[InstCombine] fold bitcasts around an extractelement (3rd try)
This is a redo of r255137 (reverted at r255227) which was a redo of
r255124 (reverted at r255126) with a fixed check for a scalar source
type and an added test for the failure that caused the revert.
Original commit message:
Example:
bitcast (extractelement (bitcast <2 x float> %X to <2 x i32>), 1) to float
--->
extractelement <2 x float> %X, i32 1
This is part of fixing PR25543:
https://llvm.org/bugs/show_bug.cgi?id=25543
The next step will be to generalize this fold:
trunc ( lshr ( bitcast X) ) -> extractelement (X)
Ie, I'm hoping to replace the existing transform of:
bitcast ( trunc ( lshr ( bitcast X)))
added by:
http://reviews.llvm.org/rL112232
with 2 less specific transforms to catch the case in the bug report.
Differential Revision: http://reviews.llvm.org/D14879
llvm-svn: 255261
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
index 4afe1bb..dcd86db 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
@@ -1715,6 +1715,42 @@
return Result;
}
+/// Given a bitcasted source operand fed into an extract element instruction and
+/// then bitcasted again to a scalar type, eliminate at least one bitcast by
+/// changing the vector type of the extractelement instruction.
+/// Example:
+/// bitcast (extractelement (bitcast <2 x float> %X to <2 x i32>), 1) to float
+/// --->
+/// extractelement <2 x float> %X, i32 1
+static Instruction *foldBitCastExtElt(BitCastInst &BitCast, InstCombiner &IC,
+ const DataLayout &DL) {
+ Type *DestType = BitCast.getType();
+ if (DestType->isVectorTy())
+ return nullptr;
+
+ // TODO: Create and use a pattern matcher for ExtractElementInst.
+ auto *ExtElt = dyn_cast<ExtractElementInst>(BitCast.getOperand(0));
+ if (!ExtElt || !ExtElt->hasOneUse())
+ return nullptr;
+
+ Value *InnerBitCast = nullptr;
+ if (!match(ExtElt->getOperand(0), m_BitCast(m_Value(InnerBitCast))))
+ return nullptr;
+
+ // If the source is not a vector or its element type doesn't match the result
+ // type, bitcast it to a vector type that we can extract from.
+ Type *SourceType = InnerBitCast->getType();
+ if (SourceType->getScalarType() != DestType) {
+ unsigned VecWidth = SourceType->getPrimitiveSizeInBits();
+ unsigned DestWidth = DestType->getPrimitiveSizeInBits();
+ unsigned NumElts = VecWidth / DestWidth;
+ SourceType = VectorType::get(DestType, NumElts);
+ InnerBitCast = IC.Builder->CreateBitCast(InnerBitCast, SourceType, "bc");
+ }
+
+ return ExtractElementInst::Create(InnerBitCast, ExtElt->getOperand(1));
+}
+
static Instruction *foldVecTruncToExtElt(Value *VecInput, Type *DestTy,
unsigned ShiftAmt, InstCombiner &IC,
const DataLayout &DL) {
@@ -1886,6 +1922,9 @@
}
}
+ if (Instruction *I = foldBitCastExtElt(CI, *this, DL))
+ return I;
+
if (SrcTy->isPointerTy())
return commonPointerCastTransforms(CI);
return commonCastTransforms(CI);