| //===- Dominators.cpp - Dominator Calculation -----------------------------===// |
| // |
| // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. |
| // See https://llvm.org/LICENSE.txt for license information. |
| // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception |
| // |
| //===----------------------------------------------------------------------===// |
| // |
| // 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/InitializePasses.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 Instruction *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 class llvm::cfg::Update<BasicBlock *>; |
| |
| template void llvm::DomTreeBuilder::Calculate<DomTreeBuilder::BBDomTree>( |
| DomTreeBuilder::BBDomTree &DT); |
| template void |
| llvm::DomTreeBuilder::CalculateWithUpdates<DomTreeBuilder::BBDomTree>( |
| DomTreeBuilder::BBDomTree &DT, BBUpdates U); |
| |
| template void llvm::DomTreeBuilder::Calculate<DomTreeBuilder::BBPostDomTree>( |
| DomTreeBuilder::BBPostDomTree &DT); |
| // No CalculateWithUpdates<PostDomTree> instantiation, unless a usecase arises. |
| |
| 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::BBDomTreeGraphDiff &, |
| DomTreeBuilder::BBDomTreeGraphDiff *); |
| template void llvm::DomTreeBuilder::ApplyUpdates<DomTreeBuilder::BBPostDomTree>( |
| DomTreeBuilder::BBPostDomTree &DT, DomTreeBuilder::BBPostDomTreeGraphDiff &, |
| DomTreeBuilder::BBPostDomTreeGraphDiff *); |
| |
| 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>()); |
| } |
| |
| bool DominatorTree::dominates(const BasicBlock *BB, const Use &U) const { |
| Instruction *UserInst = cast<Instruction>(U.getUser()); |
| if (auto *PN = dyn_cast<PHINode>(UserInst)) |
| // A phi use using a value from a block is dominated by the end of that |
| // block. Note that the phi's parent block may not be. |
| return dominates(BB, PN->getIncomingBlock(U)); |
| else |
| return properlyDominates(BB, UserInst->getParent()); |
| } |
| |
| // 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 Value *DefV, |
| const Instruction *User) const { |
| const Instruction *Def = dyn_cast<Instruction>(DefV); |
| if (!Def) { |
| assert((isa<Argument>(DefV) || isa<Constant>(DefV)) && |
| "Should be called with an instruction, argument or constant"); |
| return true; // Arguments and constants dominate everything. |
| } |
| |
| 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<CallBrInst>(Def) || isa<PHINode>(User)) |
| return dominates(Def, UseBB); |
| |
| if (DefBB != UseBB) |
| return dominates(DefBB, UseBB); |
| |
| return Def->comesBefore(User); |
| } |
| |
| // 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); |
| } |
| |
| // Callbr results are similarly only usable in the default destination. |
| if (const auto *CBI = dyn_cast<CallBrInst>(Def)) { |
| BasicBlock *NormalDest = CBI->getDefaultDest(); |
| 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 BasicBlock *BB : predecessors(End)) { |
| 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 Value *DefV, const Use &U) const { |
| const Instruction *Def = dyn_cast<Instruction>(DefV); |
| if (!Def) { |
| assert((isa<Argument>(DefV) || isa<Constant>(DefV)) && |
| "Should be called with an instruction, argument or constant"); |
| return true; // Arguments and constants dominate everything. |
| } |
| |
| 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); |
| } |
| |
| // Callbr results are similarly only usable in the default destination. |
| if (const auto *CBI = dyn_cast<CallBrInst>(Def)) { |
| BasicBlock *NormalDest = CBI->getDefaultDest(); |
| 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; |
| |
| return Def->comesBefore(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()); |
| } |
| |
| // Edge BBE1 dominates edge BBE2 if they match or BBE1 dominates start of BBE2. |
| bool DominatorTree::dominates(const BasicBlockEdge &BBE1, |
| const BasicBlockEdge &BBE2) const { |
| if (BBE1.getStart() == BBE2.getStart() && BBE1.getEnd() == BBE2.getEnd()) |
| return true; |
| return dominates(BBE1, BBE2.getStart()); |
| } |
| |
| //===----------------------------------------------------------------------===// |
| // 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; |
| |
| DominatorTreeWrapperPass::DominatorTreeWrapperPass() : FunctionPass(ID) { |
| initializeDominatorTreeWrapperPassPass(*PassRegistry::getPassRegistry()); |
| } |
| |
| 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); |
| } |