Turn casts into getelementptr's when possible. This enables SROA to be more
aggressive in some cases where LLVMGCC 4 is inserting casts for no reason.
This implements InstCombine/cast.ll:test27/28.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@27620 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Transforms/Scalar/InstructionCombining.cpp b/lib/Transforms/Scalar/InstructionCombining.cpp
index f79a48e..f9b01c7 100644
--- a/lib/Transforms/Scalar/InstructionCombining.cpp
+++ b/lib/Transforms/Scalar/InstructionCombining.cpp
@@ -4813,7 +4813,30 @@
if (isa<PHINode>(Src))
if (Instruction *NV = FoldOpIntoPhi(CI))
return NV;
+
+ // If the source and destination are pointers, and this cast is equivalent to
+ // a getelementptr X, 0, 0, 0... turn it into the appropriate getelementptr.
+ // This can enhance SROA and other transforms that want type-safe pointers.
+ if (const PointerType *DstPTy = dyn_cast<PointerType>(CI.getType()))
+ if (const PointerType *SrcPTy = dyn_cast<PointerType>(Src->getType())) {
+ const Type *DstTy = DstPTy->getElementType();
+ const Type *SrcTy = SrcPTy->getElementType();
+
+ Constant *ZeroUInt = Constant::getNullValue(Type::UIntTy);
+ unsigned NumZeros = 0;
+ while (SrcTy != DstTy &&
+ isa<CompositeType>(SrcTy) && !isa<PointerType>(SrcTy)) {
+ SrcTy = cast<CompositeType>(SrcTy)->getTypeAtIndex(ZeroUInt);
+ ++NumZeros;
+ }
+ // If we found a path from the src to dest, create the getelementptr now.
+ if (SrcTy == DstTy) {
+ std::vector<Value*> Idxs(NumZeros+1, ZeroUInt);
+ return new GetElementPtrInst(Src, Idxs);
+ }
+ }
+
// If the source value is an instruction with only this use, we can attempt to
// propagate the cast into the instruction. Also, only handle integral types
// for now.