestAlign = getKnownAlignment(MI->getDest(), *DL);
if (DestAlign > MI->getDestAlignment())
if (MemTransferInst *MTI = dyn_cast<MemTransferInst>(MI)) {
unsigned SrcAlign = getKnownAlignment(MTI->getSource(), *DL);
if (SrcAlign > MTI->getSourceAlignment())
// If we have a cold call site, try to sink addressing computation into the
// cold block. This interacts with our handling for loads and stores to
// ensure that we can fold all uses of a potential addressing computation
// into their uses. TODO: generalize this to work over profiling data
if (!OptSize && CI->hasFnAttr(Attribute::Cold))
for (auto &Arg : CI->arg_operands()) {
if (!Arg->getType()->isPointerTy())
unsigned AS = Arg->getType()->getPointerAddressSpace();
return optimizeMemoryInst(CI, Arg, Arg->getType(), AS);
IntrinsicInst *II = dyn_cast<IntrinsicInst>(CI);
if (II) {
switch (II->getIntrinsicID()) {
default: break;
case Intrinsic::objectsize: {
// Lower all uses of llvm.objectsize.*
ConstantInt *RetVal =
lowerObjectSizeCall(II, *DL, TLInfo, /*MustSucceed=*/true);
// Substituting this can cause recursive simplifications, which can
// invalidate our iterator. Use a WeakTrackingVH to hold onto it in case
// this
// happens.
Value *CurValue = &*CurInstIterator;
WeakTrackingVH IterHandle(CurValue);
replaceAndRecursivelySimplify(CI, RetVal, TLInfo, nullptr);
// If the iterator instruction was recursively deleted, start over at the
// start of the block.
if (IterHandle != CurValue) {
CurInstIterator = BB->begin();
return true;
case Intrinsic::aarch64_stlxr:
case Intrinsic::aarch64_stxr: {
ZExtInst *ExtVal = dyn_cast<ZExtInst>(CI->getArgOperand(0));
if (!ExtVal || !ExtVal->hasOneUse() ||
ExtVal->getParent() == CI->getParent())
return false;
// Sink a zext feeding stlxr/stxr before it, so it can be folded into it.
// Mark this instruction as "inserted by CGP", so that other
// optimizations don't touch it.
return true;
case Intrinsic::launder_invariant_group:
case Intrinsic::strip_invariant_group:
return true;
case Intrinsic::cttz:
case Intrinsic::ctlz:
// If counting zeros is expensive, try to avoid it.
return despeculateCountZeros(II, TLI, DL, ModifiedDT);
if (TLI) {
SmallVector<Value*, 2> PtrOps;
Type *AccessTy;
if (TLI->getAddrModeArguments(II, PtrOps, AccessTy))
while (!PtrOps.empty()) {
Value *PtrVal = PtrOps.pop_back_val();
unsigned AS = PtrVal->getType()->getPointerAddressSpace();
if (optimizeMemoryInst(II, PtrVal, AccessTy, AS))
return true;
// From here on out we're working with named functions.
if (!CI->getCalledFunction()) return false;
// Lower all default uses of _chk calls. This is very similar
// to what InstCombineCalls does, but here we are only lowering calls
// to fortified library functions (e.g. __memcpy_chk) that have the default
// "don't know" as the objectsize. Anything else should be left alone.
FortifiedLibCallSimplifier Simplifier(TLInfo, true);
if (Value *V = Simplifier.optimizeCall(CI)) {
return true;
return false;
/// Look for opportunities to duplicate return instructions to the predecessor
/// to enable tail call optimizations. The case it is currently looking for is:
/// @code
/// bb0:
/// %tmp0 = tail call i32 @f0()
/// br label %return
/// bb1:
/// %tmp1 = tail call i32 @f1()
/// br label %return
/// bb2:
/// %tmp2 = tail call i32 @f2()
/// br label %return
/// return:
/// %retval = phi i32 [ %tmp0, %bb0 ], [ %tmp1, %bb1 ], [ %tmp2, %bb2 ]
/// ret i32 %retval
/// @endcode
/// =>
/// @code
/// bb0:
/// %tmp0 = tail call i32 @f0()
/// ret i32 %tmp0
/// bb1:
/// %tmp1 = tail call i32 @f1()
/// ret i32 %tmp1
/// bb2:
/// %tmp2 = tail call i32 @f2()
/// ret i32 %tmp2
/// @endcode
bool CodeGenPrepare::dupRetToEnableTailCallOpts(BasicBlock *BB) {
if (!TLI)
return false;
ReturnInst *RetI = dyn_cast<ReturnInst>(BB->getTerminator());
if (!RetI)
return false;
PHINode *PN = nullptr;
BitCastInst *BCI = nullptr;
Value *V = RetI->getReturnValue();
if (V) {
BCI = dyn_cast<BitCastInst>(V);
if (BCI)
V = BCI->getOperand(0);
PN = dyn_cast<PHINode>(V);
if (!PN)
return false;
if (PN && PN->getParent() != BB)
return false;
// Make sure there are no instructions between the PHI and return, or that the
// return is the first instruction in the block.
