412 lines
15 KiB
C++
412 lines
15 KiB
C++
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//===- Dominators.cpp - Dominator Calculation -----------------------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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//
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// This file implements simple dominator construction algorithms for finding
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// forward dominators. Postdominators are available in libanalysis, but are not
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// included in libvmcore, because it's not needed. Forward dominators are
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// needed to support the Verifier pass.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/IR/Dominators.h"
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#include "llvm/ADT/DepthFirstIterator.h"
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#include "llvm/ADT/SmallPtrSet.h"
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#include "llvm/Config/llvm-config.h"
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#include "llvm/IR/CFG.h"
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#include "llvm/IR/Constants.h"
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#include "llvm/IR/Instructions.h"
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#include "llvm/IR/PassManager.h"
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#include "llvm/InitializePasses.h"
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#include "llvm/Support/CommandLine.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/Support/GenericDomTreeConstruction.h"
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#include "llvm/Support/raw_ostream.h"
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#include <algorithm>
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using namespace llvm;
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bool llvm::VerifyDomInfo = false;
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static cl::opt<bool, true>
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VerifyDomInfoX("verify-dom-info", cl::location(VerifyDomInfo), cl::Hidden,
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cl::desc("Verify dominator info (time consuming)"));
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#ifdef EXPENSIVE_CHECKS
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static constexpr bool ExpensiveChecksEnabled = true;
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#else
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static constexpr bool ExpensiveChecksEnabled = false;
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#endif
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bool BasicBlockEdge::isSingleEdge() const {
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const Instruction *TI = Start->getTerminator();
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unsigned NumEdgesToEnd = 0;
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for (unsigned int i = 0, n = TI->getNumSuccessors(); i < n; ++i) {
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if (TI->getSuccessor(i) == End)
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++NumEdgesToEnd;
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if (NumEdgesToEnd >= 2)
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return false;
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}
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assert(NumEdgesToEnd == 1);
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return true;
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}
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//===----------------------------------------------------------------------===//
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// DominatorTree Implementation
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//===----------------------------------------------------------------------===//
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//
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// Provide public access to DominatorTree information. Implementation details
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// can be found in Dominators.h, GenericDomTree.h, and
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// GenericDomTreeConstruction.h.
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//
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//===----------------------------------------------------------------------===//
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template class llvm::DomTreeNodeBase<BasicBlock>;
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template class llvm::DominatorTreeBase<BasicBlock, false>; // DomTreeBase
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template class llvm::DominatorTreeBase<BasicBlock, true>; // PostDomTreeBase
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template class llvm::cfg::Update<BasicBlock *>;
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template void llvm::DomTreeBuilder::Calculate<DomTreeBuilder::BBDomTree>(
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DomTreeBuilder::BBDomTree &DT);
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template void
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llvm::DomTreeBuilder::CalculateWithUpdates<DomTreeBuilder::BBDomTree>(
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DomTreeBuilder::BBDomTree &DT, BBUpdates U);
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template void llvm::DomTreeBuilder::Calculate<DomTreeBuilder::BBPostDomTree>(
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DomTreeBuilder::BBPostDomTree &DT);
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// No CalculateWithUpdates<PostDomTree> instantiation, unless a usecase arises.
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template void llvm::DomTreeBuilder::InsertEdge<DomTreeBuilder::BBDomTree>(
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DomTreeBuilder::BBDomTree &DT, BasicBlock *From, BasicBlock *To);
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template void llvm::DomTreeBuilder::InsertEdge<DomTreeBuilder::BBPostDomTree>(
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DomTreeBuilder::BBPostDomTree &DT, BasicBlock *From, BasicBlock *To);
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template void llvm::DomTreeBuilder::DeleteEdge<DomTreeBuilder::BBDomTree>(
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DomTreeBuilder::BBDomTree &DT, BasicBlock *From, BasicBlock *To);
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template void llvm::DomTreeBuilder::DeleteEdge<DomTreeBuilder::BBPostDomTree>(
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DomTreeBuilder::BBPostDomTree &DT, BasicBlock *From, BasicBlock *To);
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template void llvm::DomTreeBuilder::ApplyUpdates<DomTreeBuilder::BBDomTree>(
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DomTreeBuilder::BBDomTree &DT, DomTreeBuilder::BBDomTreeGraphDiff &,
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DomTreeBuilder::BBDomTreeGraphDiff *);
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template void llvm::DomTreeBuilder::ApplyUpdates<DomTreeBuilder::BBPostDomTree>(
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DomTreeBuilder::BBPostDomTree &DT, DomTreeBuilder::BBPostDomTreeGraphDiff &,
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DomTreeBuilder::BBPostDomTreeGraphDiff *);
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template bool llvm::DomTreeBuilder::Verify<DomTreeBuilder::BBDomTree>(
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const DomTreeBuilder::BBDomTree &DT,
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DomTreeBuilder::BBDomTree::VerificationLevel VL);
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template bool llvm::DomTreeBuilder::Verify<DomTreeBuilder::BBPostDomTree>(
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const DomTreeBuilder::BBPostDomTree &DT,
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DomTreeBuilder::BBPostDomTree::VerificationLevel VL);
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bool DominatorTree::invalidate(Function &F, const PreservedAnalyses &PA,
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FunctionAnalysisManager::Invalidator &) {
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// Check whether the analysis, all analyses on functions, or the function's
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// CFG have been preserved.
