#include "llvm/Transforms/Utils/Local.h"
#include "llvm/Constants.h"
#include "llvm/Instructions.h"
+#include "llvm/IntrinsicInst.h"
#include "llvm/Module.h"
#include "llvm/Attributes.h"
#include "llvm/Support/CFG.h"
-#include "llvm/Support/Compiler.h"
#include "llvm/Pass.h"
+#include "llvm/DataLayout.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/Statistic.h"
STATISTIC(NumSimpl, "Number of blocks simplified");
namespace {
- struct VISIBILITY_HIDDEN CFGSimplifyPass : public FunctionPass {
+ struct CFGSimplifyPass : public FunctionPass {
static char ID; // Pass identification, replacement for typeid
- CFGSimplifyPass() : FunctionPass(&ID) {}
+ CFGSimplifyPass() : FunctionPass(ID) {
+ initializeCFGSimplifyPassPass(*PassRegistry::getPassRegistry());
+ }
virtual bool runOnFunction(Function &F);
};
}
char CFGSimplifyPass::ID = 0;
-static RegisterPass<CFGSimplifyPass> X("simplifycfg", "Simplify the CFG");
+INITIALIZE_PASS(CFGSimplifyPass, "simplifycfg",
+ "Simplify the CFG", false, false)
// Public interface to the CFGSimplification pass
FunctionPass *llvm::createCFGSimplificationPass() {
return new CFGSimplifyPass();
}
-/// ChangeToUnreachable - Insert an unreachable instruction before the specified
+/// 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) {
+static void changeToUnreachable(Instruction *I, bool UseLLVMTrap) {
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);
-
+
+ // Insert a call to llvm.trap right before this. This turns the undefined
+ // behavior into a hard fail instead of falling through into random code.
+ if (UseLLVMTrap) {
+ Function *TrapFn =
+ Intrinsic::getDeclaration(BB->getParent()->getParent(), Intrinsic::trap);
+ CallInst *CallTrap = CallInst::Create(TrapFn, "", I);
+ CallTrap->setDebugLoc(I->getDebugLoc());
+ }
+ new UnreachableInst(I->getContext(), I);
+
// All instructions after this are dead.
BasicBlock::iterator BBI = I, BBE = BB->end();
while (BBI != BBE) {
}
}
-/// 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()+3, II->op_end());
- CallInst *NewCall = CallInst::Create(II->getCalledValue(), Args.begin(),
- Args.end(), "", II);
+/// changeToCall - Convert the specified invoke into a normal call.
+static void changeToCall(InvokeInst *II) {
+ SmallVector<Value*, 8> Args(II->op_begin(), II->op_end() - 3);
+ CallInst *NewCall = CallInst::Create(II->getCalledValue(), Args, "", II);
NewCall->takeName(II);
NewCall->setCallingConv(II->getCallingConv());
NewCall->setAttributes(II->getAttributes());
+ NewCall->setDebugLoc(II->getDebugLoc());
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);
+ II->getUnwindDest()->removePredecessor(II->getParent());
+ II->eraseFromParent();
}
-static bool MarkAliveBlocks(BasicBlock *BB,
+static bool markAliveBlocks(BasicBlock *BB,
SmallPtrSet<BasicBlock*, 128> &Reachable) {
-
+
SmallVector<BasicBlock*, 128> Worklist;
Worklist.push_back(BB);
bool Changed = false;
- while (!Worklist.empty()) {
- BB = Worklist.back();
- Worklist.pop_back();
-
+ do {
+ BB = Worklist.pop_back_val();
+
if (!Reachable.insert(BB))
continue;
// though.
++BBI;
if (!isa<UnreachableInst>(BBI)) {
- ChangeToUnreachable(BBI);
+ // Don't insert a call to llvm.trap right before the unreachable.
+ changeToUnreachable(BBI, false);
Changed = true;
}
break;
}
}
-
- if (StoreInst *SI = dyn_cast<StoreInst>(BBI))
- if (isa<ConstantPointerNull>(SI->getOperand(1)) ||
- isa<UndefValue>(SI->getOperand(1))) {
- ChangeToUnreachable(SI);
+
+ // Store to undef and store to null are undefined and used to signal that
+ // they should be changed to unreachable by passes that can't modify the
+ // CFG.
