/// 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, LLVMContext *Context) {
BasicBlock *BB = I->getParent();
// Loop over all of the successors, removing BB's entry from any PHI
// nodes.
static bool MarkAliveBlocks(BasicBlock *BB,
SmallPtrSet<BasicBlock*, 128> &Reachable,
- LLVMContext* Context) {
+ LLVMContext *Context) {
SmallVector<BasicBlock*, 128> Worklist;
Worklist.push_back(BB);
if (!Reachable.insert(BB))
continue;
+ bool AsmFound = false;
+ StoreInst *UndefStore = 0;
// 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.
}
break;
}
+ if (isa<InlineAsm>(CI->getOperand(0)))
+ AsmFound = true;
}
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);
- Changed = true;
- break;
- }
+
+ if ((isa<UndefValue>(Ptr) ||
+ (isa<ConstantPointerNull>(Ptr) &&
+ cast<PointerType>(Ptr->getType())->getAddressSpace() == 0)) &&
+ !UndefStore)
+ UndefStore = SI;
}
}
+ // We can't delete asm's just because their inputs are undefined;
+ // xor R, R is a common idiom for zeroing a register, for example.
+ // Assume user knows what he is doing.
+ if (UndefStore && !AsmFound) {
+ ChangeToUnreachable(UndefStore, Context);
+ Changed = true;
+ }
// Turn invokes that call 'nounwind' functions into ordinary calls.
if (InvokeInst *II = dyn_cast<InvokeInst>(BB->getTerminator()))