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//===- FlattenCFGPass.cpp - CFG Flatten Pass ----------------------===//
//
// 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 flattening of CFG.
//
//===----------------------------------------------------------------------===//
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/IR/CFG.h"
#include "llvm/IR/ValueHandle.h"
#include "llvm/InitializePasses.h"
#include "llvm/Pass.h"
#include "llvm/Transforms/Scalar.h"
#include "llvm/Transforms/Utils/Local.h"
using namespace llvm;
#define DEBUG_TYPE "flattencfg"
namespace {
struct FlattenCFGPass : public FunctionPass {
static char ID; // Pass identification, replacement for typeid
public:
FlattenCFGPass() : FunctionPass(ID) {
initializeFlattenCFGPassPass(*PassRegistry::getPassRegistry());
}
bool runOnFunction(Function &F) override;
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.addRequired<AAResultsWrapperPass>();
}
private:
AliasAnalysis *AA;
};
}
char FlattenCFGPass::ID = 0;
INITIALIZE_PASS_BEGIN(FlattenCFGPass, "flattencfg", "Flatten the CFG", false,
false)
INITIALIZE_PASS_DEPENDENCY(AAResultsWrapperPass)
INITIALIZE_PASS_END(FlattenCFGPass, "flattencfg", "Flatten the CFG", false,
false)
// Public interface to the FlattenCFG pass
FunctionPass *llvm::createFlattenCFGPass() { return new FlattenCFGPass(); }
/// iterativelyFlattenCFG - Call FlattenCFG on all the blocks in the function,
/// iterating until no more changes are made.
static bool iterativelyFlattenCFG(Function &F, AliasAnalysis *AA) {
bool Changed = false;
bool LocalChange = true;
// Use block handles instead of iterating over function blocks directly
// to avoid using iterators invalidated by erasing blocks.
std::vector<WeakVH> Blocks;
Blocks.reserve(F.size());
for (auto &BB : F)
Blocks.push_back(&BB);
while (LocalChange) {
LocalChange = false;
// Loop over all of the basic blocks and try to flatten them.
for (WeakVH &BlockHandle : Blocks) {
// Skip blocks erased by FlattenCFG.
if (auto *BB = cast_or_null<BasicBlock>(BlockHandle))
if (FlattenCFG(BB, AA))
LocalChange = true;
}
Changed |= LocalChange;
}
return Changed;
}
bool FlattenCFGPass::runOnFunction(Function &F) {
AA = &getAnalysis<AAResultsWrapperPass>().getAAResults();
bool EverChanged = false;
// iterativelyFlattenCFG can make some blocks dead.
while (iterativelyFlattenCFG(F, AA)) {
removeUnreachableBlocks(F);
EverChanged = true;
}
return EverChanged;
}
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