#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/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) {}
/// 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) {
+static void ChangeToUnreachable(Instruction *I) {
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);
+ 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(Context.getUndef(BBI->getType()));
+ BBI->replaceAllUsesWith(UndefValue::get(BBI->getType()));
BB->getInstList().erase(BBI++);
}
}
}
static bool MarkAliveBlocks(BasicBlock *BB,
- SmallPtrSet<BasicBlock*, 128> &Reachable,
- LLVMContext &Context) {
+ SmallPtrSet<BasicBlock*, 128> &Reachable) {
SmallVector<BasicBlock*, 128> Worklist;
Worklist.push_back(BB);
// though.
++BBI;
if (!isa<UnreachableInst>(BBI)) {
- ChangeToUnreachable(BBI, Context);
+ ChangeToUnreachable(BBI);
Changed = true;
}
break;
}
}
+ // 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) &&
- cast<PointerType>(Ptr->getType())->getAddressSpace() == 0)) {
- ChangeToUnreachable(SI, Context);
+ SI->getPointerAddressSpace() == 0)) {
+ ChangeToUnreachable(SI);
Changed = true;
break;
}
/// otherwise.
static bool RemoveUnreachableBlocksFromFn(Function &F) {
SmallPtrSet<BasicBlock*, 128> Reachable;
- bool Changed = MarkAliveBlocks(F.begin(), Reachable, F.getContext());
+ bool Changed = MarkAliveBlocks(F.begin(), Reachable);
// If there are unreachable blocks in the CFG...
if (Reachable.size() == F.size())
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.
projects / oota-llvm.git / blobdiff