[llvm] r255137 - [InstCombine] fold bitcasts around an extractelement (2nd try)
Akira Hatanaka via llvm-commits
llvm-commits at lists.llvm.org
Thu Dec 10 00:07:51 PST 2015
Hi Sanjay,
I reverted this in r255227.
This causes an assert when the following IR is compiled with "opt
-instcombine":
define internal double @foo1(<2 x double> %a) {
%1 = bitcast <2 x double> %a to i128
%2 = bitcast i128 %1 to <2 x i64>
%3 = extractelement <2 x i64> %2, i32 0
%4 = bitcast i64 %3 to double
ret double %4
}
On Wed, Dec 9, 2015 at 10:57 AM, Sanjay Patel via llvm-commits <
llvm-commits at lists.llvm.org> wrote:
> Author: spatel
> Date: Wed Dec 9 12:57:16 2015
> New Revision: 255137
>
> URL: http://llvm.org/viewvc/llvm-project?rev=255137&view=rev
> Log:
> [InstCombine] fold bitcasts around an extractelement (2nd try)
>
> This is a redo of r255124 (reverted at r255126) with an added check for a
> scalar destination type and an added test for the failure seen in Clang's
> test/CodeGen/vector.c. The extra test shows a different missing
> optimization.
>
> 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=255137&r1=255136&r2=255137&view=diff
>
> ==============================================================================
> --- llvm/trunk/lib/Transforms/InstCombine/InstCombineCasts.cpp (original)
> +++ llvm/trunk/lib/Transforms/InstCombine/InstCombineCasts.cpp Wed Dec 9
> 12:57:16 2015
> @@ -1715,6 +1715,42 @@ static Value *optimizeIntegerToVectorIns
> return Result;
> }
>
> +/// Given a bitcasted vector 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 element type of the vector doesn't match the result type,
> + // bitcast it to a vector type that we can extract from.
> + VectorType *VecType = cast<VectorType>(InnerBitCast->getType());
> + if (VecType->getElementType() != DestType) {
> + unsigned VecWidth = VecType->getPrimitiveSizeInBits();
> + unsigned DestWidth = DestType->getPrimitiveSizeInBits();
> + unsigned NumElts = VecWidth / DestWidth;
> + VecType = VectorType::get(DestType, NumElts);
> + InnerBitCast = IC.Builder->CreateBitCast(InnerBitCast, VecType, "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=255137&r1=255136&r2=255137&view=diff
>
> ==============================================================================
> --- llvm/trunk/test/Transforms/InstCombine/bitcast.ll (original)
> +++ llvm/trunk/test/Transforms/InstCombine/bitcast.ll Wed Dec 9 12:57:16
> 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 +86,26 @@ 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
> +}
> +
> 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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