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//===- Dominators.cpp - Dominator Calculation -----------------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements simple dominator construction algorithms for finding
// forward dominators. Postdominators are available in libanalysis, but are not
// included in libvmcore, because it's not needed. Forward dominators are
// needed to support the Verifier pass.
//
//===----------------------------------------------------------------------===//
#include "llvm/IR/Dominators.h"
#include "llvm/ADT/DepthFirstIterator.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/Config/llvm-config.h"
#include "llvm/IR/CFG.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/PassManager.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/GenericDomTreeConstruction.h"
#include "llvm/Support/raw_ostream.h"
#include <algorithm>
using namespace llvm;
bool llvm::VerifyDomInfo = false;
static cl::opt<bool, true>
VerifyDomInfoX("verify-dom-info", cl::location(VerifyDomInfo), cl::Hidden,
cl::desc("Verify dominator info (time consuming)"));
#ifdef EXPENSIVE_CHECKS
static constexpr bool ExpensiveChecksEnabled = true;
#else
static constexpr bool ExpensiveChecksEnabled = false;
#endif
bool BasicBlockEdge::isSingleEdge() const {
const TerminatorInst *TI = Start->getTerminator();
unsigned NumEdgesToEnd = 0;
for (unsigned int i = 0, n = TI->getNumSuccessors(); i < n; ++i) {
if (TI->getSuccessor(i) == End)
++NumEdgesToEnd;
if (NumEdgesToEnd >= 2)
return false;
}
assert(NumEdgesToEnd == 1);
return true;
}
//===----------------------------------------------------------------------===//
// DominatorTree Implementation
//===----------------------------------------------------------------------===//
//
// Provide public access to DominatorTree information. Implementation details
// can be found in Dominators.h, GenericDomTree.h, and
// GenericDomTreeConstruction.h.
//
//===----------------------------------------------------------------------===//
template class llvm::DomTreeNodeBase<BasicBlock>;
template class llvm::DominatorTreeBase<BasicBlock, false>; // DomTreeBase
template class llvm::DominatorTreeBase<BasicBlock, true>; // PostDomTreeBase
template struct llvm::DomTreeBuilder::Update<BasicBlock *>;
template void llvm::DomTreeBuilder::Calculate<DomTreeBuilder::BBDomTree>(
DomTreeBuilder::BBDomTree &DT);
template void llvm::DomTreeBuilder::Calculate<DomTreeBuilder::BBPostDomTree>(
DomTreeBuilder::BBPostDomTree &DT);
template void llvm::DomTreeBuilder::InsertEdge<DomTreeBuilder::BBDomTree>(
DomTreeBuilder::BBDomTree &DT, BasicBlock *From, BasicBlock *To);
template void llvm::DomTreeBuilder::InsertEdge<DomTreeBuilder::BBPostDomTree>(
DomTreeBuilder::BBPostDomTree &DT, BasicBlock *From, BasicBlock *To);
template void llvm::DomTreeBuilder::DeleteEdge<DomTreeBuilder::BBDomTree>(
DomTreeBuilder::BBDomTree &DT, BasicBlock *From, BasicBlock *To);
template void llvm::DomTreeBuilder::DeleteEdge<DomTreeBuilder::BBPostDomTree>(
DomTreeBuilder::BBPostDomTree &DT, BasicBlock *From, BasicBlock *To);
template void llvm::DomTreeBuilder::ApplyUpdates<DomTreeBuilder::BBDomTree>(
DomTreeBuilder::BBDomTree &DT, DomTreeBuilder::BBUpdates);
template void llvm::DomTreeBuilder::ApplyUpdates<DomTreeBuilder::BBPostDomTree>(
DomTreeBuilder::BBPostDomTree &DT, DomTreeBuilder::BBUpdates);
template bool llvm::DomTreeBuilder::Verify<DomTreeBuilder::BBDomTree>(
const DomTreeBuilder::BBDomTree &DT,
DomTreeBuilder::BBDomTree::VerificationLevel VL);
template bool llvm::DomTreeBuilder::Verify<DomTreeBuilder::BBPostDomTree>(
const DomTreeBuilder::BBPostDomTree &DT,
DomTreeBuilder::BBPostDomTree::VerificationLevel VL);
bool DominatorTree::invalidate(Function &F, const PreservedAnalyses &PA,
FunctionAnalysisManager::Invalidator &) {
// Check whether the analysis, all analyses on functions, or the function's
// CFG have been preserved.