if (PN) {
BasicBlock::iterator BI = BB->begin();
do { ++BI; } while (isa<DbgInfoIntrinsic>(BI));
if (&*BI == BCI)
// Also skip over the bitcast.
if (&*BI != RetI)
return false;
} else {
BasicBlock::iterator BI = BB->begin();
while (isa<DbgInfoIntrinsic>(BI)) ++BI;
if (&*BI != RetI)
return false;
/// Only dup the ReturnInst if the CallInst is likely to be emitted as a tail
/// call.
const Function *F = BB->getParent();
SmallVector<CallInst*, 4> TailCalls;
if (PN) {
for (unsigned I = 0, E = PN->getNumIncomingValues(); I != E; ++I) {
CallInst *CI = dyn_cast<CallInst>(PN->getIncomingValue(I));
// Make sure the phi value is indeed produced by the tail call.
if (CI && CI->hasOneUse() && CI->getParent() == PN->getIncomingBlock(I) &&
TLI->mayBeEmittedAsTailCall(CI) &&
attributesPermitTailCall(F, CI, RetI, *TLI))
} else {
SmallPtrSet<BasicBlock*, 4> VisitedBBs;
for (pred_iterator PI = pred_begin(BB), PE = pred_end(BB); PI != PE; ++PI) {
if (!VisitedBBs.insert(*PI).second)
BasicBlock::InstListType &InstList = (*PI)->getInstList();
BasicBlock::InstListType::reverse_iterator RI = InstList.rbegin();
BasicBlock::InstListType::reverse_iterator RE = InstList.rend();
do { ++RI; } while (RI != RE && isa<DbgInfoIntrinsic>(&*RI));
if (RI == RE)
CallInst *CI = dyn_cast<CallInst>(&*RI);
if (CI && CI->use_empty() && TLI->mayBeEmittedAsTailCall(CI) &&
attributesPermitTailCall(F, CI, RetI, *TLI))
bool Changed = false;
for (unsigned i = 0, e = TailCalls.size(); i != e; ++i) {
CallInst *CI = TailCalls[i];
CallSite CS(CI);
// Conservatively require the attributes of the call to match those of the
// return. Ignore noalias because it doesn't affect the call sequence.
AttributeList CalleeAttrs = CS.getAttributes();
if (AttrBuilder(CalleeAttrs, AttributeList::ReturnIndex)
.removeAttribute(Attribute::NoAlias) !=
AttrBuilder(CalleeAttrs, AttributeList::ReturnIndex)
// Make sure the call instruction is followed by an unconditional branch to
// the return block.
BasicBlock *CallBB = CI->getParent();
BranchInst *BI = dyn_cast<BranchInst>(CallBB->getTerminator());
if (!BI || !BI->isUnconditional() || BI->getSuccessor(0) != BB)
// Duplicate the return into CallBB.
(void)FoldReturnIntoUncondBranch(RetI, BB, CallBB);
ModifiedDT = Changed = true;
// If we eliminated all predecessors of the block, delete the block now.
if (Changed && !BB->hasAddressTaken() && pred_begin(BB) == pred_end(BB))
return Changed;
// Memory Optimization
namespace {
/// This is an extended version of TargetLowering::AddrMode
/// which holds actual Value*'s for register values.
struct ExtAddrMode : public TargetLowering::AddrMode {
Value *BaseReg = nullptr;
Value *ScaledReg = nullptr;
Value *OriginalValue = nullptr;
enum FieldName {
NoField = 0x00,
BaseRegField = 0x01,
BaseGVField = 0x02,
BaseOffsField = 0x04,
ScaledRegField = 0x08,
ScaleField = 0x10,
MultipleFields = 0xff
ExtAddrMode() = default;
void print(raw_ostream &OS) const;
void dump() const;
FieldName compare(const ExtAddrMode &other) {
// First check that the types are the same on each field, as differing types
// is something we can't cope with later on.
