//
//===----------------------------------------------------------------------===//
-#define DEBUG_TYPE "simplifycfg"
-#include "llvm/Transforms/Scalar.h"
-#include "llvm/Transforms/Utils/Local.h"
-#include "llvm/Constants.h"
-#include "llvm/Instructions.h"
-#include "llvm/LLVMContext.h"
-#include "llvm/Module.h"
-#include "llvm/Attributes.h"
-#include "llvm/Support/CFG.h"
-#include "llvm/Pass.h"
-#include "llvm/ADT/SmallVector.h"
+#include "llvm/Transforms/Scalar/SimplifyCFG.h"
#include "llvm/ADT/SmallPtrSet.h"
+#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
+#include "llvm/Analysis/AssumptionCache.h"
+#include "llvm/Analysis/TargetTransformInfo.h"
+#include "llvm/IR/Attributes.h"
+#include "llvm/IR/CFG.h"
+#include "llvm/IR/Constants.h"
+#include "llvm/IR/DataLayout.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/IntrinsicInst.h"
+#include "llvm/IR/Module.h"
+#include "llvm/Pass.h"
+#include "llvm/Support/CommandLine.h"
+#include "llvm/Transforms/Utils/Local.h"
+#include "llvm/Transforms/Scalar.h"
using namespace llvm;
-STATISTIC(NumSimpl, "Number of blocks simplified");
-
-namespace {
- struct CFGSimplifyPass : public FunctionPass {
- static char ID; // Pass identification, replacement for typeid
- CFGSimplifyPass() : FunctionPass(&ID) {}
-
- virtual bool runOnFunction(Function &F);
- };
-}
+#define DEBUG_TYPE "simplifycfg"
-char CFGSimplifyPass::ID = 0;
-static RegisterPass<CFGSimplifyPass> X("simplifycfg", "Simplify the CFG");
+static cl::opt<unsigned>
+UserBonusInstThreshold("bonus-inst-threshold", cl::Hidden, cl::init(1),
+ cl::desc("Control the number of bonus instructions (default = 1)"));
-// Public interface to the CFGSimplification pass
-FunctionPass *llvm::createCFGSimplificationPass() {
- return new CFGSimplifyPass();
-}
+STATISTIC(NumSimpl, "Number of blocks simplified");
-/// ChangeToUnreachable - Insert an unreachable instruction before the specified
-/// instruction, making it and the rest of the code in the block dead.
-static void ChangeToUnreachable(Instruction *I, LLVMContext &Context) {
- BasicBlock *BB = I->getParent();
- // Loop over all of the successors, removing BB's entry from any PHI
- // nodes.
- for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE; ++SI)
- (*SI)->removePredecessor(BB);
-
- new UnreachableInst(I->getContext(), I);
-
- // All instructions after this are dead.
- BasicBlock::iterator BBI = I, BBE = BB->end();
- while (BBI != BBE) {
- if (!BBI->use_empty())
- BBI->replaceAllUsesWith(UndefValue::get(BBI->getType()));
- BB->getInstList().erase(BBI++);
- }
-}
+/// If we have more than one empty (other than phi node) return blocks,
+/// merge them together to promote recursive block merging.
+static bool mergeEmptyReturnBlocks(Function &F) {
+ bool Changed = false;
-/// ChangeToCall - Convert the specified invoke into a normal call.
-static void ChangeToCall(InvokeInst *II) {
- BasicBlock *BB = II->getParent();
- SmallVector<Value*, 8> Args(II->op_begin(), II->op_end() - 3);
- CallInst *NewCall = CallInst::Create(II->getCalledValue(), Args.begin(),
- Args.end(), "", II);
- NewCall->takeName(II);
- NewCall->setCallingConv(II->getCallingConv());
- NewCall->setAttributes(II->getAttributes());
- II->replaceAllUsesWith(NewCall);
-
- // Follow the call by a branch to the normal destination.