auto PAC = PA.getChecker<DominatorTreeAnalysis>();
return !(PAC.preserved() || PAC.preservedSet<AllAnalysesOn<Function>>() ||
PAC.preservedSet<CFGAnalyses>());
}
// dominates - Return true if Def dominates a use in User. This performs
// the special checks necessary if Def and User are in the same basic block.
// Note that Def doesn't dominate a use in Def itself!
bool DominatorTree::dominates(const Instruction *Def,
const Instruction *User) const {
const BasicBlock *UseBB = User->getParent();
const BasicBlock *DefBB = Def->getParent();
// Any unreachable use is dominated, even if Def == User.
if (!isReachableFromEntry(UseBB))
return true;
// Unreachable definitions don't dominate anything.
if (!isReachableFromEntry(DefBB))
return false;
// An instruction doesn't dominate a use in itself.
if (Def == User)
return false;
// The value defined by an invoke dominates an instruction only if it
// dominates every instruction in UseBB.
// A PHI is dominated only if the instruction dominates every possible use in
// the UseBB.
if (isa<InvokeInst>(Def) || isa<PHINode>(User))
return dominates(Def, UseBB);
if (DefBB != UseBB)
return dominates(DefBB, UseBB);
// Loop through the basic block until we find Def or User.
BasicBlock::const_iterator I = DefBB->begin();
for (; &*I != Def && &*I != User; ++I)
/*empty*/;
return &*I == Def;
}
// true if Def would dominate a use in any instruction in UseBB.
// note that dominates(Def, Def->getParent()) is false.
bool DominatorTree::dominates(const Instruction *Def,
const BasicBlock *UseBB) const {
const BasicBlock *DefBB = Def->getParent();
// Any unreachable use is dominated, even if DefBB == UseBB.
if (!isReachableFromEntry(UseBB))
return true;
// Unreachable definitions don't dominate anything.
if (!isReachableFromEntry(DefBB))
return false;
if (DefBB == UseBB)
return false;
// Invoke results are only usable in the normal destination, not in the
// exceptional destination.
if (const auto *II = dyn_cast<InvokeInst>(Def)) {
BasicBlock *NormalDest = II->getNormalDest();
BasicBlockEdge E(DefBB, NormalDest);
return dominates(E, UseBB);
}
return dominates(DefBB, UseBB);
}
bool DominatorTree::dominates(const BasicBlockEdge &BBE,
const BasicBlock *UseBB) const {
// If the BB the edge ends in doesn't dominate the use BB, then the
// edge also doesn't.
const BasicBlock *Start = BBE.getStart();
const BasicBlock *End = BBE.getEnd();
if (!dominates(End, UseBB))
return false;
// Simple case: if the end BB has a single predecessor, the fact that it
// dominates the use block implies that the edge also does.
if (End->getSinglePredecessor())
return true;
// The normal edge from the invoke is critical. Conceptually, what we would
// like to do is split it and check if the new block dominates the use.
// With X being the new block, the graph would look like:
//
// DefBB
// /\ . .
// / \ . .
// / \ . .
// / \ | |
// A X B C
// | \ | /
// . \|/
// . NormalDest
// .
//
// Given the definition of dominance, NormalDest is dominated by X iff X
// dominates all of NormalDest's predecessors (X, B, C in the example). X
// trivially dominates itself, so we only have to find if it dominates the
// other predecessors. Since the only way out of X is via NormalDest, X can
// only properly dominate a node if NormalDest dominates that node too.
int IsDuplicateEdge = 0;
for (const_pred_iterator PI = pred_begin(End), E = pred_end(End);
PI != E; ++PI) {
const BasicBlock *BB = *PI;
if (BB == Start) {
// If there are multiple edges between Start and End, by definition they
// can't dominate anything.
if (IsDuplicateEdge++)
return false;
continue;
}
if (!dominates(End, BB))
return false;
}
return true;
}
bool DominatorTree::dominates(const BasicBlockEdge &BBE, const Use &U) const {
Instruction *UserInst = cast<Instruction>(U.getUser());
// A PHI in the end of the edge is dominated by it.