if (BaseReg && other.BaseReg &&
BaseReg->getType() != other.BaseReg->getType())
return MultipleFields;
if (BaseGV && other.BaseGV &&
BaseGV->getType() != other.BaseGV->getType())
return MultipleFields;
if (ScaledReg && other.ScaledReg &&
ScaledReg->getType() != other.ScaledReg->getType())
return MultipleFields;
// Check each field to see if it differs.
unsigned Result = NoField;
if (BaseReg != other.BaseReg)
Result |= BaseRegField;
if (BaseGV != other.BaseGV)
Result |= BaseGVField;
if (BaseOffs != other.BaseOffs)
Result |= BaseOffsField;
if (ScaledReg != other.ScaledReg)
Result |= ScaledRegField;
// Don't count 0 as being a different scale, because that actually means
// unscaled (which will already be counted by having no ScaledReg).
if (Scale && other.Scale && Scale != other.Scale)
Result |= ScaleField;
if (countPopulation(Result) > 1)
return MultipleFields;
return static_cast<FieldName>(Result);
// An AddrMode is trivial if it involves no calculation i.e. it is just a base
// with no offset.
bool isTrivial() {
// An AddrMode is (BaseGV + BaseReg + BaseOffs + ScaleReg * Scale) so it is
// trivial if at most one of these terms is nonzero, except that BaseGV and
// BaseReg both being zero actually means a null pointer value, which we
// consider to be 'non-zero' here.
return !BaseOffs && !Scale && !(BaseGV && BaseReg);
Value *GetFieldAsValue(FieldName Field, Type *IntPtrTy) {
switch (Field) {
return nullptr;
case BaseRegField:
return BaseReg;
case BaseGVField:
return BaseGV;
case ScaledRegField:
return ScaledReg;
case BaseOffsField:
return ConstantInt::get(IntPtrTy, BaseOffs);
void SetCombinedField(FieldName Field, Value *V,
const SmallVectorImpl<ExtAddrMode> &AddrModes) {
switch (Field) {
llvm_unreachable("Unhandled fields are expected to be rejected earlier");
case ExtAddrMode::BaseRegField:
BaseReg = V;
case ExtAddrMode::BaseGVField:
// A combined BaseGV is an Instruction, not a GlobalValue, so it goes
// in the BaseReg field.
assert(BaseReg == nullptr);
BaseReg = V;
BaseGV = nullptr;
case ExtAddrMode::ScaledRegField:
ScaledReg = V;
// If we have a mix of scaled and unscaled addrmodes then we want scale
// to be the scale and not zero.
if (!Scale)
for (const ExtAddrMode &AM : AddrModes)
if (AM.Scale) {
Scale = AM.Scale;
case ExtAddrMode::BaseOffsField:
// The offset is no longer a constant, so it goes in ScaledReg with a
// scale of 1.
assert(ScaledReg == nullptr);
ScaledReg = V;
Scale = 1;
BaseOffs = 0;
} // end anonymous namespace
#ifndef NDEBUG
static inline raw_ostream &operator<<(raw_ostream &OS, const ExtAddrMode &AM) {
return OS;
#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
void ExtAddrMode::print(raw_ostream &OS) const {
bool NeedPlus = false;
OS << "[";
if (BaseGV) {
OS << (NeedPlus ? " + " : "")
<< "GV:";
BaseGV->printAsOperand(OS, /*PrintType=*/false);
NeedPlus = true;
if (BaseOffs) {
OS << (NeedPlus ? " + " : "")
<< BaseOffs;
NeedPlus = true;
if (BaseReg) {
OS << (NeedPlus ? " + " : "")
<< "Base:";
BaseReg->printAsOperand(OS, /*PrintType=*/false);
NeedPlus = true;
if (Scale) {
OS << (NeedPlus ? " + " : "")
<< Scale << "*";
ScaledReg->printAsOperand(OS, /*PrintType=*/false);
OS << ']';
LLVM_DUMP_METHOD void ExtAddrMode::dump() const {
dbgs() << '\n';
namespace {
/// This class provides transaction based operation on the IR.
/// Every change made through this class is recorded in the internal state and
/// can be undone (rollback) until commit is called.
class TypePromotionTransaction {
/// This represents the common interface of the individual transaction.
/// Each class implements the logic for doing one specific modification on
/// the IR via the TypePromotionTransaction.
class TypePromotionAction {
/// The Instruction modified.
Instruction *Inst;
/// Constructor of the action.
/// The constructor performs the related action on the IR.
TypePromotionAction(Instruction *Inst) : Inst(Inst) {}
virtual ~TypePromotionAction() = default;
/// Undo the modification done by this action.
/// When this method is called, the IR must be in the same state as it was
/// before this action was applied.
