[llvm] r323182 - [InstSimplify] (X << Y) % X -> 0

[Roman Lebedev via llvm-commits]

On Tue, Jan 23, 2018 at 12:27 PM, Anton Bikineev via llvm-commits
<llvm-commits at lists.llvm.org> wrote:
> Author: antonbikineev
> Date: Tue Jan 23 01:27:47 2018
> New Revision: 323182
>
> URL: http://llvm.org/viewvc/llvm-project?rev=323182&view=rev
> Log:
> [InstSimplify] (X << Y) % X -> 0

For future, it might be best to use `arc patch`, that way all the
commit description
is autogenerated from the differential, the link to differential is
present, etc.

> Modified:
>     llvm/trunk/lib/Analysis/InstructionSimplify.cpp
>     llvm/trunk/test/Transforms/InstSimplify/rem.ll
>
> Modified: llvm/trunk/lib/Analysis/InstructionSimplify.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/InstructionSimplify.cpp?rev=323182&r1=323181&r2=323182&view=diff
> ==============================================================================
> --- llvm/trunk/lib/Analysis/InstructionSimplify.cpp (original)
> +++ llvm/trunk/lib/Analysis/InstructionSimplify.cpp Tue Jan 23 01:27:47 2018
> @@ -1040,6 +1040,13 @@ static Value *simplifyRem(Instruction::B
>         match(Op0, m_URem(m_Value(), m_Specific(Op1)))))
>      return Op0;
>
> +  // (X << Y) % X -> 0
> +  if ((Opcode == Instruction::SRem &&
> +       match(Op0, m_NSWShl(m_Specific(Op1), m_Value()))) ||
> +      (Opcode == Instruction::URem &&
> +       match(Op0, m_NUWShl(m_Specific(Op1), m_Value()))))
> +    return Constant::getNullValue(Op0->getType());
> +
>    // If the operation is with the result of a select instruction, check whether
>    // operating on either branch of the select always yields the same value.
>    if (isa<SelectInst>(Op0) || isa<SelectInst>(Op1))
>
> Modified: llvm/trunk/test/Transforms/InstSimplify/rem.ll
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstSimplify/rem.ll?rev=323182&r1=323181&r2=323182&view=diff
> ==============================================================================
> --- llvm/trunk/test/Transforms/InstSimplify/rem.ll (original)
> +++ llvm/trunk/test/Transforms/InstSimplify/rem.ll Tue Jan 23 01:27:47 2018
> @@ -189,9 +189,7 @@ define i32 @rem4() {
>
>  define i32 @rem5(i32 %x, i32 %y) {
>  ; CHECK-LABEL: @rem5(
> -; CHECK-NEXT:    [[SHL:%.*]] = shl nsw i32 [[X:%.*]], [[Y:%.*]]
> -; CHECK-NEXT:    [[MOD:%.*]] = srem i32 [[SHL]], [[X]]
> -; CHECK-NEXT:    ret i32 [[MOD]]
> +; CHECK-NEXT:    ret i32 0
>  ;
>    %shl = shl nsw i32 %x, %y
>    %mod = srem i32 %shl, %x
> @@ -200,9 +198,7 @@ define i32 @rem5(i32 %x, i32 %y) {
>
>  define <2 x i32> @rem6(<2 x i32> %x, <2 x i32> %y) {
>  ; CHECK-LABEL: @rem6(
> -; CHECK-NEXT:    [[SHL:%.*]] = shl nsw <2 x i32> [[X:%.*]], [[Y:%.*]]
> -; CHECK-NEXT:    [[MOD:%.*]] = srem <2 x i32> [[SHL]], [[X]]
> -; CHECK-NEXT:    ret <2 x i32> [[MOD]]
> +; CHECK-NEXT:    ret <2 x i32> zeroinitializer
>  ;
>    %shl = shl nsw <2 x i32> %x, %y
>    %mod = srem <2 x i32> %shl, %x
> @@ -224,9 +220,7 @@ define i32 @rem7(i32 %x, i32 %y) {
>
>  define i32 @rem8(i32 %x, i32 %y) {
>  ; CHECK-LABEL: @rem8(
> -; CHECK-NEXT:    [[SHL:%.*]] = shl nuw i32 [[X:%.*]], [[Y:%.*]]
> -; CHECK-NEXT:    [[MOD:%.*]] = urem i32 [[SHL]], [[X]]
> -; CHECK-NEXT:    ret i32 [[MOD]]
> +; CHECK-NEXT:    ret i32 0
>  ;
>    %shl = shl nuw i32 %x, %y
>    %mod = urem i32 %shl, %x
> @@ -235,9 +229,7 @@ define i32 @rem8(i32 %x, i32 %y) {
>
>  define <2 x i32> @rem9(<2 x i32> %x, <2 x i32> %y) {
>  ; CHECK-LABEL: @rem9(
> -; CHECK-NEXT:    [[SHL:%.*]] = shl nuw <2 x i32> [[X:%.*]], [[Y:%.*]]
> -; CHECK-NEXT:    [[MOD:%.*]] = urem <2 x i32> [[SHL]], [[X]]
> -; CHECK-NEXT:    ret <2 x i32> [[MOD]]
> +; CHECK-NEXT:    ret <2 x i32> zeroinitializer
>  ;
>    %shl = shl nuw <2 x i32> %x, %y
>    %mod = urem <2 x i32> %shl, %x
>
>
> _______________________________________________
> llvm-commits mailing list
> llvm-commits at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-commits