#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/Target/TargetData.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() {
/// 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::Create(TrapFn, "", I);
+ }
+ new UnreachableInst(I->getContext(), I);
// All instructions after this are dead.
BasicBlock::iterator BBI = I, BBE = BB->end();
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.
Changed |= ConstantFoldTerminator(BB);
for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE; ++SI)
Worklist.push_back(*SI);
- }
+ } while (!Worklist.empty());
return Changed;
}
return true;
}
+/// 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);
+ RetBlockPHI = PHINode::Create(Ret->getOperand(0)->getType(), "merge",
+ &RetBlock->front());
+
+ for (pred_iterator PI = pred_begin(RetBlock), E = pred_end(RetBlock);
+ PI != E; ++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;
+}
+
/// IterativeSimplifyCFG - Call SimplifyCFG on all the blocks in the function,
/// iterating until no more changes are made.
-static bool IterativeSimplifyCFG(Function &F) {
+static bool IterativeSimplifyCFG(Function &F, const TargetData *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) {
+ const TargetData *TD = getAnalysisIfAvailable<TargetData>();
bool EverChanged = RemoveUnreachableBlocksFromFn(F);
- EverChanged |= IterativeSimplifyCFG(F);
-
+ EverChanged |= MergeEmptyReturnBlocks(F);
+ EverChanged |= IterativeSimplifyCFG(F, TD);
+
// If neither pass changed anything, we're done.
if (!EverChanged) return false;
// RemoveUnreachableBlocksFromFn doesn't do anything.
if (!RemoveUnreachableBlocksFromFn(F))
return true;
-
+
do {
- EverChanged = IterativeSimplifyCFG(F);
+ EverChanged = IterativeSimplifyCFG(F, TD);
EverChanged |= RemoveUnreachableBlocksFromFn(F);
} while (EverChanged);
-
+
return true;
}