/// \pre Undoing the action works if and only if the IR is in the exact same
/// state as it was directly after this action was applied.
virtual void undo() = 0;
/// Advocate every change made by this action.
/// When the results on the IR of the action are to be kept, it is important
/// to call this function, otherwise hidden information may be kept forever.
virtual void commit() {
// Nothing to be done, this action is not doing anything.
/// Utility to remember the position of an instruction.
class InsertionHandler {
/// Position of an instruction.
/// Either an instruction:
/// - Is the first in a basic block: BB is used.
/// - Has a previous instruction: PrevInst is used.
union {
Instruction *PrevInst;
BasicBlock *BB;
} Point;
/// Remember whether or not the instruction had a previous instruction.
bool HasPrevInstruction;
/// Record the position of \p Inst.
InsertionHandler(Instruction *Inst) {
BasicBlock::iterator It = Inst->getIterator();
HasPrevInstruction = (It != (Inst->getParent()->begin()));
if (HasPrevInstruction)
Point.PrevInst = &*--It;
Point.BB = Inst->getParent();
/// Insert \p Inst at the recorded position.
void insert(Instruction *Inst) {
if (HasPrevInstruction) {
if (Inst->getParent())
} else {
Instruction *Position = &*Point.BB->getFirstInsertionPt();
if (Inst->getParent())
/// Move an instruction before another.
class InstructionMoveBefore : public TypePromotionAction {
/// Original position of the instruction.
InsertionHandler Position;
/// Move \p Inst before \p Before.
InstructionMoveBefore(Instruction *Inst, Instruction *Before)
: TypePromotionAction(Inst), Position(Inst) {
LLVM_DEBUG(dbgs() << "Do: move: " << *Inst << "\nbefore: " << *Before
<< "\n");
/// Move the instruction back to its original position.
void undo() override {
LLVM_DEBUG(dbgs() << "Undo: moveBefore: " << *Inst << "\n");
/// Set the operand of an instruction with a new value.
class OperandSetter : public TypePromotionAction {
/// Original operand of the instruction.
Value *Origin;
/// Index of the modified instruction.
unsigned Idx;
/// Set \p Idx operand of \p Inst with \p NewVal.
OperandSetter(Instruction *Inst, unsigned Idx, Value *NewVal)
: TypePromotionAction(Inst), Idx(Idx) {
LLVM_DEBUG(dbgs() << "Do: setOperand: " << Idx << "\n"
<< "for:" << *Inst << "\n"
<< "with:" << *NewVal << "\n");
Origin = Inst->getOperand(Idx);
Inst->setOperand(Idx, NewVal);
/// Restore the original value of the instruction.
void undo() override {
LLVM_DEBUG(dbgs() << "Undo: setOperand:" << Idx << "\n"
<< "for: " << *Inst << "\n"
<< "with: " << *Origin << "\n");
Inst->setOperand(Idx, Origin);
/// Hide the operands of an instruction.
/// Do as if this instruction was not using any of its operands.
class OperandsHider : public TypePromotionAction {
/// The list of original operands.
SmallVector<Value *, 4> OriginalValues;
/// Remove \p Inst from the uses of the operands of \p Inst.
OperandsHider(Instruction *Inst) : TypePromotionAction(Inst) {
LLVM_DEBUG(dbgs() << "Do: OperandsHider: " << *Inst << "\n");
unsigned NumOpnds = Inst->getNumOperands();
for (unsigned It = 0; It < NumOpnds; ++It) {
// Save the current operand.
Value *Val = Inst->getOperand(It);
// Set a dummy one.
// We could use OperandSetter here, but that would imply an overhead
// that we are not willing to pay.
Inst->setOperand(It, UndefValue::get(Val->getType()));
/// Restore the original list of uses.
void undo() override {
LLVM_DEBUG(dbgs() << "Undo: OperandsHider: " << *Inst << "\n");
for (unsigned It = 0, EndIt = OriginalValues.size(); It != EndIt; ++It)
Inst->setOperand(It, OriginalValues[It]);
/// Build a truncate instruction.
class TruncBuilder : public TypePromotionAction {
Value *Val;
/// Build a truncate instruction of \p Opnd producing a \p Ty
/// result.
/// trunc Opnd to Ty.
TruncBuilder(Instruction *Opnd, Type *Ty) : TypePromotionAction(Opnd) {
IRBuilder<> Builder(Opnd);
Val = Builder.CreateTrunc(Opnd, Ty, "promoted");
LLVM_DEBUG(dbgs() << "Do: TruncBuilder: " << *Val << "\n");
/// Get the built value.
