[llvm] r255261 - [InstCombine] fold bitcasts around an extractelement (3rd try)
Sanjay Patel via llvm-commits
llvm-commits at lists.llvm.org
Thu Dec 10 09:09:28 PST 2015
Author: spatel
Date: Thu Dec 10 11:09:28 2015
New Revision: 255261
URL: http://llvm.org/viewvc/llvm-project?rev=255261&view=rev
Log:
[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
Modified:
llvm/trunk/lib/Transforms/InstCombine/InstCombineCasts.cpp
llvm/trunk/test/Transforms/InstCombine/bitcast.ll
Modified: llvm/trunk/lib/Transforms/InstCombine/InstCombineCasts.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstCombineCasts.cpp?rev=255261&r1=255260&r2=255261&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/InstCombine/InstCombineCasts.cpp (original)
+++ llvm/trunk/lib/Transforms/InstCombine/InstCombineCasts.cpp Thu Dec 10 11:09:28 2015
@@ -1715,6 +1715,42 @@ static Value *optimizeIntegerToVectorIns
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 @@ Instruction *InstCombiner::visitBitCast(
}
}
+ if (Instruction *I = foldBitCastExtElt(CI, *this, DL))
+ return I;
+
if (SrcTy->isPointerTy())
return commonPointerCastTransforms(CI);
return commonCastTransforms(CI);
Modified: llvm/trunk/test/Transforms/InstCombine/bitcast.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/bitcast.ll?rev=255261&r1=255260&r2=255261&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/bitcast.ll (original)
+++ llvm/trunk/test/Transforms/InstCombine/bitcast.ll Thu Dec 10 11:09:28 2015
@@ -64,7 +64,7 @@ define float @test3(<2 x float> %A, <2 x
; CHECK-NEXT: ret float %add
}
-; TODO: Both bitcasts are unnecessary; change the extractelement.
+; Both bitcasts are unnecessary; change the extractelement.
define float @bitcast_extelt1(<2 x float> %A) {
%bc1 = bitcast <2 x float> %A to <2 x i32>
@@ -73,13 +73,11 @@ define float @bitcast_extelt1(<2 x float
ret float %bc2
; CHECK-LABEL: @bitcast_extelt1(
-; CHECK-NEXT: %bc1 = bitcast <2 x float> %A to <2 x i32>
-; CHECK-NEXT: %ext = extractelement <2 x i32> %bc1, i32 0
-; CHECK-NEXT: %bc2 = bitcast i32 %ext to float
+; CHECK-NEXT: %bc2 = extractelement <2 x float> %A, i32 0
; CHECK-NEXT: ret float %bc2
}
-; TODO: Second bitcast can be folded into the first.
+; Second bitcast can be folded into the first.
define i64 @bitcast_extelt2(<4 x float> %A) {
%bc1 = bitcast <4 x float> %A to <2 x double>
@@ -88,12 +86,40 @@ define i64 @bitcast_extelt2(<4 x float>
ret i64 %bc2
; CHECK-LABEL: @bitcast_extelt2(
-; CHECK-NEXT: %bc1 = bitcast <4 x float> %A to <2 x double>
-; CHECK-NEXT: %ext = extractelement <2 x double> %bc1, i32 1
-; CHECK-NEXT: %bc2 = bitcast double %ext to i64
+; CHECK-NEXT: %bc = bitcast <4 x float> %A to <2 x i64>
+; CHECK-NEXT: %bc2 = extractelement <2 x i64> %bc, i32 1
; CHECK-NEXT: ret i64 %bc2
}
+; TODO: This should return %A.
+
+define <2 x i32> @bitcast_extelt3(<2 x i32> %A) {
+ %bc1 = bitcast <2 x i32> %A to <1 x i64>
+ %ext = extractelement <1 x i64> %bc1, i32 0
+ %bc2 = bitcast i64 %ext to <2 x i32>
+ ret <2 x i32> %bc2
+
+; CHECK-LABEL: @bitcast_extelt3(
+; CHECK-NEXT: %bc1 = bitcast <2 x i32> %A to <1 x i64>
+; CHECK-NEXT: %ext = extractelement <1 x i64> %bc1, i32 0
+; CHECK-NEXT: %bc2 = bitcast i64 %ext to <2 x i32>
+; CHECK-NEXT: ret <2 x i32> %bc2
+}
+
+; Handle the case where the input is not a vector.
+
+define double @bitcast_extelt4(i128 %A) {
+ %bc1 = bitcast i128 %A to <2 x i64>
+ %ext = extractelement <2 x i64> %bc1, i32 0
+ %bc2 = bitcast i64 %ext to double
+ ret double %bc2
+
+; CHECK-LABEL: @bitcast_extelt4(
+; CHECK-NEXT: %bc = bitcast i128 %A to <2 x double>
+; CHECK-NEXT: %bc2 = extractelement <2 x double> %bc, i32 0
+; CHECK-NEXT: ret double %bc2
+}
+
define <2 x i32> @test4(i32 %A, i32 %B){
%tmp38 = zext i32 %A to i64
%tmp32 = zext i32 %B to i64
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