Fixes following the CR by Chris and Duncan:
Optimize chained bitcasts of the form A->B->A.
Undo r138722 and change isEliminableCastPair to allow this case.
llvm-svn: 138756
diff --git a/llvm/lib/VMCore/Instructions.cpp b/llvm/lib/VMCore/Instructions.cpp
index 2f6c069..908e19e 100644
--- a/llvm/lib/VMCore/Instructions.cpp
+++ b/llvm/lib/VMCore/Instructions.cpp
@@ -2059,8 +2059,7 @@
/// If no such cast is permited, the function returns 0.
unsigned CastInst::isEliminableCastPair(
Instruction::CastOps firstOp, Instruction::CastOps secondOp,
- Type *SrcTy, Type *MidTy, Type *DstTy, Type *IntPtrTy)
-{
+ Type *SrcTy, Type *MidTy, Type *DstTy, Type *IntPtrTy) {
// Define the 144 possibilities for these two cast instructions. The values
// in this matrix determine what to do in a given situation and select the
// case in the switch below. The rows correspond to firstOp, the columns
@@ -2113,12 +2112,16 @@
};
// If either of the casts are a bitcast from scalar to vector, disallow the
- // merging.
- if ((firstOp == Instruction::BitCast &&
- isa<VectorType>(SrcTy) != isa<VectorType>(MidTy)) ||
- (secondOp == Instruction::BitCast &&
- isa<VectorType>(MidTy) != isa<VectorType>(DstTy)))
- return 0; // Disallowed
+ // merging. However, bitcast of A->B->A are allowed.
+ bool isFirstBitcast = (firstOp == Instruction::BitCast);
+ bool isSecondBitcast = (secondOp == Instruction::BitCast);
+ bool chainedBitcast = (SrcTy == DstTy && isFirstBitcast && isSecondBitcast);
+
+ // Check if any of the bitcasts convert scalars<->vectors.
+ if ((isFirstBitcast && isa<VectorType>(SrcTy) != isa<VectorType>(MidTy)) ||
+ (isSecondBitcast && isa<VectorType>(MidTy) != isa<VectorType>(DstTy)))
+ // Unless we are bitcasing to the original type, disallow optimizations.
+ if (!chainedBitcast) return 0;
int ElimCase = CastResults[firstOp-Instruction::CastOpsBegin]
[secondOp-Instruction::CastOpsBegin];