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//===- SIAnnotateControlFlow.cpp ------------------------------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
/// \file
/// Annotates the control flow with hardware specific intrinsics.
//
//===----------------------------------------------------------------------===//
#include "AMDGPU.h"
#include "llvm/ADT/DepthFirstIterator.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/Analysis/DivergenceAnalysis.h"
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/Transforms/Utils/Local.h"
#include "llvm/IR/BasicBlock.h"
#include "llvm/IR/CFG.h"
#include "llvm/IR/Constant.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/DerivedTypes.h"
#include "llvm/IR/Dominators.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/Instruction.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/Intrinsics.h"
#include "llvm/IR/Module.h"
#include "llvm/IR/Type.h"
#include "llvm/IR/ValueHandle.h"
#include "llvm/Pass.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
#include <cassert>
#include <utility>
using namespace llvm;
#define DEBUG_TYPE "si-annotate-control-flow"
namespace {
// Complex types used in this pass
using StackEntry = std::pair<BasicBlock *, Value *>;
using StackVector = SmallVector<StackEntry, 16>;
class SIAnnotateControlFlow : public FunctionPass {
DivergenceAnalysis *DA;
Type *Boolean;
Type *Void;
Type *Int64;
Type *ReturnStruct;
ConstantInt *BoolTrue;
ConstantInt *BoolFalse;
UndefValue *BoolUndef;
Constant *Int64Zero;
Function *If;
Function *Else;
Function *Break;
Function *IfBreak;
Function *ElseBreak;
Function *Loop;
Function *EndCf;
DominatorTree *DT;
StackVector Stack;
LoopInfo *LI;
bool isUniform(BranchInst *T);
bool isTopOfStack(BasicBlock *BB);
Value *popSaved();
void push(BasicBlock *BB, Value *Saved);
bool isElse(PHINode *Phi);
void eraseIfUnused(PHINode *Phi);
void openIf(BranchInst *Term);
void insertElse(BranchInst *Term);
Value *
handleLoopCondition(Value *Cond, PHINode *Broken, llvm::Loop *L,
BranchInst *Term,
SmallVectorImpl<WeakTrackingVH> &LoopPhiConditions);
void handleLoop(BranchInst *Term);
void closeControlFlow(BasicBlock *BB);
public:
static char ID;
SIAnnotateControlFlow() : FunctionPass(ID) {}
bool doInitialization(Module &M) override;
bool runOnFunction(Function &F) override;
StringRef getPassName() const override { return "SI annotate control flow"; }
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.addRequired<LoopInfoWrapperPass>();
AU.addRequired<DominatorTreeWrapperPass>();
AU.addRequired<DivergenceAnalysis>();
AU.addPreserved<DominatorTreeWrapperPass>();
FunctionPass::getAnalysisUsage(AU);
}
};
} // end anonymous namespace
INITIALIZE_PASS_BEGIN(SIAnnotateControlFlow, DEBUG_TYPE,
"Annotate SI Control Flow", false, false)
INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
INITIALIZE_PASS_DEPENDENCY(DivergenceAnalysis)
INITIALIZE_PASS_END(SIAnnotateControlFlow, DEBUG_TYPE,
"Annotate SI Control Flow", false, false)
char SIAnnotateControlFlow::ID = 0;
/// Initialize all the types and constants used in the pass
bool SIAnnotateControlFlow::doInitialization(Module &M) {
LLVMContext &Context = M.getContext();
Void = Type::getVoidTy(Context);
Boolean = Type::getInt1Ty(Context);
Int64 = Type::getInt64Ty(Context);
ReturnStruct = StructType::get(Boolean, Int64);
BoolTrue = ConstantInt::getTrue(Context);
BoolFalse = ConstantInt::getFalse(Context);
BoolUndef = UndefValue::get(Boolean);
Int64Zero = ConstantInt::get(Int64, 0);
If = Intrinsic::getDeclaration(&M, Intrinsic::amdgcn_if);
Else = Intrinsic::getDeclaration(&M, Intrinsic::amdgcn_else);
Break = Intrinsic::getDeclaration(&M, Intrinsic::amdgcn_break);
IfBreak = Intrinsic::getDeclaration(&M, Intrinsic::amdgcn_if_break);
ElseBreak = Intrinsic::getDeclaration(&M, Intrinsic::amdgcn_else_break);
Loop = Intrinsic::getDeclaration(&M, Intrinsic::amdgcn_loop);
EndCf = Intrinsic::getDeclaration(&M, Intrinsic::amdgcn_end_cf);
return false;
}
/// Is the branch condition uniform or did the StructurizeCFG pass
/// consider it as such?
bool SIAnnotateControlFlow::isUniform(BranchInst *T) {
return DA->isUniform(T->getCondition()) ||
T->getMetadata("structurizecfg.uniform") != nullptr;
}
/// Is BB the last block saved on the stack ?
