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//===- ReduceArguments.cpp - Specialized Delta 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 a function which calls the Generic Delta pass in order
// to reduce uninteresting Arguments from defined functions.
//
//===----------------------------------------------------------------------===//
#include "ReduceBasicBlocks.h"
#include "llvm/ADT/DenseSet.h"
#include "llvm/IR/BasicBlock.h"
#include "llvm/IR/Instruction.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/LLVMContext.h"
#include "llvm/IR/Value.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/raw_ostream.h"
#include <vector>
using namespace llvm;
/// Replaces BB Terminator with one that only contains Chunk BBs
static void replaceBranchTerminator(BasicBlock &BB,
const DenseSet<BasicBlock *> &BBsToKeep) {
auto *Term = BB.getTerminator();
std::vector<BasicBlock *> ChunkSucessors;
for (auto *Succ : successors(&BB))
if (BBsToKeep.count(Succ))
ChunkSucessors.push_back(Succ);
// BB only references Chunk BBs
if (ChunkSucessors.size() == Term->getNumSuccessors())
return;
bool IsBranch = isa<BranchInst>(Term) || isa<InvokeInst>(Term);
Value *Address = nullptr;
if (auto *IndBI = dyn_cast<IndirectBrInst>(Term))
Address = IndBI->getAddress();
Term->replaceAllUsesWith(UndefValue::get(Term->getType()));
Term->eraseFromParent();
if (ChunkSucessors.empty()) {
auto *FnRetTy = BB.getParent()->getReturnType();
ReturnInst::Create(BB.getContext(),
FnRetTy->isVoidTy() ? nullptr : UndefValue::get(FnRetTy),
&BB);
return;
}
if (IsBranch)
BranchInst::Create(ChunkSucessors[0], &BB);
if (Address) {
auto *NewIndBI =
IndirectBrInst::Create(Address, ChunkSucessors.size(), &BB);
for (auto *Dest : ChunkSucessors)
NewIndBI->addDestination(Dest);
}
}
/// Removes uninteresting BBs from switch, if the default case ends up being
/// uninteresting, the switch is replaced with a void return (since it has to be
/// replace with something)
static void
removeUninterestingBBsFromSwitch(SwitchInst &SwInst,
const DenseSet<BasicBlock *> &BBsToKeep) {
if (!BBsToKeep.count(SwInst.getDefaultDest())) {
auto *FnRetTy = SwInst.getParent()->getParent()->getReturnType();
ReturnInst::Create(SwInst.getContext(),
FnRetTy->isVoidTy() ? nullptr : UndefValue::get(FnRetTy),
SwInst.getParent());
SwInst.eraseFromParent();
} else
for (int I = 0, E = SwInst.getNumCases(); I != E; ++I) {
auto Case = SwInst.case_begin() + I;
if (!BBsToKeep.count(Case->getCaseSuccessor())) {
SwInst.removeCase(Case);
--I;
--E;
}
}
}
/// Removes out-of-chunk arguments from functions, and modifies their calls
/// accordingly. It also removes allocations of out-of-chunk arguments.
static void extractBasicBlocksFromModule(Oracle &O, Module &Program) {
DenseSet<BasicBlock *> BBsToKeep;
SmallVector<BasicBlock *> BBsToDelete;
for (auto &F : Program) {
for (auto &BB : F) {
if (O.shouldKeep())
BBsToKeep.insert(&BB);
else {
BBsToDelete.push_back(&BB);
// Remove out-of-chunk BB from successor phi nodes
for (auto *Succ : successors(&BB))
Succ->removePredecessor(&BB);
}
}
}
// Replace terminators that reference out-of-chunk BBs
for (auto &F : Program)
for (auto &BB : F) {
if (auto *SwInst = dyn_cast<SwitchInst>(BB.getTerminator()))
removeUninterestingBBsFromSwitch(*SwInst, BBsToKeep);
else
replaceBranchTerminator(BB, BBsToKeep);
}
// Replace out-of-chunk switch uses
for (auto &BB : BBsToDelete) {
// Instructions might be referenced in other BBs
for (auto &I : *BB)
I.replaceAllUsesWith(UndefValue::get(I.getType()));
if (BB->getParent()->size() == 1) {
// this is the last basic block of the function, thus we must also make
// sure to remove comdat and set linkage to external
auto F = BB->getParent();
F->deleteBody();
F->setComdat(nullptr);
} else {
BB->eraseFromParent();
}
}
}
void llvm::reduceBasicBlocksDeltaPass(TestRunner &Test) {
outs() << "*** Reducing Basic Blocks...\n";
runDeltaPass(Test, extractBasicBlocksFromModule);
}
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