PHINode *PN = dyn_cast<PHINode>(UserInst);
if (PN && PN->getParent() == BBE.getEnd() &&
PN->getIncomingBlock(U) == BBE.getStart())
return true;
// Otherwise use the edge-dominates-block query, which
// handles the crazy critical edge cases properly.
const BasicBlock *UseBB;
if (PN)
UseBB = PN->getIncomingBlock(U);
else
UseBB = UserInst->getParent();
return dominates(BBE, UseBB);
}
bool DominatorTree::dominates(const Instruction *Def, const Use &U) const {
Instruction *UserInst = cast<Instruction>(U.getUser());
const BasicBlock *DefBB = Def->getParent();
// Determine the block in which the use happens. PHI nodes use
// their operands on edges; simulate this by thinking of the use
// happening at the end of the predecessor block.
const BasicBlock *UseBB;
if (PHINode *PN = dyn_cast<PHINode>(UserInst))
UseBB = PN->getIncomingBlock(U);
else
UseBB = UserInst->getParent();
// Any unreachable use is dominated, even if Def == User.
if (!isReachableFromEntry(UseBB))
return true;
// Unreachable definitions don't dominate anything.
if (!isReachableFromEntry(DefBB))
return false;
// Invoke instructions define their return values on the edges to their normal
// successors, so we have to handle them specially.
// Among other things, this means they don't dominate anything in
// their own block, except possibly a phi, so we don't need to
// walk the block in any case.
if (const InvokeInst *II = dyn_cast<InvokeInst>(Def)) {
BasicBlock *NormalDest = II->getNormalDest();
BasicBlockEdge E(DefBB, NormalDest);
return dominates(E, U);
}
// If the def and use are in different blocks, do a simple CFG dominator
// tree query.
if (DefBB != UseBB)
return dominates(DefBB, UseBB);
// Ok, def and use are in the same block. If the def is an invoke, it
// doesn't dominate anything in the block. If it's a PHI, it dominates
// everything in the block.
if (isa<PHINode>(UserInst))
return true;
// Otherwise, just loop through the basic block until we find Def or User.
BasicBlock::const_iterator I = DefBB->begin();
for (; &*I != Def && &*I != UserInst; ++I)
/*empty*/;
return &*I != UserInst;
}
bool DominatorTree::isReachableFromEntry(const Use &U) const {
Instruction *I = dyn_cast<Instruction>(U.getUser());
// ConstantExprs aren't really reachable from the entry block, but they
// don't need to be treated like unreachable code either.
if (!I) return true;
// PHI nodes use their operands on their incoming edges.
if (PHINode *PN = dyn_cast<PHINode>(I))
return isReachableFromEntry(PN->getIncomingBlock(U));
// Everything else uses their operands in their own block.
return isReachableFromEntry(I->getParent());
}
//===----------------------------------------------------------------------===//
// DominatorTreeAnalysis and related pass implementations
//===----------------------------------------------------------------------===//
//
// This implements the DominatorTreeAnalysis which is used with the new pass
// manager. It also implements some methods from utility passes.
//
//===----------------------------------------------------------------------===//
DominatorTree DominatorTreeAnalysis::run(Function &F,
FunctionAnalysisManager &) {
DominatorTree DT;
DT.recalculate(F);
return DT;
}
AnalysisKey DominatorTreeAnalysis::Key;
DominatorTreePrinterPass::DominatorTreePrinterPass(raw_ostream &OS) : OS(OS) {}
PreservedAnalyses DominatorTreePrinterPass::run(Function &F,
FunctionAnalysisManager &AM) {
OS << "DominatorTree for function: " << F.getName() << "\n";
AM.getResult<DominatorTreeAnalysis>(F).print(OS);
return PreservedAnalyses::all();
}
PreservedAnalyses DominatorTreeVerifierPass::run(Function &F,
FunctionAnalysisManager &AM) {
auto &DT = AM.getResult<DominatorTreeAnalysis>(F);
assert(DT.verify());
(void)DT;
return PreservedAnalyses::all();
}
//===----------------------------------------------------------------------===//
// DominatorTreeWrapperPass Implementation
//===----------------------------------------------------------------------===//
//
// The implementation details of the wrapper pass that holds a DominatorTree
// suitable for use with the legacy pass manager.
