forked from OSchip/llvm-project
565 lines
21 KiB
C++
565 lines
21 KiB
C++
//===- Dominators.cpp - Dominator Calculation -----------------------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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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/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 TerminatorInst *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 struct llvm::DomTreeBuilder::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 llvm::DomTreeBuilder::Calculate<DomTreeBuilder::BBPostDomTree>(
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DomTreeBuilder::BBPostDomTree &DT);
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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::BBUpdates);
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template void llvm::DomTreeBuilder::ApplyUpdates<DomTreeBuilder::BBPostDomTree>(
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DomTreeBuilder::BBPostDomTree &DT, DomTreeBuilder::BBUpdates);
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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 Instruction *Def,
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const Instruction *User) const {
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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<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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// Loop through the basic block until we find Def or User.
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BasicBlock::const_iterator I = DefBB->begin();
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for (; &*I != Def && &*I != User; ++I)
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/*empty*/;
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return &*I == Def;
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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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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 Instruction *Def, const Use &U) const {
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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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// 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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// Otherwise, just loop through the basic block until we find Def or User.
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BasicBlock::const_iterator I = DefBB->begin();
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for (; &*I != Def && &*I != UserInst; ++I)
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/*empty*/;
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return &*I != 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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//===----------------------------------------------------------------------===//
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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);
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return DT;
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}
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AnalysisKey DominatorTreeAnalysis::Key;
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DominatorTreePrinterPass::DominatorTreePrinterPass(raw_ostream &OS) : OS(OS) {}
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PreservedAnalyses DominatorTreePrinterPass::run(Function &F,
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FunctionAnalysisManager &AM) {
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OS << "DominatorTree for function: " << F.getName() << "\n";
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AM.getResult<DominatorTreeAnalysis>(F).print(OS);
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return PreservedAnalyses::all();
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}
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PreservedAnalyses DominatorTreeVerifierPass::run(Function &F,
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FunctionAnalysisManager &AM) {
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auto &DT = AM.getResult<DominatorTreeAnalysis>(F);
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assert(DT.verify());
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(void)DT;
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return PreservedAnalyses::all();
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}
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//===----------------------------------------------------------------------===//
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// DominatorTreeWrapperPass Implementation
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//===----------------------------------------------------------------------===//
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//
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// The implementation details of the wrapper pass that holds a DominatorTree
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// suitable for use with the legacy pass manager.
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//
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//===----------------------------------------------------------------------===//
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char DominatorTreeWrapperPass::ID = 0;
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INITIALIZE_PASS(DominatorTreeWrapperPass, "domtree",
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"Dominator Tree Construction", true, true)
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bool DominatorTreeWrapperPass::runOnFunction(Function &F) {
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DT.recalculate(F);
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return false;
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}
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void DominatorTreeWrapperPass::verifyAnalysis() const {
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if (VerifyDomInfo)
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assert(DT.verify(DominatorTree::VerificationLevel::Full));
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else if (ExpensiveChecksEnabled)
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assert(DT.verify(DominatorTree::VerificationLevel::Basic));
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}
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void DominatorTreeWrapperPass::print(raw_ostream &OS, const Module *) const {
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DT.print(OS);
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}
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//===----------------------------------------------------------------------===//
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// DeferredDominance Implementation
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//===----------------------------------------------------------------------===//
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//
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// The implementation details of the DeferredDominance class which allows
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// one to queue updates to a DominatorTree.
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//
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//===----------------------------------------------------------------------===//
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/// \brief Queues multiple updates and discards duplicates.
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void DeferredDominance::applyUpdates(
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ArrayRef<DominatorTree::UpdateType> Updates) {
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SmallVector<DominatorTree::UpdateType, 8> Seen;
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for (auto U : Updates)
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// Avoid duplicates to applyUpdate() to save on analysis.