Value *getBuiltValue() { return Val; }
/// Remove the built instruction.
void undo() override {
LLVM_DEBUG(dbgs() << "Undo: TruncBuilder: " << *Val << "\n");
if (Instruction *IVal = dyn_cast<Instruction>(Val))
/// Build a sign extension instruction.
class SExtBuilder : public TypePromotionAction {
Value *Val;
/// Build a sign extension instruction of \p Opnd producing a \p Ty
/// result.
/// sext Opnd to Ty.
SExtBuilder(Instruction *InsertPt, Value *Opnd, Type *Ty)
: TypePromotionAction(InsertPt) {
IRBuilder<> Builder(InsertPt);
Val = Builder.CreateSExt(Opnd, Ty, "promoted");
LLVM_DEBUG(dbgs() << "Do: SExtBuilder: " << *Val << "\n");
/// Get the built value.
Value *getBuiltValue() { return Val; }
/// Remove the built instruction.
void undo() override {
LLVM_DEBUG(dbgs() << "Undo: SExtBuilder: " << *Val << "\n");
if (Instruction *IVal = dyn_cast<Instruction>(Val))
/// Build a zero extension instruction.
class ZExtBuilder : public TypePromotionAction {
Value *Val;
/// Build a zero extension instruction of \p Opnd producing a \p Ty
/// result.
/// zext Opnd to Ty.
ZExtBuilder(Instruction *InsertPt, Value *Opnd, Type *Ty)
: TypePromotionAction(InsertPt) {
IRBuilder<> Builder(InsertPt);
Val = Builder.CreateZExt(Opnd, Ty, "promoted");
LLVM_DEBUG(dbgs() << "Do: ZExtBuilder: " << *Val << "\n");
/// Get the built value.
Value *getBuiltValue() { return Val; }
/// Remove the built instruction.
void undo() override {
LLVM_DEBUG(dbgs() << "Undo: ZExtBuilder: " << *Val << "\n");
if (Instruction *IVal = dyn_cast<Instruction>(Val))
/// Mutate an instruction to another type.
class TypeMutator : public TypePromotionAction {
/// Record the original type.
Type *OrigTy;
/// Mutate the type of \p Inst into \p NewTy.
TypeMutator(Instruction *Inst, Type *NewTy)
: TypePromotionAction(Inst), OrigTy(Inst->getType()) {
LLVM_DEBUG(dbgs() << "Do: MutateType: " << *Inst << " with " << *NewTy
<< "\n");
/// Mutate the instruction back to its original type.
void undo() override {
LLVM_DEBUG(dbgs() << "Undo: MutateType: " << *Inst << " with " << *OrigTy
<< "\n");
/// Replace the uses of an instruction by another instruction.
class UsesReplacer : public TypePromotionAction {
/// Helper structure to keep track of the replaced uses.
struct InstructionAndIdx {
/// The instruction using the instruction.
Instruction *Inst;
/// The index where this instruction is used for Inst.
unsigned Idx;
InstructionAndIdx(Instruction *Inst, unsigned Idx)
: Inst(Inst), Idx(Idx) {}
/// Keep track of the original uses (pair Instruction, Index).
SmallVector<InstructionAndIdx, 4> OriginalUses;
using use_iterator = SmallVectorImpl<InstructionAndIdx>::iterator;
/// Replace all the use of \p Inst by \p New.
UsesReplacer(Instruction *Inst, Value *New) : TypePromotionAction(Inst) {
LLVM_DEBUG(dbgs() << "Do: UsersReplacer: " << *Inst << " with " << *New
<< "\n");
// Record the original uses.
for (Use &U : Inst->uses()) {
Instruction *UserI = cast<Instruction>(U.getUser());
OriginalUses.push_back(InstructionAndIdx(UserI, U.getOperandNo()));
// Now, we can replace the uses.
/// Reassign the original uses of Inst to Inst.
void undo() override {
LLVM_DEBUG(dbgs() << "Undo: UsersReplacer: " << *Inst << "\n");
for (use_iterator UseIt = OriginalUses.begin(),
EndIt = OriginalUses.end();
UseIt != EndIt; ++UseIt) {
UseIt->Inst->setOperand(UseIt->Idx, Inst);
/// Remove an instruction from the IR.
class InstructionRemover : public TypePromotionAction {
/// Original position of the instruction.
InsertionHandler Inserter;
/// Helper structure to hide all the link to the instruction. In other
/// words, this helps to do as if the instruction was removed.
OperandsHider Hider;
/// Keep track of the uses replaced, if any.
UsesReplacer *Replacer = nullptr;
/// Keep track of instructions removed.
SetOfInstrs &RemovedInsts;
/// Remove all reference of \p Inst and optionally replace all its
/// uses with New.