//
//===----------------------------------------------------------------------===//
char DominatorTreeWrapperPass::ID = 0;
INITIALIZE_PASS(DominatorTreeWrapperPass, "domtree",
"Dominator Tree Construction", true, true)
bool DominatorTreeWrapperPass::runOnFunction(Function &F) {
DT.recalculate(F);
return false;
}
void DominatorTreeWrapperPass::verifyAnalysis() const {
if (VerifyDomInfo)
assert(DT.verify(DominatorTree::VerificationLevel::Full));
else if (ExpensiveChecksEnabled)
assert(DT.verify(DominatorTree::VerificationLevel::Basic));
}
void DominatorTreeWrapperPass::print(raw_ostream &OS, const Module *) const {
DT.print(OS);
}
//===----------------------------------------------------------------------===//
// DeferredDominance Implementation
//===----------------------------------------------------------------------===//
//
// The implementation details of the DeferredDominance class which allows
// one to queue updates to a DominatorTree.
//
//===----------------------------------------------------------------------===//
/// Queues multiple updates and discards duplicates.
void DeferredDominance::applyUpdates(
ArrayRef<DominatorTree::UpdateType> Updates) {
SmallVector<DominatorTree::UpdateType, 8> Seen;
for (auto U : Updates)
// Avoid duplicates to applyUpdate() to save on analysis.
if (std::none_of(Seen.begin(), Seen.end(),
[U](DominatorTree::UpdateType S) { return S == U; })) {
Seen.push_back(U);
applyUpdate(U.getKind(), U.getFrom(), U.getTo());
}
}
/// Helper method for a single edge insertion. It's almost always better
/// to batch updates and call applyUpdates to quickly remove duplicate edges.
/// This is best used when there is only a single insertion needed to update
/// Dominators.
void DeferredDominance::insertEdge(BasicBlock *From, BasicBlock *To) {
applyUpdate(DominatorTree::Insert, From, To);
}
/// Helper method for a single edge deletion. It's almost always better
/// to batch updates and call applyUpdates to quickly remove duplicate edges.
/// This is best used when there is only a single deletion needed to update
/// Dominators.
void DeferredDominance::deleteEdge(BasicBlock *From, BasicBlock *To) {
applyUpdate(DominatorTree::Delete, From, To);
}
/// Delays the deletion of a basic block until a flush() event.
void DeferredDominance::deleteBB(BasicBlock *DelBB) {
assert(DelBB && "Invalid push_back of nullptr DelBB.");
assert(pred_empty(DelBB) && "DelBB has one or more predecessors.");
// DelBB is unreachable and all its instructions are dead.
while (!DelBB->empty()) {
Instruction &I = DelBB->back();
// Replace used instructions with an arbitrary value (undef).
if (!I.use_empty())
I.replaceAllUsesWith(llvm::UndefValue::get(I.getType()));
DelBB->getInstList().pop_back();
}
// Make sure DelBB has a valid terminator instruction. As long as DelBB is a
// Child of Function F it must contain valid IR.
new UnreachableInst(DelBB->getContext(), DelBB);
DeletedBBs.insert(DelBB);
}
/// Returns true if DelBB is awaiting deletion at a flush() event.
bool DeferredDominance::pendingDeletedBB(BasicBlock *DelBB) {
if (DeletedBBs.empty())
return false;
return DeletedBBs.count(DelBB) != 0;
}
/// Returns true if pending DT updates are queued for a flush() event.
bool DeferredDominance::pending() { return !PendUpdates.empty(); }
/// Flushes all pending updates and block deletions. Returns a
/// correct DominatorTree reference to be used by the caller for analysis.