- BranchInst::Create(II->getNormalDest(), II);
-
- // Update PHI nodes in the unwind destination
- II->getUnwindDest()->removePredecessor(BB);
- BB->getInstList().erase(II);
-}
+ BasicBlock *RetBlock = nullptr;
+
+ // Scan all the blocks in the function, looking for empty return blocks.
+ for (Function::iterator BBI = F.begin(), E = F.end(); BBI != E; ) {
+ BasicBlock &BB = *BBI++;
+
+ // Only look at return blocks.
+ ReturnInst *Ret = dyn_cast<ReturnInst>(BB.getTerminator());
+ if (!Ret) continue;
+
+ // Only look at the block if it is empty or the only other thing in it is a
+ // single PHI node that is the operand to the return.
+ if (Ret != &BB.front()) {
+ // Check for something else in the block.
+ BasicBlock::iterator I = Ret;
+ --I;
+ // Skip over debug info.
+ while (isa<DbgInfoIntrinsic>(I) && I != BB.begin())
+ --I;
+ if (!isa<DbgInfoIntrinsic>(I) &&
+ (!isa<PHINode>(I) || I != BB.begin() ||
+ Ret->getNumOperands() == 0 ||
+ Ret->getOperand(0) != I))
+ continue;
+ }
-static bool MarkAliveBlocks(BasicBlock *BB,
- SmallPtrSet<BasicBlock*, 128> &Reachable,
- LLVMContext &Context) {
-
- SmallVector<BasicBlock*, 128> Worklist;
- Worklist.push_back(BB);
- bool Changed = false;
- while (!Worklist.empty()) {
- BB = Worklist.back();
- Worklist.pop_back();
-
- if (!Reachable.insert(BB))
+ // If this is the first returning block, remember it and keep going.
+ if (!RetBlock) {
+ RetBlock = &BB;
continue;
+ }
- // Do a quick scan of the basic block, turning any obviously unreachable
- // instructions into LLVM unreachable insts. The instruction combining pass
- // canonicalizes unreachable insts into stores to null or undef.
- for (BasicBlock::iterator BBI = BB->begin(), E = BB->end(); BBI != E;++BBI){
- if (CallInst *CI = dyn_cast<CallInst>(BBI)) {
- if (CI->doesNotReturn()) {
- // If we found a call to a no-return function, insert an unreachable
- // instruction after it. Make sure there isn't *already* one there
- // though.
- ++BBI;
- if (!isa<UnreachableInst>(BBI)) {
- ChangeToUnreachable(BBI, Context);
- Changed = true;
- }
- break;
- }
- }
-
- if (StoreInst *SI = dyn_cast<StoreInst>(BBI)) {
- Value *Ptr = SI->getOperand(1);
-
- if (isa<UndefValue>(Ptr) ||
- (isa<ConstantPointerNull>(Ptr) &&
- SI->getPointerAddressSpace() == 0)) {
- ChangeToUnreachable(SI, Context);
- Changed = true;
- break;
- }
- }
+ // Otherwise, we found a duplicate return block. Merge the two.
+ Changed = true;
+
+ // Case when there is no input to the return or when the returned values
+ // agree is trivial. Note that they can't agree if there are phis in the
+ // blocks.
+ if (Ret->getNumOperands() == 0 ||
+ Ret->getOperand(0) ==
+ cast<ReturnInst>(RetBlock->getTerminator())->getOperand(0)) {
+ BB.replaceAllUsesWith(RetBlock);
+ BB.eraseFromParent();
+ continue;
}
- // Turn invokes that call 'nounwind' functions into ordinary calls.
- if (InvokeInst *II = dyn_cast<InvokeInst>(BB->getTerminator()))
- if (II->doesNotThrow()) {
- ChangeToCall(II);
- Changed = true;
- }
+ // If the canonical return block has no PHI node, create one now.
