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a9cd579599
Summary: FlattenCFG may erase unnecessary blocks, which also invalidates iterators to those erased blocks. Before this patch, `iterativelyFlattenCFG` could try to increment a BB iterator after that BB has been removed and crash. This patch makes FlattenCFGPass use `WeakVH` to skip over erased blocks. Reviewers: dblaikie, tstellar, davide, sanjoy, asbirlea, grosser Reviewed By: asbirlea Subscribers: hiraditya, llvm-commits Tags: #llvm Differential Revision: https://reviews.llvm.org/D67672 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@372347 91177308-0d34-0410-b5e6-96231b3b80d8
90 lines
2.7 KiB
C++
90 lines
2.7 KiB
C++
//===- FlattenCFGPass.cpp - CFG Flatten Pass ----------------------===//
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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 flattening of CFG.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Analysis/AliasAnalysis.h"
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#include "llvm/IR/CFG.h"
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#include "llvm/IR/ValueHandle.h"
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#include "llvm/Pass.h"
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#include "llvm/Transforms/Scalar.h"
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#include "llvm/Transforms/Utils/Local.h"
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using namespace llvm;
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#define DEBUG_TYPE "flattencfg"
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namespace {
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struct FlattenCFGPass : public FunctionPass {
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static char ID; // Pass identification, replacement for typeid
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public:
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FlattenCFGPass() : FunctionPass(ID) {
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initializeFlattenCFGPassPass(*PassRegistry::getPassRegistry());
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}
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bool runOnFunction(Function &F) override;
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void getAnalysisUsage(AnalysisUsage &AU) const override {
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AU.addRequired<AAResultsWrapperPass>();
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}
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private:
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AliasAnalysis *AA;
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};
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}
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char FlattenCFGPass::ID = 0;
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INITIALIZE_PASS_BEGIN(FlattenCFGPass, "flattencfg", "Flatten the CFG", false,
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false)
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INITIALIZE_PASS_DEPENDENCY(AAResultsWrapperPass)
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INITIALIZE_PASS_END(FlattenCFGPass, "flattencfg", "Flatten the CFG", false,
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false)
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// Public interface to the FlattenCFG pass
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FunctionPass *llvm::createFlattenCFGPass() { return new FlattenCFGPass(); }
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/// iterativelyFlattenCFG - Call FlattenCFG on all the blocks in the function,
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/// iterating until no more changes are made.
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static bool iterativelyFlattenCFG(Function &F, AliasAnalysis *AA) {
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bool Changed = false;
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bool LocalChange = true;
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// Use block handles instead of iterating over function blocks directly
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// to avoid using iterators invalidated by erasing blocks.
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std::vector<WeakVH> Blocks;
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Blocks.reserve(F.size());
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for (auto &BB : F)
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Blocks.push_back(&BB);
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while (LocalChange) {
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LocalChange = false;
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// Loop over all of the basic blocks and try to flatten them.
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for (WeakVH &BlockHandle : Blocks) {
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// Skip blocks erased by FlattenCFG.
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if (auto *BB = cast_or_null<BasicBlock>(BlockHandle))
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if (FlattenCFG(BB, AA))
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LocalChange = true;
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}
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Changed |= LocalChange;
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}
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return Changed;
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}
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bool FlattenCFGPass::runOnFunction(Function &F) {
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AA = &getAnalysis<AAResultsWrapperPass>().getAAResults();
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bool EverChanged = false;
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// iterativelyFlattenCFG can make some blocks dead.
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while (iterativelyFlattenCFG(F, AA)) {
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removeUnreachableBlocks(F);
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EverChanged = true;
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}
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return EverChanged;
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}
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