[InstCombine] allow any pair of bitcasts to be combined
This change is discussed in D15392 and should allow us to effectively
revert:
http://llvm.org/viewvc/llvm-project?view=revision&revision=255261
if we canonicalize bitcasts ahead of extracts.
It should be safe to convert any pair of bitcasts into a single bitcast,
however, it was mentioned here:
http://lists.llvm.org/pipermail/llvm-commits/Week-of-Mon-20110829/127089.html
that we're not allowed to bitcast from an x86_mmx to some other types, but I'm
not seeing any failures from that, and we have regression tests in CodeGen/X86
that appear to cover all of those cases.
Some day we'll get to remove that MMX wart from LLVM IR completely?
Differential Revision: http://reviews.llvm.org/D15468
llvm-svn: 255399
diff --git a/llvm/lib/IR/Instructions.cpp b/llvm/lib/IR/Instructions.cpp
index 8399082..11c5586 100644
--- a/llvm/lib/IR/Instructions.cpp
+++ b/llvm/lib/IR/Instructions.cpp
@@ -2516,17 +2516,19 @@
{ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,13,12}, // AddrSpaceCast -+
};
+ // TODO: This logic could be encoded into the table above and handled in the
+ // switch below.
// If either of the casts are a bitcast from scalar to vector, disallow the
- // 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);
+ // merging. However, any pair of bitcasts are allowed.
+ bool IsFirstBitcast = (firstOp == Instruction::BitCast);
+ bool IsSecondBitcast = (secondOp == Instruction::BitCast);
+ bool AreBothBitcasts = 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 bitcasting to the original type, disallow optimizations.
- if (!chainedBitcast) return 0;
+ // Check if any of the casts convert scalars <-> vectors.
+ if ((IsFirstBitcast && isa<VectorType>(SrcTy) != isa<VectorType>(MidTy)) ||
+ (IsSecondBitcast && isa<VectorType>(MidTy) != isa<VectorType>(DstTy)))
+ if (!AreBothBitcasts)
+ return 0;
int ElimCase = CastResults[firstOp-Instruction::CastOpsBegin]
[secondOp-Instruction::CastOpsBegin];