bool SIAnnotateControlFlow::isTopOfStack(BasicBlock *BB) {
return !Stack.empty() && Stack.back().first == BB;
}
/// Pop the last saved value from the control flow stack
Value *SIAnnotateControlFlow::popSaved() {
return Stack.pop_back_val().second;
}
/// Push a BB and saved value to the control flow stack
void SIAnnotateControlFlow::push(BasicBlock *BB, Value *Saved) {
Stack.push_back(std::make_pair(BB, Saved));
}
/// Can the condition represented by this PHI node treated like
/// an "Else" block?
bool SIAnnotateControlFlow::isElse(PHINode *Phi) {
BasicBlock *IDom = DT->getNode(Phi->getParent())->getIDom()->getBlock();
for (unsigned i = 0, e = Phi->getNumIncomingValues(); i != e; ++i) {
if (Phi->getIncomingBlock(i) == IDom) {
if (Phi->getIncomingValue(i) != BoolTrue)
return false;
} else {
if (Phi->getIncomingValue(i) != BoolFalse)
return false;
}
}
return true;
}
// Erase "Phi" if it is not used any more
void SIAnnotateControlFlow::eraseIfUnused(PHINode *Phi) {
if (RecursivelyDeleteDeadPHINode(Phi)) {
LLVM_DEBUG(dbgs() << "Erased unused condition phi\n");
}
}
/// Open a new "If" block
void SIAnnotateControlFlow::openIf(BranchInst *Term) {
if (isUniform(Term))
return;
Value *Ret = CallInst::Create(If, Term->getCondition(), "", Term);
Term->setCondition(ExtractValueInst::Create(Ret, 0, "", Term));
push(Term->getSuccessor(1), ExtractValueInst::Create(Ret, 1, "", Term));
}
/// Close the last "If" block and open a new "Else" block
void SIAnnotateControlFlow::insertElse(BranchInst *Term) {
if (isUniform(Term)) {
return;
}
Value *Ret = CallInst::Create(Else, popSaved(), "", Term);
Term->setCondition(ExtractValueInst::Create(Ret, 0, "", Term));
push(Term->getSuccessor(1), ExtractValueInst::Create(Ret, 1, "", Term));
}
/// Recursively handle the condition leading to a loop
Value *SIAnnotateControlFlow::handleLoopCondition(
Value *Cond, PHINode *Broken, llvm::Loop *L, BranchInst *Term,
SmallVectorImpl<WeakTrackingVH> &LoopPhiConditions) {
// Only search through PHI nodes which are inside the loop. If we try this
// with PHI nodes that are outside of the loop, we end up inserting new PHI
// nodes outside of the loop which depend on values defined inside the loop.
// This will break the module with
// 'Instruction does not dominate all users!' errors.
PHINode *Phi = nullptr;
if ((Phi = dyn_cast<PHINode>(Cond)) && L->contains(Phi)) {
BasicBlock *Parent = Phi->getParent();
PHINode *NewPhi = PHINode::Create(Int64, 0, "loop.phi", &Parent->front());
Value *Ret = NewPhi;
// Handle all non-constant incoming values first
for (unsigned i = 0, e = Phi->getNumIncomingValues(); i != e; ++i) {
Value *Incoming = Phi->getIncomingValue(i);
BasicBlock *From = Phi->getIncomingBlock(i);
if (isa<ConstantInt>(Incoming)) {
NewPhi->addIncoming(Broken, From);
continue;
}
Phi->setIncomingValue(i, BoolFalse);
Value *PhiArg = handleLoopCondition(Incoming, Broken, L,
Term, LoopPhiConditions);
NewPhi->addIncoming(PhiArg, From);
}
BasicBlock *IDom = DT->getNode(Parent)->getIDom()->getBlock();
for (unsigned i = 0, e = Phi->getNumIncomingValues(); i != e; ++i) {
Value *Incoming = Phi->getIncomingValue(i);
if (Incoming != BoolTrue)
continue;
BasicBlock *From = Phi->getIncomingBlock(i);
if (From == IDom) {
// We're in the following situation:
// IDom/From
// | \
// | If-block
// | /
// Parent
// where we want to break out of the loop if the If-block is not taken.
// Due to the depth-first traversal, there should be an end.cf
// intrinsic in Parent, and we insert an else.break before it.
//
// Note that the end.cf need not be the first non-phi instruction
// of parent, particularly when we're dealing with a multi-level
// break, but it should occur within a group of intrinsic calls
// at the beginning of the block.