/// \p RemovedInsts Keep track of the instructions removed by this Action.
/// \pre If !Inst->use_empty(), then New != nullptr
InstructionRemover(Instruction *Inst, SetOfInstrs &RemovedInsts,
Value *New = nullptr)
: TypePromotionAction(Inst), Inserter(Inst), Hider(Inst),
RemovedInsts(RemovedInsts) {
if (New)
Replacer = new UsesReplacer(Inst, New);
LLVM_DEBUG(dbgs() << "Do: InstructionRemover: " << *Inst << "\n");
/// The instructions removed here will be freed after completing
/// optimizeBlock() for all blocks as we need to keep track of the
/// removed instructions during promotion.
~InstructionRemover() override { delete Replacer; }
/// Resurrect the instruction and reassign it to the proper uses if
/// new value was provided when build this action.
void undo() override {
LLVM_DEBUG(dbgs() << "Undo: InstructionRemover: " << *Inst << "\n");
if (Replacer)
/// Restoration point.
/// The restoration point is a pointer to an action instead of an iterator
/// because the iterator may be invalidated but not the pointer.
using ConstRestorationPt = const TypePromotionAction *;
TypePromotionTransaction(SetOfInstrs &RemovedInsts)
: RemovedInsts(RemovedInsts) {}
/// Advocate every changes made in that transaction.
void commit();
/// Undo all the changes made after the given point.
void rollback(ConstRestorationPt Point);
/// Get the current restoration point.
ConstRestorationPt getRestorationPoint() const;
/// \name API for IR modification with state keeping to support rollback.
/// @{
/// Same as Instruction::setOperand.
void setOperand(Instruction *Inst, unsigned Idx, Value *NewVal);
/// Same as Instruction::eraseFromParent.
void eraseInstruction(Instruction *Inst, Value *NewVal = nullptr);
/// Same as Value::replaceAllUsesWith.
void replaceAllUsesWith(Instruction *Inst, Value *New);
/// Same as Value::mutateType.
void mutateType(Instruction *Inst, Type *NewTy);
/// Same as IRBuilder::createTrunc.
Value *createTrunc(Instruction *Opnd, Type *Ty);
/// Same as IRBuilder::createSExt.
Value *createSExt(Instruction *Inst, Value *Opnd, Type *Ty);
/// Same as IRBuilder::createZExt.
Value *createZExt(Instruction *Inst, Value *Opnd, Type *Ty);
/// Same as Instruction::moveBefore.
void moveBefore(Instruction *Inst, Instruction *Before);
/// @}
/// The ordered list of actions made so far.
SmallVector<std::unique_ptr<TypePromotionAction>, 16> Actions;
using CommitPt = SmallVectorImpl<std::unique_ptr<TypePromotionAction>>::iterator;
SetOfInstrs &RemovedInsts;
} // end anonymous namespace
void TypePromotionTransaction::setOperand(Instruction *Inst, unsigned Idx,
Value *NewVal) {
Inst, Idx, NewVal));
void TypePromotionTransaction::eraseInstruction(Instruction *Inst,
Value *NewVal) {
Inst, RemovedInsts, NewVal));
void TypePromotionTransaction::replaceAllUsesWith(Instruction *Inst,
Value *New) {
llvm::make_unique<TypePromotionTransaction::UsesReplacer>(Inst, New));
void TypePromotionTransaction::mutateType(Instruction *Inst, Type *NewTy) {
llvm::make_unique<TypePromotionTransaction::TypeMutator>(Inst, NewTy));
Value *TypePromotionTransaction::createTrunc(Instruction *Opnd,
Type *Ty) {
std::unique_ptr<TruncBuilder> Ptr(new TruncBuilder(Opnd, Ty));
Value *Val = Ptr->getBuiltValue();
return Val;
Value *TypePromotionTransaction::createSExt(Instruction *Inst,
Value *Opnd, Type *Ty) {
std::unique_ptr<SExtBuilder> Ptr(new SExtBuilder(Inst, Opnd, Ty));
Value *Val = Ptr->getBuiltValue();
return Val;
Value *TypePromotionTransaction::createZExt(Instruction *Inst,
Value *Opnd, Type *Ty) {
std::unique_ptr<ZExtBuilder> Ptr(new ZExtBuilder(Inst, Opnd, Ty));
Value *Val = Ptr->getBuiltValue();
return Val;
void TypePromotionTransaction::moveBefore(Instruction *Inst,
Instruction *Before) {
Inst, Before));
TypePromotionTransaction::getRestorationPoint() const {
return !Actions.empty() ? Actions.back().get() : nullptr;
void TypePromotionTransaction::commit() {
for (CommitPt It = Actions.begin(), EndIt = Actions.end(); It != EndIt;
void TypePromotionTransaction::rollback(
TypePromotionTransaction::ConstRestorationPt Point) {
while (!Actions.empty() && Point != Actions.back().get()) {
std::unique_ptr<TypePromotionAction> Curr = Actions.pop_back_val();
namespace {
/// A helper class for matching addressing modes.
