[PATCH] D30123: [InstCombine] shrink truncated splat shuffle

[Zachary Turner via llvm-commits]

Are you looking into all the failures?

http://lab.llvm.org:8011/builders/clang-cmake-aarch64-quick/builds/4406

On Tue, Mar 7, 2017 at 8:30 AM Sanjay Patel via Phabricator via
llvm-commits <llvm-commits at lists.llvm.org> wrote:

> This revision was automatically updated to reflect the committed changes.
> Closed by commit rL297155: [InstCombine] shrink truncated splat shuffle
> (authored by spatel).
>
> Changed prior to commit:
>   https://reviews.llvm.org/D30123?vs=89025&id=90857#toc
>
> Repository:
>   rL LLVM
>
> https://reviews.llvm.org/D30123
>
> Files:
>   llvm/trunk/lib/Transforms/InstCombine/InstCombineCasts.cpp
>   llvm/trunk/test/Transforms/InstCombine/trunc.ll
>
>
> Index: llvm/trunk/test/Transforms/InstCombine/trunc.ll
> ===================================================================
> --- llvm/trunk/test/Transforms/InstCombine/trunc.ll
> +++ llvm/trunk/test/Transforms/InstCombine/trunc.ll
> @@ -478,28 +478,26 @@
>    ret <4 x i8> %trunc
>  }
>
> -; FIXME:
>  ; trunc (shuffle X, undef, SplatMask) --> shuffle (trunc X), undef,
> SplatMask
>
>  define <4 x i8> @wide_splat1(<4 x i32> %x) {
>  ; CHECK-LABEL: @wide_splat1(
> -; CHECK-NEXT:    [[SHUF:%.*]] = shufflevector <4 x i32> %x, <4 x i32>
> undef, <4 x i32> <i32 2, i32 2, i32 2, i32 2>
> -; CHECK-NEXT:    [[TRUNC:%.*]] = trunc <4 x i32> [[SHUF]] to <4 x i8>
> +; CHECK-NEXT:    [[TMP1:%.*]] = trunc <4 x i32> %x to <4 x i8>
> +; CHECK-NEXT:    [[TRUNC:%.*]] = shufflevector <4 x i8> [[TMP1]], <4 x
> i8> undef, <4 x i32> <i32 2, i32 2, i32 2, i32 2>
>  ; CHECK-NEXT:    ret <4 x i8> [[TRUNC]]
>  ;
>    %shuf = shufflevector <4 x i32> %x, <4 x i32> undef, <4 x i32> <i32 2,
> i32 2, i32 2, i32 2>
>    %trunc = trunc <4 x i32> %shuf to <4 x i8>
>    ret <4 x i8> %trunc
>  }
>
> -; FIXME:
>  ; Test weird types.
>  ; trunc (shuffle X, undef, SplatMask) --> shuffle (trunc X), undef,
> SplatMask
>
>  define <3 x i31> @wide_splat2(<3 x i33> %x) {
>  ; CHECK-LABEL: @wide_splat2(
> -; CHECK-NEXT:    [[SHUF:%.*]] = shufflevector <3 x i33> %x, <3 x i33>
> undef, <3 x i32> <i32 1, i32 1, i32 1>
> -; CHECK-NEXT:    [[TRUNC:%.*]] = trunc <3 x i33> [[SHUF]] to <3 x i31>
> +; CHECK-NEXT:    [[TMP1:%.*]] = trunc <3 x i33> %x to <3 x i31>
> +; CHECK-NEXT:    [[TRUNC:%.*]] = shufflevector <3 x i31> [[TMP1]], <3 x
> i31> undef, <3 x i32> <i32 1, i32 1, i32 1>
>  ; CHECK-NEXT:    ret <3 x i31> [[TRUNC]]
>  ;
>    %shuf = shufflevector <3 x i33> %x, <3 x i33> undef, <3 x i32> <i32 1,
> i32 1, i32 1>
> Index: llvm/trunk/lib/Transforms/InstCombine/InstCombineCasts.cpp
> ===================================================================
> --- llvm/trunk/lib/Transforms/InstCombine/InstCombineCasts.cpp
> +++ llvm/trunk/lib/Transforms/InstCombine/InstCombineCasts.cpp
> @@ -463,6 +463,23 @@
>    return BinaryOperator::Create(LogicOp->getOpcode(), NarrowOp0, NarrowC);
>  }
>
> +/// Try to narrow the width of a splat shuffle. This could be generalized
> to any
> +/// shuffle with a constant operand, but we limit the transform to avoid
> +/// creating a shuffle type that targets may not be able to lower
> effectively.
> +static Instruction *shrinkSplatShuffle(TruncInst &Trunc,
> +                                       InstCombiner::BuilderTy &Builder) {
> +  auto *Shuf = dyn_cast<ShuffleVectorInst>(Trunc.getOperand(0));
> +  if (Shuf && Shuf->hasOneUse() && isa<UndefValue>(Shuf->getOperand(1)) &&
> +      Shuf->getMask()->getSplatValue()) {
> +    // trunc (shuf X, Undef, SplatMask) --> shuf (trunc X), Undef,
> SplatMask
> +    Constant *NarrowUndef = UndefValue::get(Trunc.getType());
> +    Value *NarrowOp = Builder.CreateTrunc(Shuf->getOperand(0),
> Trunc.getType());
> +    return new ShuffleVectorInst(NarrowOp, NarrowUndef, Shuf->getMask());
> +  }
> +
> +  return nullptr;
> +}
> +
>  Instruction *InstCombiner::visitTrunc(TruncInst &CI) {
>    if (Instruction *Result = commonCastTransforms(CI))
>      return Result;
> @@ -554,6 +571,9 @@
>    if (Instruction *I = shrinkBitwiseLogic(CI))
>      return I;
>
> +  if (Instruction *I = shrinkSplatShuffle(CI, *Builder))
> +    return I;
> +
>    if (Src->hasOneUse() && isa<IntegerType>(SrcTy) &&
>        shouldChangeType(SrcTy, DestTy)) {
>      // Transform "trunc (shl X, cst)" -> "shl (trunc X), cst" so long as
> the
>
>
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