+
+/// getNoopInput - If V is a noop (i.e., lowers to no machine code), look
+/// through it (and any transitive noop operands to it) and return its input
+/// value. This is used to determine if a tail call can be formed.
+///
+static const Value *getNoopInput(const Value *V, const TargetLowering &TLI) {
+ // If V is not an instruction, it can't be looked through.
+ const Instruction *I = dyn_cast<Instruction>(V);
+ if (I == 0 || !I->hasOneUse() || I->getNumOperands() == 0) return V;
+
+ Value *Op = I->getOperand(0);
+
+ // Look through truly no-op truncates.
+ if (isa<TruncInst>(I) &&
+ TLI.isTruncateFree(I->getOperand(0)->getType(), I->getType()))
+ return getNoopInput(I->getOperand(0), TLI);
+
+ // Look through truly no-op bitcasts.
+ if (isa<BitCastInst>(I)) {
+ // No type change at all.
+ if (Op->getType() == I->getType())
+ return getNoopInput(Op, TLI);
+
+ // Pointer to pointer cast.
+ if (Op->getType()->isPointerTy() && I->getType()->isPointerTy())
+ return getNoopInput(Op, TLI);
+
+ if (isa<VectorType>(Op->getType()) && isa<VectorType>(I->getType()) &&
+ TLI.isTypeLegal(EVT::getEVT(Op->getType())) &&
+ TLI.isTypeLegal(EVT::getEVT(I->getType())))
+ return getNoopInput(Op, TLI);
+ }
+
+ // Look through inttoptr.
+ if (isa<IntToPtrInst>(I) && !isa<VectorType>(I->getType())) {
+ // Make sure this isn't a truncating or extending cast. We could support
+ // this eventually, but don't bother for now.
+ if (TLI.getPointerTy().getSizeInBits() ==
+ cast<IntegerType>(Op->getType())->getBitWidth())
+ return getNoopInput(Op, TLI);
+ }
+
+ // Look through ptrtoint.
+ if (isa<PtrToIntInst>(I) && !isa<VectorType>(I->getType())) {
+ // Make sure this isn't a truncating or extending cast. We could support
+ // this eventually, but don't bother for now.
+ if (TLI.getPointerTy().getSizeInBits() ==
+ cast<IntegerType>(I->getType())->getBitWidth())
+ return getNoopInput(Op, TLI);
+ }
+
+
+ // Otherwise it's not something we can look through.
+ return V;
+}
+
+