#include "llvm/Module.h"
#include "llvm/Attributes.h"
#include "llvm/Support/CFG.h"
-#include "llvm/Support/Compiler.h"
#include "llvm/Pass.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/SmallPtrSet.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) {}
for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE; ++SI)
(*SI)->removePredecessor(BB);
- new UnreachableInst(I);
+ new UnreachableInst(I->getContext(), I);
// All instructions after this are dead.
BasicBlock::iterator BBI = I, BBE = BB->end();
Args.end(), "", II);
NewCall->takeName(II);
NewCall->setCallingConv(II->getCallingConv());
- NewCall->setParamAttrs(II->getParamAttrs());
+ NewCall->setAttributes(II->getAttributes());
II->replaceAllUsesWith(NewCall);
// Follow the call by a branch to the normal destination.
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;
}
}
- if (StoreInst *SI = dyn_cast<StoreInst>(BBI))
- if (isa<ConstantPointerNull>(SI->getOperand(1)) ||
- isa<UndefValue>(SI->getOperand(1))) {
+ // 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)) {
+ Value *Ptr = SI->getOperand(1);
+
+ if (isa<UndefValue>(Ptr) ||
+ (isa<ConstantPointerNull>(Ptr) &&
+ SI->getPointerAddressSpace() == 0)) {
ChangeToUnreachable(SI);
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;
+ if (!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->begin())->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) {
//
bool CFGSimplifyPass::runOnFunction(Function &F) {
bool EverChanged = RemoveUnreachableBlocksFromFn(F);
+ EverChanged |= MergeEmptyReturnBlocks(F);
EverChanged |= IterativeSimplifyCFG(F);
// If neither pass changed anything, we're done.