/// This encapsulates the logic for matching the target-legal addressing modes.
class AddressingModeMatcher {
SmallVectorImpl<Instruction*> &AddrModeInsts;
const TargetLowering &TLI;
const TargetRegisterInfo &TRI;
const DataLayout &DL;
/// AccessTy/MemoryInst - This is the type for the access (e.g. double) and
/// the memory instruction that we're computing this address for.
Type *AccessTy;
unsigned AddrSpace;
Instruction *MemoryInst;
/// This is the addressing mode that we're building up. This is
/// part of the return value of this addressing mode matching stuff.
ExtAddrMode &AddrMode;
/// The instructions inserted by other CodeGenPrepare optimizations.
const SetOfInstrs &InsertedInsts;
/// A map from the instructions to their type before promotion.
InstrToOrigTy &PromotedInsts;
/// The ongoing transaction where every action should be registered.
TypePromotionTransaction &TPT;
// A GEP which has too large offset to be folded into the addressing mode.
std::pair<AssertingVH<GetElementPtrInst>, int64_t> &LargeOffsetGEP;
/// This is set to true when we should not do profitability checks.
/// When true, IsProfitableToFoldIntoAddressingMode always returns true.
bool IgnoreProfitability;
SmallVectorImpl<Instruction *> &AMI, const TargetLowering &TLI,
const TargetRegisterInfo &TRI, Type *AT, unsigned AS, Instruction *MI,
ExtAddrMode &AM, const SetOfInstrs &InsertedInsts,
InstrToOrigTy &PromotedInsts, TypePromotionTransaction &TPT,
std::pair<AssertingVH<GetElementPtrInst>, int64_t> &LargeOffsetGEP)
: AddrModeInsts(AMI), TLI(TLI), TRI(TRI),
DL(MI->getModule()->getDataLayout()), AccessTy(AT), AddrSpace(AS),
MemoryInst(MI), AddrMode(AM), InsertedInsts(InsertedInsts),
PromotedInsts(PromotedInsts), TPT(TPT), LargeOffsetGEP(LargeOffsetGEP) {
IgnoreProfitability = false;
/// Find the maximal addressing mode that a load/store of V can fold,
/// give an access type of AccessTy. This returns a list of involved
/// instructions in AddrModeInsts.
/// \p InsertedInsts The instructions inserted by other CodeGenPrepare
/// optimizations.
/// \p PromotedInsts maps the instructions to their type before promotion.
/// \p The ongoing transaction where every action should be registered.
static ExtAddrMode
Match(Value *V, Type *AccessTy, unsigned AS, Instruction *MemoryInst,
SmallVectorImpl<Instruction *> &AddrModeInsts,
const TargetLowering &TLI, const TargetRegisterInfo &TRI,
const SetOfInstrs &InsertedInsts, InstrToOrigTy &PromotedInsts,
TypePromotionTransaction &TPT,
std::pair<AssertingVH<GetElementPtrInst>, int64_t> &LargeOffsetGEP) {
ExtAddrMode Result;
bool Success = AddressingModeMatcher(AddrModeInsts, TLI, TRI, AccessTy, AS,
MemoryInst, Result, InsertedInsts,
PromotedInsts, TPT, LargeOffsetGEP)
.matchAddr(V, 0);
(void)Success; assert(Success && "Couldn't select *anything*?");
return Result;
bool matchScaledValue(Value *ScaleReg, int64_t Scale, unsigned Depth);
bool matchAddr(Value *Addr, unsigned Depth);
bool matchOperationAddr(User *AddrInst, unsigned Opcode, unsigned Depth,
bool *MovedAway = nullptr);
bool isProfitableToFoldIntoAddressingMode(Instruction *I,
ExtAddrMode &AMBefore,
ExtAddrMode &AMAfter);
bool valueAlreadyLiveAtInst(Value *Val, Value *KnownLive1, Value *KnownLive2);
bool isPromotionProfitable(unsigned NewCost, unsigned OldCost,
Value *PromotedOperand) const;
/// Keep track of simplification of Phi nodes.
