[llvm] d0975b7 - [InstCombine] fold signed min/max intrinsics with negated operands

Philip Reames via llvm-commits llvm-commits at lists.llvm.org
Tue Aug 17 09:06:06 PDT 2021


It looks like this should be legal for anything which can be cheaply 
negated.  Have you looked at cases such as smax (neg nsw X), C1?

Philip

On 8/17/21 5:16 AM, Sanjay Patel via llvm-commits wrote:
> Author: Sanjay Patel
> Date: 2021-08-17T08:10:42-04:00
> New Revision: d0975b7cb0e184e8e5f3975183c51937dfa4043a
>
> URL: https://github.com/llvm/llvm-project/commit/d0975b7cb0e184e8e5f3975183c51937dfa4043a
> DIFF: https://github.com/llvm/llvm-project/commit/d0975b7cb0e184e8e5f3975183c51937dfa4043a.diff
>
> LOG: [InstCombine] fold signed min/max intrinsics with negated operands
>
> If both operands are negated, we can invert the min/max and do
> the negation after:
> smax (neg nsw X), (neg nsw Y) --> neg nsw (smin X, Y)
> smin (neg nsw X), (neg nsw Y) --> neg nsw (smax X, Y)
>
> This is visible as a remaining regression in D98152. I don't see
> a way to generalize this for 'unsigned' or adapt Negator to
> handle it. This only appears to be safe with 'nsw':
> https://alive2.llvm.org/ce/z/GUy1zJ
>
> Differential Revision: https://reviews.llvm.org/D108165
>
> Added:
>      
>
> Modified:
>      llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
>      llvm/test/Transforms/InstCombine/minmax-intrinsics.ll
>
> Removed:
>      
>
>
> ################################################################################
> diff  --git a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
> index 25597840cad3..e3dd12c0c773 100644
> --- a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
> +++ b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
> @@ -1065,6 +1065,17 @@ Instruction *InstCombinerImpl::visitCallInst(CallInst &CI) {
>         }
>       }
>   
> +    if (IID == Intrinsic::smax || IID == Intrinsic::smin) {
> +      // smax (neg nsw X), (neg nsw Y) --> neg nsw (smin X, Y)
> +      // smin (neg nsw X), (neg nsw Y) --> neg nsw (smax X, Y)
> +      if (match(I0, m_NSWNeg(m_Value(X))) && match(I1, m_NSWNeg(m_Value(Y))) &&
> +          (I0->hasOneUse() || I1->hasOneUse())) {
> +        Intrinsic::ID InvID = getInverseMinMaxIntrinsic(IID);
> +        Value *InvMaxMin = Builder.CreateBinaryIntrinsic(InvID, X, Y);
> +        return BinaryOperator::CreateNSWNeg(InvMaxMin);
> +      }
> +    }
> +
>       if (match(I0, m_Not(m_Value(X)))) {
>         // max (not X), (not Y) --> not (min X, Y)
>         Intrinsic::ID InvID = getInverseMinMaxIntrinsic(IID);
>
> diff  --git a/llvm/test/Transforms/InstCombine/minmax-intrinsics.ll b/llvm/test/Transforms/InstCombine/minmax-intrinsics.ll
> index a3dbbc9dcbde..b46ddabffd95 100644
> --- a/llvm/test/Transforms/InstCombine/minmax-intrinsics.ll
> +++ b/llvm/test/Transforms/InstCombine/minmax-intrinsics.ll
> @@ -1033,9 +1033,8 @@ define i8 @umin_demand_and_7_8(i8 %x) {
>   
>   define i8 @neg_neg_nsw_smax(i8 %x, i8 %y) {
>   ; CHECK-LABEL: @neg_neg_nsw_smax(
> -; CHECK-NEXT:    [[NX:%.*]] = sub nsw i8 0, [[X:%.*]]
> -; CHECK-NEXT:    [[NY:%.*]] = sub nsw i8 0, [[Y:%.*]]
> -; CHECK-NEXT:    [[M:%.*]] = call i8 @llvm.smax.i8(i8 [[NX]], i8 [[NY]])