CallInst *OldEnd = dyn_cast<CallInst>(Parent->getFirstInsertionPt());
while (OldEnd && OldEnd->getCalledFunction() != EndCf)
OldEnd = dyn_cast<CallInst>(OldEnd->getNextNode());
if (OldEnd && OldEnd->getCalledFunction() == EndCf) {
Value *Args[] = { OldEnd->getArgOperand(0), NewPhi };
Ret = CallInst::Create(ElseBreak, Args, "", OldEnd);
continue;
}
}
TerminatorInst *Insert = From->getTerminator();
Value *PhiArg = CallInst::Create(Break, Broken, "", Insert);
NewPhi->setIncomingValue(i, PhiArg);
}
LoopPhiConditions.push_back(WeakTrackingVH(Phi));
return Ret;
}
if (Instruction *Inst = dyn_cast<Instruction>(Cond)) {
BasicBlock *Parent = Inst->getParent();
Instruction *Insert;
if (L->contains(Inst)) {
Insert = Parent->getTerminator();
} else {
Insert = L->getHeader()->getFirstNonPHIOrDbgOrLifetime();
}
Value *Args[] = { Cond, Broken };
return CallInst::Create(IfBreak, Args, "", Insert);
}
// Insert IfBreak in the loop header TERM for constant COND other than true.
if (isa<Constant>(Cond)) {
Instruction *Insert = Cond == BoolTrue ?
Term : L->getHeader()->getTerminator();
Value *Args[] = { Cond, Broken };
return CallInst::Create(IfBreak, Args, "", Insert);
}
llvm_unreachable("Unhandled loop condition!");
}
/// Handle a back edge (loop)
void SIAnnotateControlFlow::handleLoop(BranchInst *Term) {
if (isUniform(Term))
return;
BasicBlock *BB = Term->getParent();
llvm::Loop *L = LI->getLoopFor(BB);
if (!L)
return;
BasicBlock *Target = Term->getSuccessor(1);
PHINode *Broken = PHINode::Create(Int64, 0, "phi.broken", &Target->front());
SmallVector<WeakTrackingVH, 8> LoopPhiConditions;
Value *Cond = Term->getCondition();
Term->setCondition(BoolTrue);
Value *Arg = handleLoopCondition(Cond, Broken, L, Term, LoopPhiConditions);
for (BasicBlock *Pred : predecessors(Target))
Broken->addIncoming(Pred == BB ? Arg : Int64Zero, Pred);
Term->setCondition(CallInst::Create(Loop, Arg, "", Term));
for (WeakTrackingVH Val : llvm::reverse(LoopPhiConditions)) {
if (PHINode *Cond = cast_or_null<PHINode>(Val))
eraseIfUnused(Cond);
}
push(Term->getSuccessor(0), Arg);
}
/// Close the last opened control flow
void SIAnnotateControlFlow::closeControlFlow(BasicBlock *BB) {
llvm::Loop *L = LI->getLoopFor(BB);
assert(Stack.back().first == BB);
if (L && L->getHeader() == BB) {
// We can't insert an EndCF call into a loop header, because it will
// get executed on every iteration of the loop, when it should be
// executed only once before the loop.
SmallVector <BasicBlock *, 8> Latches;
L->getLoopLatches(Latches);
SmallVector<BasicBlock *, 2> Preds;
for (BasicBlock *Pred : predecessors(BB)) {
if (!is_contained(Latches, Pred))
Preds.push_back(Pred);
}
BB = SplitBlockPredecessors(BB, Preds, "endcf.split", DT, LI, false);
}
Value *Exec = popSaved();
Instruction *FirstInsertionPt = &*BB->getFirstInsertionPt();
if (!isa<UndefValue>(Exec) && !isa<UnreachableInst>(FirstInsertionPt))
CallInst::Create(EndCf, Exec, "", FirstInsertionPt);
}
/// Annotate the control flow with intrinsics so the backend can
/// recognize if/then/else and loops.
bool SIAnnotateControlFlow::runOnFunction(Function &F) {
DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
DA = &getAnalysis<DivergenceAnalysis>();
for (df_iterator<BasicBlock *> I = df_begin(&F.getEntryBlock()),
E = df_end(&F.getEntryBlock()); I != E; ++I) {
BasicBlock *BB = *I;
BranchInst *Term = dyn_cast<BranchInst>(BB->getTerminator());
if (!Term || Term->isUnconditional()) {
if (isTopOfStack(BB))
closeControlFlow(BB);
continue;
}
if (I.nodeVisited(Term->getSuccessor(1))) {
if (isTopOfStack(BB))
closeControlFlow(BB);
handleLoop(Term);
continue;
}
if (isTopOfStack(BB)) {
PHINode *Phi = dyn_cast<PHINode>(Term->getCondition());
if (Phi && Phi->getParent() == BB && isElse(Phi)) {
insertElse(Term);
eraseIfUnused(Phi);
continue;
}
closeControlFlow(BB);
}
openIf(Term);
}
if (!Stack.empty()) {
// CFG was probably not structured.
report_fatal_error("failed to annotate CFG");
}
return true;
}
/// Create the annotation pass
FunctionPass *llvm::createSIAnnotateControlFlowPass() {
return new SIAnnotateControlFlow();
}