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auto PAC = PA.getChecker<DominatorTreeAnalysis>();
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return !(PAC.preserved() || PAC.preservedSet<AllAnalysesOn<Function>>() ||
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PAC.preservedSet<CFGAnalyses>());
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}
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// dominates - Return true if Def dominates a use in User. This performs
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// the special checks necessary if Def and User are in the same basic block.
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// Note that Def doesn't dominate a use in Def itself!
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bool DominatorTree::dominates(const Value *DefV,
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const Instruction *User) const {
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const Instruction *Def = dyn_cast<Instruction>(DefV);
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if (!Def) {
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assert((isa<Argument>(DefV) || isa<Constant>(DefV)) &&
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"Should be called with an instruction, argument or constant");
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return true; // Arguments and constants dominate everything.
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}
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const BasicBlock *UseBB = User->getParent();
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const BasicBlock *DefBB = Def->getParent();
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// Any unreachable use is dominated, even if Def == User.
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if (!isReachableFromEntry(UseBB))
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return true;
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// Unreachable definitions don't dominate anything.
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if (!isReachableFromEntry(DefBB))
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return false;
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// An instruction doesn't dominate a use in itself.
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if (Def == User)
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return false;
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// The value defined by an invoke dominates an instruction only if it
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// dominates every instruction in UseBB.
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// A PHI is dominated only if the instruction dominates every possible use in
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// the UseBB.
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if (isa<InvokeInst>(Def) || isa<CallBrInst>(Def) || isa<PHINode>(User))
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return dominates(Def, UseBB);
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if (DefBB != UseBB)
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return dominates(DefBB, UseBB);
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return Def->comesBefore(User);
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}
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// true if Def would dominate a use in any instruction in UseBB.
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// note that dominates(Def, Def->getParent()) is false.
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bool DominatorTree::dominates(const Instruction *Def,
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const BasicBlock *UseBB) const {
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const BasicBlock *DefBB = Def->getParent();
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// Any unreachable use is dominated, even if DefBB == UseBB.
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if (!isReachableFromEntry(UseBB))
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return true;
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// Unreachable definitions don't dominate anything.
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if (!isReachableFromEntry(DefBB))
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return false;
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if (DefBB == UseBB)
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return false;
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// Invoke results are only usable in the normal destination, not in the
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// exceptional destination.
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if (const auto *II = dyn_cast<InvokeInst>(Def)) {
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BasicBlock *NormalDest = II->getNormalDest();
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BasicBlockEdge E(DefBB, NormalDest);
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return dominates(E, UseBB);
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}
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// Callbr results are similarly only usable in the default destination.
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if (const auto *CBI = dyn_cast<CallBrInst>(Def)) {
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BasicBlock *NormalDest = CBI->getDefaultDest();
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BasicBlockEdge E(DefBB, NormalDest);
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return dominates(E, UseBB);
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}
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return dominates(DefBB, UseBB);
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}
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bool DominatorTree::dominates(const BasicBlockEdge &BBE,
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const BasicBlock *UseBB) const {
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// If the BB the edge ends in doesn't dominate the use BB, then the
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// edge also doesn't.
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const BasicBlock *Start = BBE.getStart();
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const BasicBlock *End = BBE.getEnd();
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if (!dominates(End, UseBB))
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return false;
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// Simple case: if the end BB has a single predecessor, the fact that it
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// dominates the use block implies that the edge also does.
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if (End->getSinglePredecessor())
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return true;
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// The normal edge from the invoke is critical. Conceptually, what we would
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// like to do is split it and check if the new block dominates the use.
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// With X being the new block, the graph would look like:
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//
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// DefBB
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// /\ . .
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// / \ . .
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// / \ . .
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// / \ | |
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// A X B C
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// | \ | /
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// . \|/
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// . NormalDest
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// .
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//
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// Given the definition of dominance, NormalDest is dominated by X iff X
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// dominates all of NormalDest's predecessors (X, B, C in the example). X
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// trivially dominates itself, so we only have to find if it dominates the
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// other predecessors. Since the only way out of X is via NormalDest, X can
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// only properly dominate a node if NormalDest dominates that node too.