+ PHINode *RetBlockPHI = dyn_cast<PHINode>(RetBlock->begin());
+ if (!RetBlockPHI) {
+ Value *InVal = cast<ReturnInst>(RetBlock->getTerminator())->getOperand(0);
+ pred_iterator PB = pred_begin(RetBlock), PE = pred_end(RetBlock);
+ RetBlockPHI = PHINode::Create(Ret->getOperand(0)->getType(),
+ std::distance(PB, PE), "merge",
+ &RetBlock->front());
+
+ for (pred_iterator PI = PB; PI != PE; ++PI)
+ RetBlockPHI->addIncoming(InVal, *PI);
+ RetBlock->getTerminator()->setOperand(0, RetBlockPHI);
+ }
- Changed |= ConstantFoldTerminator(BB);
- for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE; ++SI)
- Worklist.push_back(*SI);
+ // Turn BB into a block that just unconditionally branches to the return
+ // block. This handles the case when the two return blocks have a common
+ // predecessor but that return different things.
+ RetBlockPHI->addIncoming(Ret->getOperand(0), &BB);
+ BB.getTerminator()->eraseFromParent();
+ BranchInst::Create(RetBlock, &BB);
}
- return Changed;
-}
-/// RemoveUnreachableBlocksFromFn - Remove blocks that are not reachable, even
-/// if they are in a dead cycle. Return true if a change was made, false
-/// otherwise.
-static bool RemoveUnreachableBlocksFromFn(Function &F) {
- SmallPtrSet<BasicBlock*, 128> Reachable;
- bool Changed = MarkAliveBlocks(F.begin(), Reachable, F.getContext());
-
- // If there are unreachable blocks in the CFG...
- if (Reachable.size() == F.size())
- return Changed;
-
- assert(Reachable.size() < F.size());
- NumSimpl += F.size()-Reachable.size();
-
- // Loop over all of the basic blocks that are not reachable, dropping all of
- // their internal references...
- for (Function::iterator BB = ++F.begin(), E = F.end(); BB != E; ++BB) {
- if (Reachable.count(BB))
- continue;
-
- for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE; ++SI)
- if (Reachable.count(*SI))
- (*SI)->removePredecessor(BB);
- BB->dropAllReferences();
- }
-
- for (Function::iterator I = ++F.begin(); I != F.end();)
- if (!Reachable.count(I))
- I = F.getBasicBlockList().erase(I);
- else
- ++I;
-
- return true;
+ return Changed;
}
-/// IterativeSimplifyCFG - Call SimplifyCFG on all the blocks in the function,
+/// Call SimplifyCFG on all the blocks in the function,
/// iterating until no more changes are made.
-static bool IterativeSimplifyCFG(Function &F) {
+static bool iterativelySimplifyCFG(Function &F, const TargetTransformInfo &TTI,
+ AssumptionCache *AC,
+ unsigned BonusInstThreshold) {
bool Changed = false;
bool LocalChange = true;
while (LocalChange) {
LocalChange = false;
-
- // Loop over all of the basic blocks (except the first one) and remove them
- // if they are unneeded...
- //
- for (Function::iterator BBIt = ++F.begin(); BBIt != F.end(); ) {
- if (SimplifyCFG(BBIt++)) {
+
+ // Loop over all of the basic blocks and remove them if they are unneeded.
+ for (Function::iterator BBIt = F.begin(); BBIt != F.end(); ) {
+ if (SimplifyCFG(BBIt++, TTI, BonusInstThreshold, AC)) {
LocalChange = true;
++NumSimpl;
}
return Changed;
}
-// It is possible that we may require multiple passes over the code to fully
-// simplify the CFG.