+ if (StoreInst *SI = dyn_cast<StoreInst>(BBI)) {
+ // Don't touch volatile stores.
+ if (SI->isVolatile()) continue;
+
+ Value *Ptr = SI->getOperand(1);
+
+ if (isa<UndefValue>(Ptr) ||
+ (isa<ConstantPointerNull>(Ptr) &&
+ SI->getPointerAddressSpace() == 0)) {
+ changeToUnreachable(SI, true);
Changed = true;
break;
}
+ }
}
// Turn invokes that call 'nounwind' functions into ordinary calls.
- if (InvokeInst *II = dyn_cast<InvokeInst>(BB->getTerminator()))
- if (II->doesNotThrow()) {
- ChangeToCall(II);
+ if (InvokeInst *II = dyn_cast<InvokeInst>(BB->getTerminator())) {
+ Value *Callee = II->getCalledValue();
+ if (isa<ConstantPointerNull>(Callee) || isa<UndefValue>(Callee)) {
+ changeToUnreachable(II, true);
+ Changed = true;
+ } else if (II->doesNotThrow()) {
+ if (II->use_empty() && II->onlyReadsMemory()) {
+ // jump to the normal destination branch.
+ BranchInst::Create(II->getNormalDest(), II);
+ II->getUnwindDest()->removePredecessor(II->getParent());
+ II->eraseFromParent();
+ } else
+ changeToCall(II);
Changed = true;
}
+ }
- Changed |= ConstantFoldTerminator(BB);
+ Changed |= ConstantFoldTerminator(BB, true);
for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE; ++SI)
Worklist.push_back(*SI);
- }
+ } while (!Worklist.empty());
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
+/// 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) {
+static bool removeUnreachableBlocksFromFn(Function &F) {
SmallPtrSet<BasicBlock*, 128> Reachable;
- bool Changed = MarkAliveBlocks(F.begin(), Reachable);
-
+ bool Changed = markAliveBlocks(F.begin(), Reachable);
+
// 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;
}
-/// IterativeSimplifyCFG - Call SimplifyCFG on all the blocks in the function,
+/// mergeEmptyReturnBlocks - 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;
+
+ BasicBlock *RetBlock = 0;
+
+ // 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 == 0) 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;
+ }
+
+ // If this is the first returning block, remember it and keep going.
+ if (RetBlock == 0) {
+ RetBlock = &BB;
+ continue;
+ }
+
+ // 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;
+ }
+
+ // If the canonical return block has no PHI node, create one now.
+ PHINode *RetBlockPHI = dyn_cast<PHINode>(RetBlock->begin());
+ if (RetBlockPHI == 0) {
+ 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);
+ }
+
+ // 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;
+}
+
+/// iterativelySimplifyCFG - 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 DataLayout *TD) {
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...
+
+ // 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++)) {
+ for (Function::iterator BBIt = F.begin(); BBIt != F.end(); ) {
+ if (SimplifyCFG(BBIt++, TD)) {
LocalChange = true;
++NumSimpl;
}
// simplify the CFG.
//
bool CFGSimplifyPass::runOnFunction(Function &F) {
- bool EverChanged = RemoveUnreachableBlocksFromFn(F);
- EverChanged |= IterativeSimplifyCFG(F);
-
+ const DataLayout *TD = getAnalysisIfAvailable<DataLayout>();
+ bool EverChanged = removeUnreachableBlocksFromFn(F);
+ EverChanged |= mergeEmptyReturnBlocks(F);
+ EverChanged |= iterativelySimplifyCFG(F, TD);
+
// 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,
+ // removeUnreachableBlocksFromFn 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 reruning iterativelySimplifyCFG if the second pass of
+ // removeUnreachableBlocksFromFn doesn't do anything.
+ if (!removeUnreachableBlocksFromFn(F))
return true;
-
+
do {
- EverChanged = IterativeSimplifyCFG(F);
- EverChanged |= RemoveUnreachableBlocksFromFn(F);
+ EverChanged = iterativelySimplifyCFG(F, TD);
+ EverChanged |= removeUnreachableBlocksFromFn(F);
} while (EverChanged);
-
+
return true;
}
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