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int IsDuplicateEdge = 0;
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for (const_pred_iterator PI = pred_begin(End), E = pred_end(End);
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PI != E; ++PI) {
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const BasicBlock *BB = *PI;
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if (BB == Start) {
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// If there are multiple edges between Start and End, by definition they
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// can't dominate anything.
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if (IsDuplicateEdge++)
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return false;
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continue;
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}
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if (!dominates(End, BB))
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return false;
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}
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return true;
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}
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bool DominatorTree::dominates(const BasicBlockEdge &BBE, const Use &U) const {
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Instruction *UserInst = cast<Instruction>(U.getUser());
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// A PHI in the end of the edge is dominated by it.
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PHINode *PN = dyn_cast<PHINode>(UserInst);
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if (PN && PN->getParent() == BBE.getEnd() &&
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PN->getIncomingBlock(U) == BBE.getStart())
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return true;
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// Otherwise use the edge-dominates-block query, which
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// handles the crazy critical edge cases properly.
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const BasicBlock *UseBB;
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if (PN)
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UseBB = PN->getIncomingBlock(U);
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else
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UseBB = UserInst->getParent();
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return dominates(BBE, UseBB);
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}
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bool DominatorTree::dominates(const Value *DefV, const Use &U) const {
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const Instruction *Def = dyn_cast<Instruction>(DefV);
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if (!Def) {
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assert((isa<Argument>(DefV) || isa<Constant>(DefV)) &&
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"Should be called with an instruction, argument or constant");
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return true; // Arguments and constants dominate everything.
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}
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Instruction *UserInst = cast<Instruction>(U.getUser());
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const BasicBlock *DefBB = Def->getParent();
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// Determine the block in which the use happens. PHI nodes use
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// their operands on edges; simulate this by thinking of the use
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// happening at the end of the predecessor block.
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const BasicBlock *UseBB;
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if (PHINode *PN = dyn_cast<PHINode>(UserInst))
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UseBB = PN->getIncomingBlock(U);
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else
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UseBB = UserInst->getParent();
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// Any unreachable use is dominated, even if Def == User.
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if (!isReachableFromEntry(UseBB))
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return true;
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// Unreachable definitions don't dominate anything.
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if (!isReachableFromEntry(DefBB))
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return false;
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// Invoke instructions define their return values on the edges to their normal
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// successors, so we have to handle them specially.
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// Among other things, this means they don't dominate anything in
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// their own block, except possibly a phi, so we don't need to
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// walk the block in any case.
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if (const InvokeInst *II = dyn_cast<InvokeInst>(Def)) {
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BasicBlock *NormalDest = II->getNormalDest();
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BasicBlockEdge E(DefBB, NormalDest);
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return dominates(E, U);
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}
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// Callbr results are similarly only usable in the default destination.
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if (const auto *CBI = dyn_cast<CallBrInst>(Def)) {
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BasicBlock *NormalDest = CBI->getDefaultDest();
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BasicBlockEdge E(DefBB, NormalDest);
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return dominates(E, U);
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}
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// If the def and use are in different blocks, do a simple CFG dominator
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// tree query.
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if (DefBB != UseBB)
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return dominates(DefBB, UseBB);
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// Ok, def and use are in the same block. If the def is an invoke, it
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// doesn't dominate anything in the block. If it's a PHI, it dominates
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// everything in the block.
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if (isa<PHINode>(UserInst))
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return true;
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return Def->comesBefore(UserInst);
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}
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bool DominatorTree::isReachableFromEntry(const Use &U) const {
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Instruction *I = dyn_cast<Instruction>(U.getUser());
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// ConstantExprs aren't really reachable from the entry block, but they
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// don't need to be treated like unreachable code either.
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if (!I) return true;
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// PHI nodes use their operands on their incoming edges.
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if (PHINode *PN = dyn_cast<PHINode>(I))
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return isReachableFromEntry(PN->getIncomingBlock(U));
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// Everything else uses their operands in their own block.
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return isReachableFromEntry(I->getParent());
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}
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// Edge BBE1 dominates edge BBE2 if they match or BBE1 dominates start of BBE2.
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bool DominatorTree::dominates(const BasicBlockEdge &BBE1,
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const BasicBlockEdge &BBE2) const {
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if (BBE1.getStart() == BBE2.getStart() && BBE1.getEnd() == BBE2.getEnd())
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return true;
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return dominates(BBE1, BBE2.getStart());
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}
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//===----------------------------------------------------------------------===//
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// DominatorTreeAnalysis and related pass implementations
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//===----------------------------------------------------------------------===//
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//
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// This implements the DominatorTreeAnalysis which is used with the new pass
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// manager. It also implements some methods from utility passes.
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//
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//===----------------------------------------------------------------------===//
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DominatorTree DominatorTreeAnalysis::run(Function &F,
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FunctionAnalysisManager &) {
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DominatorTree DT;
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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);
|
||
|
|
}
|