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if (std::none_of(Seen.begin(), Seen.end(),
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[U](DominatorTree::UpdateType S) { return S == U; })) {
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Seen.push_back(U);
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applyUpdate(U.getKind(), U.getFrom(), U.getTo());
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}
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}
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/// \brief Helper method for a single edge insertion. It's almost always better
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/// to batch updates and call applyUpdates to quickly remove duplicate edges.
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/// This is best used when there is only a single insertion needed to update
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/// Dominators.
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void DeferredDominance::insertEdge(BasicBlock *From, BasicBlock *To) {
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applyUpdate(DominatorTree::Insert, From, To);
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}
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/// \brief Helper method for a single edge deletion. It's almost always better
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/// to batch updates and call applyUpdates to quickly remove duplicate edges.
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/// This is best used when there is only a single deletion needed to update
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/// Dominators.
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void DeferredDominance::deleteEdge(BasicBlock *From, BasicBlock *To) {
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applyUpdate(DominatorTree::Delete, From, To);
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}
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/// \brief Delays the deletion of a basic block until a flush() event.
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void DeferredDominance::deleteBB(BasicBlock *DelBB) {
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assert(DelBB && "Invalid push_back of nullptr DelBB.");
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assert(pred_empty(DelBB) && "DelBB has one or more predecessors.");
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// DelBB is unreachable and all its instructions are dead.
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while (!DelBB->empty()) {
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Instruction &I = DelBB->back();
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// Replace used instructions with an arbitrary value (undef).
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if (!I.use_empty())
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I.replaceAllUsesWith(llvm::UndefValue::get(I.getType()));
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DelBB->getInstList().pop_back();
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}
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// Make sure DelBB has a valid terminator instruction. As long as DelBB is a
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// Child of Function F it must contain valid IR.
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new UnreachableInst(DelBB->getContext(), DelBB);
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DeletedBBs.insert(DelBB);
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}
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/// \brief Returns true if DelBB is awaiting deletion at a flush() event.
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bool DeferredDominance::pendingDeletedBB(BasicBlock *DelBB) {
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if (DeletedBBs.empty())
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return false;
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return DeletedBBs.count(DelBB) != 0;
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}
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/// \brief Returns true if pending DT updates are queued for a flush() event.
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bool DeferredDominance::pending() { return !PendUpdates.empty(); }
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/// \brief Flushes all pending updates and block deletions. Returns a
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/// correct DominatorTree reference to be used by the caller for analysis.
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DominatorTree &DeferredDominance::flush() {
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// Updates to DT must happen before blocks are deleted below. Otherwise the
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// DT traversal will encounter badref blocks and assert.
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if (!PendUpdates.empty()) {
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DT.applyUpdates(PendUpdates);
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PendUpdates.clear();
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}
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flushDelBB();
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return DT;
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}
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/// \brief Drops all internal state and forces a (slow) recalculation of the
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/// DominatorTree based on the current state of the LLVM IR in F. This should
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/// only be used in corner cases such as the Entry block of F being deleted.
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void DeferredDominance::recalculate(Function &F) {
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// flushDelBB must be flushed before the recalculation. The state of the IR
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// must be consistent before the DT traversal algorithm determines the
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// actual DT.
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if (flushDelBB() || !PendUpdates.empty()) {
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DT.recalculate(F);
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PendUpdates.clear();
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}
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}
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/// \brief Debug method to help view the state of pending updates.
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#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
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LLVM_DUMP_METHOD void DeferredDominance::dump() const {
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raw_ostream &OS = llvm::dbgs();
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OS << "PendUpdates:\n";
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int I = 0;
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for (auto U : PendUpdates) {
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OS << " " << I << " : ";
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++I;
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if (U.getKind() == DominatorTree::Insert)
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OS << "Insert, ";
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else
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OS << "Delete, ";
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BasicBlock *From = U.getFrom();
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if (From) {
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auto S = From->getName();
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if (!From->hasName())
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S = "(no name)";
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OS << S << "(" << From << "), ";
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} else {
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OS << "(badref), ";
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}
|
|
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;
|
|
}
|