[llvm] 8a9c70f - [InstCombine] C0 shift (X add nuw C) --> (C0 shift C) shift X

[Nikita Popov via llvm-commits]

On Tue, Apr 19, 2022 at 9:21 PM Sanjay Patel via llvm-commits <
llvm-commits at lists.llvm.org> wrote:

>
> Author: Sanjay Patel
> Date: 2022-04-19T15:21:34-04:00
> New Revision: 8a9c70fc01e6c900f060f3c23d96ee444be33a9a
>
> URL:
> https://github.com/llvm/llvm-project/commit/8a9c70fc01e6c900f060f3c23d96ee444be33a9a
> DIFF:
> https://github.com/llvm/llvm-project/commit/8a9c70fc01e6c900f060f3c23d96ee444be33a9a.diff
>
> LOG: [InstCombine] C0 shift (X add nuw C) --> (C0 shift C) shift X
>
> With 'nuw' we can convert the increment of the shift amount
> into a pre-shift (constant fold) of the shifted constant:
> https://alive2.llvm.org/ce/z/FkTyR2
>
> Fixes issue #41976
>
> Added:
>
>
> Modified:
>     llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp
>     llvm/test/Transforms/InstCombine/shift-add.ll
>
> Removed:
>
>
>
>
> ################################################################################
> diff  --git a/llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp
> b/llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp
> index 26fe8e08d066d..cc4d53d27f031 100644
> --- a/llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp
> +++ b/llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp
> @@ -399,13 +399,14 @@ Instruction
> *InstCombinerImpl::commonShiftTransforms(BinaryOperator &I) {
>            reassociateShiftAmtsOfTwoSameDirectionShifts(&I, SQ)))
>      return NewShift;
>
> -  // (C1 shift (A add C2)) -> (C1 shift C2) shift A)
> -  // iff A and C2 are both positive.
> +  // C0 shift (A add C) -> (C0 shift C) shift A
> +  // iff A and C2 are both positive or the add has 'nuw'.
>    Value *A;
>    Constant *C;
>    if (match(Op0, m_Constant()) && match(Op1, m_Add(m_Value(A),
> m_Constant(C))))
> -    if (isKnownNonNegative(A, DL, 0, &AC, &I, &DT) &&
> -        isKnownNonNegative(C, DL, 0, &AC, &I, &DT))
> +    if (cast<BinaryOperator>(Op1)->hasNoUnsignedWrap() ||
> +        (isKnownNonNegative(A, DL, 0, &AC, &I, &DT) &&
> +         isKnownNonNegative(C, DL, 0, &AC, &I, &DT)))
>        return BinaryOperator::Create(
>            I.getOpcode(), Builder.CreateBinOp(I.getOpcode(), Op0, C), A);
>

Just wondering, are those isKnownNonNegative() actually still necessary?
I'd assume that we'd infer "add nuw" from those anyway.

Nikita


>
> diff  --git a/llvm/test/Transforms/InstCombine/shift-add.ll
> b/llvm/test/Transforms/InstCombine/shift-add.ll
> index d9a1c3b1878b3..f75f6a95f8f8a 100644
> --- a/llvm/test/Transforms/InstCombine/shift-add.ll
> +++ b/llvm/test/Transforms/InstCombine/shift-add.ll
> @@ -123,8 +123,7 @@ define <4 x i32> @lshr_C1_add_A_C2_v4i32_splat(i16 %I)
> {
>
>  define i32 @shl_add_nuw(i32 %x) {
>  ; CHECK-LABEL: @shl_add_nuw(
> -; CHECK-NEXT:    [[A:%.*]] = add nuw i32 [[X:%.*]], 5
> -; CHECK-NEXT:    [[R:%.*]] = shl i32 6, [[A]]
> +; CHECK-NEXT:    [[R:%.*]] = shl i32 192, [[X:%.*]]
>  ; CHECK-NEXT:    ret i32 [[R]]
>  ;
>    %a = add nuw i32 %x, 5
> @@ -132,10 +131,11 @@ define i32 @shl_add_nuw(i32 %x) {
>    ret i32 %r
>  }
>
> +; vectors with arbitrary constants work too
> +
>  define <2 x i12> @lshr_add_nuw(<2 x i12> %x) {
>  ; CHECK-LABEL: @lshr_add_nuw(
> -; CHECK-NEXT:    [[A:%.*]] = add nuw <2 x i12> [[X:%.*]], <i12 5, i12 1>
> -; CHECK-NEXT:    [[R:%.*]] = lshr <2 x i12> <i12 6, i12 42>, [[A]]
> +; CHECK-NEXT:    [[R:%.*]] = lshr <2 x i12> <i12 0, i12 21>, [[X:%.*]]
>  ; CHECK-NEXT:    ret <2 x i12> [[R]]
>  ;
>    %a = add nuw <2 x i12> %x, <i12 5, i12 1>
> @@ -143,12 +143,13 @@ define <2 x i12> @lshr_add_nuw(<2 x i12> %x) {
>    ret <2 x i12> %r
>  }
>
> +; extra use is ok and in this case the result can be simplified to a
> constant
> +
>  define i32 @ashr_add_nuw(i32 %x, i32* %p) {
>  ; CHECK-LABEL: @ashr_add_nuw(
>  ; CHECK-NEXT:    [[A:%.*]] = add nuw i32 [[X:%.*]], 5
>  ; CHECK-NEXT:    store i32 [[A]], i32* [[P:%.*]], align 4
> -; CHECK-NEXT:    [[R:%.*]] = ashr i32 -6, [[A]]
> -; CHECK-NEXT:    ret i32 [[R]]
> +; CHECK-NEXT:    ret i32 -1
>  ;
>    %a = add nuw i32 %x, 5
>    store i32 %a, i32* %p
> @@ -156,6 +157,8 @@ define i32 @ashr_add_nuw(i32 %x, i32* %p) {
>    ret i32 %r
>  }
>
> +; negative test - must have 'nuw'
> +
>  define i32 @shl_add_nsw(i32 %x) {
>  ; CHECK-LABEL: @shl_add_nsw(
>  ; CHECK-NEXT:    [[A:%.*]] = add nsw i32 [[X:%.*]], 5
>
>
>
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