DominatorTree &DeferredDominance::flush() {
// Updates to DT must happen before blocks are deleted below. Otherwise the
// DT traversal will encounter badref blocks and assert.
if (!PendUpdates.empty()) {
DT.applyUpdates(PendUpdates);
PendUpdates.clear();
}
flushDelBB();
return DT;
}
/// Drops all internal state and forces a (slow) recalculation of the
/// DominatorTree based on the current state of the LLVM IR in F. This should
/// only be used in corner cases such as the Entry block of F being deleted.
void DeferredDominance::recalculate(Function &F) {
// flushDelBB must be flushed before the recalculation. The state of the IR
// must be consistent before the DT traversal algorithm determines the
// actual DT.
if (flushDelBB() || !PendUpdates.empty()) {
DT.recalculate(F);
PendUpdates.clear();
}
}
/// Debug method to help view the state of pending updates.
#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
LLVM_DUMP_METHOD void DeferredDominance::dump() const {
raw_ostream &OS = llvm::dbgs();
OS << "PendUpdates:\n";
int I = 0;
for (auto U : PendUpdates) {
OS << " " << I << " : ";
++I;
if (U.getKind() == DominatorTree::Insert)
OS << "Insert, ";
else
OS << "Delete, ";
BasicBlock *From = U.getFrom();
if (From) {
auto S = From->getName();
if (!From->hasName())
S = "(no name)";
OS << S << "(" << From << "), ";
} else {
OS << "(badref), ";
}
BasicBlock *To = U.getTo();
if (To) {
auto S = To->getName();
if (!To->hasName())
S = "(no_name)";
OS << S << "(" << To << ")\n";
} else {
OS << "(badref)\n";
}
}
OS << "DeletedBBs:\n";
I = 0;
for (auto BB : DeletedBBs) {
OS << " " << I << " : ";
++I;
if (BB->hasName())
OS << BB->getName() << "(";
else
OS << "(no_name)(";
OS << BB << ")\n";
}
}
#endif
/// Apply an update (Kind, From, To) to the internal queued updates. The
/// update is only added when determined to be necessary. Checks for
/// self-domination, unnecessary updates, duplicate requests, and balanced
/// pairs of requests are all performed. Returns true if the update is
/// queued and false if it is discarded.
bool DeferredDominance::applyUpdate(DominatorTree::UpdateKind Kind,
BasicBlock *From, BasicBlock *To) {
if (From == To)
return false; // Cannot dominate self; discard update.
// Discard updates by inspecting the current state of successors of From.
// Since applyUpdate() must be called *after* the Terminator of From is
// altered we can determine if the update is unnecessary.
bool HasEdge = std::any_of(succ_begin(From), succ_end(From),
[To](BasicBlock *B) { return B == To; });
if (Kind == DominatorTree::Insert && !HasEdge)
return false; // Unnecessary Insert: edge does not exist in IR.
if (Kind == DominatorTree::Delete && HasEdge)
return false; // Unnecessary Delete: edge still exists in IR.
// Analyze pending updates to determine if the update is unnecessary.
DominatorTree::UpdateType Update = {Kind, From, To};
DominatorTree::UpdateType Invert = {Kind != DominatorTree::Insert
? DominatorTree::Insert
: DominatorTree::Delete,
From, To};
for (auto I = PendUpdates.begin(), E = PendUpdates.end(); I != E; ++I) {
if (Update == *I)
return false; // Discard duplicate updates.
if (Invert == *I) {
// Update and Invert are both valid (equivalent to a no-op). Remove
// Invert from PendUpdates and discard the Update.
PendUpdates.erase(I);
return false;
}
}
PendUpdates.push_back(Update); // Save the valid update.
return true;
}
/// Performs all pending basic block deletions. We have to defer the deletion
/// of these blocks until after the DominatorTree updates are applied. The
/// internal workings of the DominatorTree code expect every update's From
/// and To blocks to exist and to be a member of the same Function.
bool DeferredDominance::flushDelBB() {
if (DeletedBBs.empty())
return false;
for (auto *BB : DeletedBBs)
BB->eraseFromParent();
DeletedBBs.clear();
return true;
}