/// Accept the set of all phi nodes and erase phi node from this set
/// if it is simplified.
class SimplificationTracker {
DenseMap<Value *, Value *> Storage;
const SimplifyQuery &SQ;
// Tracks newly created Phi nodes. We use a SetVector to get deterministic
// order when iterating over the set in MatchPhiSet.
SmallSetVector<PHINode *, 32> AllPhiNodes;
// Tracks newly created Select nodes.
SmallPtrSet<SelectInst *, 32> AllSelectNodes;
SimplificationTracker(const SimplifyQuery &sq)
: SQ(sq) {}
Value *Get(Value *V) {
do {
auto SV = Storage.find(V);
if (SV == Storage.end())
return V;
V = SV->second;
} while (true);
Value *Simplify(Value *Val) {
SmallVector<Value *, 32> WorkList;
SmallPtrSet<Value *, 32> Visited;
while (!WorkList.empty()) {
auto P = WorkList.pop_back_val();
if (!Visited.insert(P).second)
if (auto *PI = dyn_cast<Instruction>(P))
if (Value *V = SimplifyInstruction(cast<Instruction>(PI), SQ)) {
for (auto *U : PI->users())
Put(PI, V);
if (auto *PHI = dyn_cast<PHINode>(PI))
if (auto *Select = dyn_cast<SelectInst>(PI))
return Get(Val);
void Put(Value *From, Value *To) {
Storage.insert({ From, To });
void ReplacePhi(PHINode *From, PHINode *To) {
Value* OldReplacement = Get(From);
while (OldReplacement != From) {
From = To;
To = dyn_cast<PHINode>(OldReplacement);
OldReplacement = Get(From);
assert(Get(To) == To && "Replacement PHI node is already replaced.");
Put(From, To);
SmallSetVector<PHINode *, 32>& newPhiNodes() { return AllPhiNodes; }
void insertNewPhi(PHINode *PN) { AllPhiNodes.insert(PN); }
void insertNewSelect(SelectInst *SI) { AllSelectNodes.insert(SI); }
unsigned countNewPhiNodes() const { return AllPhiNodes.size(); }
unsigned countNewSelectNodes() const { return AllSelectNodes.size(); }
void destroyNewNodes(Type *CommonType) {
// For safe erasing, replace the uses with dummy value first.
auto Dummy = UndefValue::get(CommonType);
for (auto I : AllPhiNodes) {
for (auto I : AllSelectNodes) {
/// A helper class for combining addressing modes.
class AddressingModeCombiner {
typedef std::pair<Value *, BasicBlock *> ValueInBB;
typedef DenseMap<ValueInBB, Value *> FoldAddrToValueMapping;
typedef std::pair<PHINode *, PHINode *> PHIPair;
/// The addressing modes we've collected.
SmallVector<ExtAddrMode, 16> AddrModes;
/// The field in which the AddrModes differ, when we have more than one.
ExtAddrMode::FieldName DifferentField = ExtAddrMode::NoField;
/// Are the AddrModes that we have all just equal to their original values?
bool AllAddrModesTrivial = true;
/// Common Type for all different fields in addressing modes.
Type *CommonType;
/// SimplifyQuery for simplifyInstruction utility.
const SimplifyQuery &SQ;
/// Original Address.
ValueInBB Original;
AddressingModeCombiner(const SimplifyQuery &_SQ, ValueInBB OriginalValue)
: CommonType(nullptr), SQ(_SQ), Original(OriginalValue) {}
/// Get the combined AddrMode
const ExtAddrMode &getAddrMode() const {
return AddrModes[0];
/// Add a new AddrMode if it's compatible with the AddrModes we already
/// have.
/// \return True iff we succeeded in doing so.
bool addNewAddrMode(ExtAddrMode &NewAddrMode) {
// Take note of if we have any non-trivial AddrModes, as we need to detect
// when all AddrModes are trivial as then we would introduce a phi or select
// which just duplicates what's already there.
AllAddrModesTrivial = AllAddrModesTrivial && NewAddrMode.isTrivial();
// If this is the first addrmode then everything is fine.
if (AddrModes.empty()) {
return true;
// Figure out how different this is from the other address modes, which we
// can do just by comparing against the first one given that we only care
// about the cumulative difference.
ExtAddrMode::FieldName ThisDifferentField =
if (DifferentField == ExtAddrMode::NoField)
DifferentField = ThisDifferentField;
else if (DifferentField != ThisDifferentField)
DifferentField = ExtAddrMode::MultipleFields;
// If NewAddrMode differs in more than one dimension we cannot handle it.
bool CanHandle = DifferentField != ExtAddrMode::MultipleFields;
// If Scale Field is different then we reject.