> +; CHECK-NEXT:    [[TMP1:%.*]] = call i8 @llvm.smin.i8(i8 [[X:%.*]], i8 [[Y:%.*]])
> +; CHECK-NEXT:    [[M:%.*]] = sub nsw i8 0, [[TMP1]]
>   ; CHECK-NEXT:    ret i8 [[M]]
>   ;
>     %nx = sub nsw i8 0, %x
> @@ -1046,9 +1045,8 @@ define i8 @neg_neg_nsw_smax(i8 %x, i8 %y) {
>   
>   define <3 x i8> @neg_neg_nsw_smin(<3 x i8> %x, <3 x i8> %y) {
>   ; CHECK-LABEL: @neg_neg_nsw_smin(
> -; CHECK-NEXT:    [[NX:%.*]] = sub nsw <3 x i8> zeroinitializer, [[X:%.*]]
> -; CHECK-NEXT:    [[NY:%.*]] = sub nsw <3 x i8> zeroinitializer, [[Y:%.*]]
> -; CHECK-NEXT:    [[M:%.*]] = call <3 x i8> @llvm.smin.v3i8(<3 x i8> [[NX]], <3 x i8> [[NY]])
> +; CHECK-NEXT:    [[TMP1:%.*]] = call <3 x i8> @llvm.smax.v3i8(<3 x i8> [[X:%.*]], <3 x i8> [[Y:%.*]])
> +; CHECK-NEXT:    [[M:%.*]] = sub nsw <3 x i8> zeroinitializer, [[TMP1]]
>   ; CHECK-NEXT:    ret <3 x i8> [[M]]
>   ;
>     %nx = sub nsw <3 x i8> zeroinitializer, %x
> @@ -1061,8 +1059,8 @@ define i8 @neg_neg_nsw_smax_use0(i8 %x, i8 %y) {
>   ; CHECK-LABEL: @neg_neg_nsw_smax_use0(
>   ; CHECK-NEXT:    [[NX:%.*]] = sub nsw i8 0, [[X:%.*]]
>   ; CHECK-NEXT:    call void @use(i8 [[NX]])
> -; CHECK-NEXT:    [[NY:%.*]] = sub nsw i8 0, [[Y:%.*]]
> -; CHECK-NEXT:    [[M:%.*]] = call i8 @llvm.smax.i8(i8 [[NX]], i8 [[NY]])
> +; CHECK-NEXT:    [[TMP1:%.*]] = call i8 @llvm.smin.i8(i8 [[X]], i8 [[Y:%.*]])
> +; CHECK-NEXT:    [[M:%.*]] = sub nsw i8 0, [[TMP1]]
>   ; CHECK-NEXT:    ret i8 [[M]]
>   ;
>     %nx = sub nsw i8 0, %x
> @@ -1074,10 +1072,10 @@ define i8 @neg_neg_nsw_smax_use0(i8 %x, i8 %y) {
>   
>   define i8 @neg_neg_nsw_smin_use1(i8 %x, i8 %y) {
>   ; CHECK-LABEL: @neg_neg_nsw_smin_use1(
> -; CHECK-NEXT:    [[NX:%.*]] = sub nsw i8 0, [[X:%.*]]
>   ; CHECK-NEXT:    [[NY:%.*]] = sub nsw i8 0, [[Y:%.*]]
>   ; CHECK-NEXT:    call void @use(i8 [[NY]])
> -; CHECK-NEXT:    [[M:%.*]] = call i8 @llvm.smin.i8(i8 [[NX]], i8 [[NY]])
> +; CHECK-NEXT:    [[TMP1:%.*]] = call i8 @llvm.smax.i8(i8 [[X:%.*]], i8 [[Y]])
> +; CHECK-NEXT:    [[M:%.*]] = sub nsw i8 0, [[TMP1]]
>   ; CHECK-NEXT:    ret i8 [[M]]
>   ;
>     %nx = sub nsw i8 0, %x
> @@ -1087,6 +1085,8 @@ define i8 @neg_neg_nsw_smin_use1(i8 %x, i8 %y) {
>     ret i8 %m
>   }
>   
> +; negative test - too many uses
> +
>   define i8 @neg_neg_nsw_smin_use2(i8 %x, i8 %y) {
>   ; CHECK-LABEL: @neg_neg_nsw_smin_use2(
>   ; CHECK-NEXT:    [[NX:%.*]] = sub nsw i8 0, [[X:%.*]]
> @@ -1104,6 +1104,8 @@ define i8 @neg_neg_nsw_smin_use2(i8 %x, i8 %y) {
>     ret i8 %m
>   }
>   
> +; negative test - need nsw on both ops
> +
>   define i8 @neg_neg_smax(i8 %x, i8 %y) {
>   ; CHECK-LABEL: @neg_neg_smax(
>   ; CHECK-NEXT:    [[NX:%.*]] = sub i8 0, [[X:%.*]]
> @@ -1117,6 +1119,8 @@ define i8 @neg_neg_smax(i8 %x, i8 %y) {
>     ret i8 %m
>   }
>   
> +; negative test - need nsw on both ops
> +
>   define i8 @neg_neg_smin(i8 %x, i8 %y) {
>   ; CHECK-LABEL: @neg_neg_smin(
>   ; CHECK-NEXT:    [[NX:%.*]] = sub i8 0, [[X:%.*]]
> @@ -1130,6 +1134,8 @@ define i8 @neg_neg_smin(i8 %x, i8 %y) {
>     ret i8 %m
>   }
>   
> +; negative test - need signed min/max
> +
>   define i8 @neg_neg_nsw_umin(i8 %x, i8 %y) {
>   ; CHECK-LABEL: @neg_neg_nsw_umin(
>   ; CHECK-NEXT:    [[NX:%.*]] = sub nsw i8 0, [[X:%.*]]
>
>
>          
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