[llvm] r176898 - ARM cost model: Increase the cost for vector casts that use the stack

[Pete Couperus]

Hello Arnold,

Is this change to work around the ARM backend's poor sext/zext v8i8 ->
v8i32 lowering (http://llvm.org/bugs/show_bug.cgi?id=14867)?
If so, maybe we should mark this as a place to revisit when that gets fixed.
I have a fix for that bug in my tree, although it may not be the best
way to fix it.

Pete



On Tue, Mar 12, 2013 at 2:19 PM, Arnold Schwaighofer
<aschwaighofer at apple.com> wrote:
> Author: arnolds
> Date: Tue Mar 12 16:19:22 2013
> New Revision: 176898
>
> URL: http://llvm.org/viewvc/llvm-project?rev=176898&view=rev
> Log:
> ARM cost model: Increase the cost for vector casts that use the stack
>
> Increase the cost of v8/v16-i8 to v8/v16-i32 casts and truncates as the backend
> currently lowers those using stack accesses.
>
> This was responsible for a significant degradation on
> MultiSource/Benchmarks/Trimaran/enc-pc1/enc-pc1
> where we vectorize one loop to a vector factor of 16. After this patch we select
> a vector factor of 4 which will generate reasonable code.
>
> unsigned char cle[32];
>
> void test(short c) {
>   unsigned short compte;
>   for (compte = 0; compte <= 31; compte++) {
>     cle[compte] = cle[compte] ^ c;
>   }
> }
>
> radar://13220512
>
> Modified:
>     llvm/trunk/lib/Target/ARM/ARMTargetTransformInfo.cpp
>     llvm/trunk/test/Analysis/CostModel/ARM/cast.ll
>
> Modified: llvm/trunk/lib/Target/ARM/ARMTargetTransformInfo.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/ARM/ARMTargetTransformInfo.cpp?rev=176898&r1=176897&r2=176898&view=diff
> ==============================================================================
> --- llvm/trunk/lib/Target/ARM/ARMTargetTransformInfo.cpp (original)
> +++ llvm/trunk/lib/Target/ARM/ARMTargetTransformInfo.cpp Tue Mar 12 16:19:22 2013
> @@ -194,6 +194,14 @@ unsigned ARMTTI::getCastInstrCost(unsign
>      { ISD::TRUNCATE,    MVT::v4i32, MVT::v4i64, 0 },
>      { ISD::TRUNCATE,    MVT::v4i16, MVT::v4i32, 1 },
>
> +    // Operations that we legalize using load/stores to the stack.
> +    { ISD::SIGN_EXTEND, MVT::v16i32, MVT::v16i8, 16*2 + 4*4 },
> +    { ISD::ZERO_EXTEND, MVT::v16i32, MVT::v16i8, 16*2 + 4*3 },
> +    { ISD::SIGN_EXTEND, MVT::v8i32, MVT::v8i8, 8*2 + 2*4 },
> +    { ISD::ZERO_EXTEND, MVT::v8i32, MVT::v8i8, 8*2 + 2*3 },
> +    { ISD::TRUNCATE,    MVT::v16i8, MVT::v16i32, 4*1 + 16*2 + 2*1 },
> +    { ISD::TRUNCATE,    MVT::v8i8, MVT::v8i32, 2*1 + 8*2 + 1 },
> +
>      // Vector float <-> i32 conversions.
>      { ISD::SINT_TO_FP,  MVT::v4f32, MVT::v4i32, 1 },
>      { ISD::UINT_TO_FP,  MVT::v4f32, MVT::v4i32, 1 },
>
> Modified: llvm/trunk/test/Analysis/CostModel/ARM/cast.ll
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Analysis/CostModel/ARM/cast.ll?rev=176898&r1=176897&r2=176898&view=diff
> ==============================================================================
> --- llvm/trunk/test/Analysis/CostModel/ARM/cast.ll (original)
> +++ llvm/trunk/test/Analysis/CostModel/ARM/cast.ll Tue Mar 12 16:19:22 2013
> @@ -152,6 +152,20 @@ define i32 @casts() {
>    ; CHECK: cost of 10 {{.*}} uitofp
>    %r69 = uitofp i64 undef to double
>
> +  ; Vector cast cost of instructions lowering the cast to the stack.
> +  ; CHECK: cost of 24 {{.*}} sext
> +  %r70 = sext <8 x i8> undef to <8 x i32>
> +  ; CHECK: cost of 48 {{.*}} sext
> +  %r71 = sext <16 x i8> undef to <16 x i32>
> +  ; CHECK: cost of 22 {{.*}} zext
> +  %r72 = zext <8 x i8> undef to <8 x i32>
> +  ; CHECK: cost of 44 {{.*}} zext
> +  %r73 = zext <16 x i8> undef to <16 x i32>
> +  ; CHECK: cost of 19 {{.*}} trunc
> +  %r74 = trunc <8 x i32> undef to <8 x i8>
> +  ; CHECK: cost of 38 {{.*}} trunc
> +  %r75 = trunc <16 x i32> undef to <16 x i8>
> +
>    ;CHECK: cost of 0 {{.*}} ret
>    ret i32 undef
>  }
>
>
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