-//
-bool CFGSimplifyPass::runOnFunction(Function &F) {
- bool EverChanged = RemoveUnreachableBlocksFromFn(F);
- EverChanged |= IterativeSimplifyCFG(F);
-
+static bool simplifyFunctionCFG(Function &F, const TargetTransformInfo &TTI,
+ AssumptionCache *AC, int BonusInstThreshold) {
+ bool EverChanged = removeUnreachableBlocks(F);
+ EverChanged |= mergeEmptyReturnBlocks(F);
+ EverChanged |= iterativelySimplifyCFG(F, TTI, AC, BonusInstThreshold);
+
// If neither pass changed anything, we're done.
if (!EverChanged) return false;
- // IterativeSimplifyCFG can (rarely) make some loops dead. If this happens,
- // RemoveUnreachableBlocksFromFn is needed to nuke them, which means we should
+ // iterativelySimplifyCFG can (rarely) make some loops dead. If this happens,
+ // removeUnreachableBlocks is needed to nuke them, which means we should
// iterate between the two optimizations. We structure the code like this to
- // avoid reruning IterativeSimplifyCFG if the second pass of
- // RemoveUnreachableBlocksFromFn doesn't do anything.
- if (!RemoveUnreachableBlocksFromFn(F))
+ // avoid rerunning iterativelySimplifyCFG if the second pass of
+ // removeUnreachableBlocks doesn't do anything.
+ if (!removeUnreachableBlocks(F))
return true;
-
+
do {
- EverChanged = IterativeSimplifyCFG(F);
- EverChanged |= RemoveUnreachableBlocksFromFn(F);
+ EverChanged = iterativelySimplifyCFG(F, TTI, AC, BonusInstThreshold);
+ EverChanged |= removeUnreachableBlocks(F);
} while (EverChanged);
-
+
return true;
}
+
+SimplifyCFGPass::SimplifyCFGPass()
+ : BonusInstThreshold(UserBonusInstThreshold) {}
+
+SimplifyCFGPass::SimplifyCFGPass(int BonusInstThreshold)
+ : BonusInstThreshold(BonusInstThreshold) {}
+
+PreservedAnalyses SimplifyCFGPass::run(Function &F,
+ AnalysisManager<Function> *AM) {
+ auto &TTI = AM->getResult<TargetIRAnalysis>(F);
+ auto &AC = AM->getResult<AssumptionAnalysis>(F);
+
+ if (!simplifyFunctionCFG(F, TTI, &AC, BonusInstThreshold))
+ return PreservedAnalyses::none();
+
+ return PreservedAnalyses::all();
+}
+
+namespace {
+struct CFGSimplifyPass : public FunctionPass {
+ static char ID; // Pass identification, replacement for typeid
+ unsigned BonusInstThreshold;
+ std::function<bool(const Function &)> PredicateFtor;
+
+ CFGSimplifyPass(int T = -1,
+ std::function<bool(const Function &)> Ftor = nullptr)
+ : FunctionPass(ID), PredicateFtor(Ftor) {
+ BonusInstThreshold = (T == -1) ? UserBonusInstThreshold : unsigned(T);
+ initializeCFGSimplifyPassPass(*PassRegistry::getPassRegistry());
+ }
+ bool runOnFunction(Function &F) override {
+ if (PredicateFtor && !PredicateFtor(F))
+ return false;
+
+ if (skipOptnoneFunction(F))
+ return false;
+
+ AssumptionCache *AC =
+ &getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
+ const TargetTransformInfo &TTI =
+ getAnalysis<TargetTransformInfoWrapperPass>().getTTI(F);
+ return simplifyFunctionCFG(F, TTI, AC, BonusInstThreshold);
+ }
+
+ void getAnalysisUsage(AnalysisUsage &AU) const override {
+ AU.addRequired<AssumptionCacheTracker>();
+ AU.addRequired<TargetTransformInfoWrapperPass>();
+ }
+};
+}
+
+char CFGSimplifyPass::ID = 0;
+INITIALIZE_PASS_BEGIN(CFGSimplifyPass, "simplifycfg", "Simplify the CFG", false,
+ false)
+INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass)
+INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
+INITIALIZE_PASS_END(CFGSimplifyPass, "simplifycfg", "Simplify the CFG", false,
+ false)
+
+// Public interface to the CFGSimplification pass
+FunctionPass *
+llvm::createCFGSimplificationPass(int Threshold,
+ std::function<bool(const Function &)> Ftor) {
+ return new CFGSimplifyPass(Threshold, Ftor);
+}
+
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