[PATCH] R600: Fix miscompiles when BFE has multiple uses

[Tom Stellard]

On Wed, Oct 15, 2014 at 03:34:53AM +0000, Matt Arsenault wrote:
> SimplifyDemandedBits would break the other uses of the operand.
> 
> http://reviews.llvm.org/D5790
> 
> Files:
>   lib/Target/R600/AMDGPUISelLowering.cpp
>   test/CodeGen/R600/llvm.AMDGPU.bfe.u32.ll

> Index: lib/Target/R600/AMDGPUISelLowering.cpp
> ===================================================================
> --- lib/Target/R600/AMDGPUISelLowering.cpp
> +++ lib/Target/R600/AMDGPUISelLowering.cpp
> @@ -2173,13 +2173,16 @@
>                           BitsFrom, ShiftVal);
>      }
>  
> -    APInt KnownZero, KnownOne;
> -    TargetLowering::TargetLoweringOpt TLO(DAG, !DCI.isBeforeLegalize(),
> -                                          !DCI.isBeforeLegalizeOps());
> -    const TargetLowering &TLI = DAG.getTargetLoweringInfo();
> -    if (TLO.ShrinkDemandedConstant(BitsFrom, Demanded) ||
> -        TLI.SimplifyDemandedBits(BitsFrom, Demanded, KnownZero, KnownOne, TLO)) {
> -      DCI.CommitTargetLoweringOpt(TLO);
> +    if (BitsFrom.hasOneUse()) {
> +      APInt KnownZero, KnownOne;
> +      TargetLowering::TargetLoweringOpt TLO(DAG, !DCI.isBeforeLegalize(),
> +                                            !DCI.isBeforeLegalizeOps());
> +      const TargetLowering &TLI = DAG.getTargetLoweringInfo();
> +      if (TLO.ShrinkDemandedConstant(BitsFrom, Demanded) ||
> +          TLI.SimplifyDemandedBits(BitsFrom, Demanded,
> +                                   KnownZero, KnownOne, TLO)) {
> +        DCI.CommitTargetLoweringOpt(TLO);
> +      }
>      }
>  
>      break;
> Index: test/CodeGen/R600/llvm.AMDGPU.bfe.u32.ll
> ===================================================================
> --- test/CodeGen/R600/llvm.AMDGPU.bfe.u32.ll
> +++ test/CodeGen/R600/llvm.AMDGPU.bfe.u32.ll
> @@ -552,3 +552,25 @@
>    store i32 %bfe_u32, i32 addrspace(1)* %out, align 4
>    ret void
>  }
> +
> +; Make sure that SimplifyDemandedBits doesn't cause the and to be
> +; reduced to the bits demanded by the bfe.
> +
> +; XXX: The operand to v_bfe_u32 could also just directly be the load register.
> +; FUNC-LABEL: {{^}}simplify_bfe_u32_multi_use_arg

I think you need a : at the end of the function name.  Otherwise, LGTM.

-Tom

> +; SI: BUFFER_LOAD_DWORD [[ARG:v[0-9]+]]
> +; SI: V_AND_B32_e32 [[AND:v[0-9]+]], 63, [[ARG]]
> +; SI: V_BFE_U32 [[BFE:v[0-9]+]], [[AND]], 2, 2
> +; SI-DAG: BUFFER_STORE_DWORD [[AND]]
> +; SI-DAG: BUFFER_STORE_DWORD [[BFE]]
> +; SI: S_ENDPGM
> +define void @simplify_bfe_u32_multi_use_arg(i32 addrspace(1)* %out0,
> +                                            i32 addrspace(1)* %out1,
> +                                            i32 addrspace(1)* %in) nounwind {
> +  %src = load i32 addrspace(1)* %in, align 4
> +  %and = and i32 %src, 63
> +  %bfe_u32 = call i32 @llvm.AMDGPU.bfe.u32(i32 %and, i32 2, i32 2) nounwind readnone
> +  store i32 %bfe_u32, i32 addrspace(1)* %out0, align 4
> +  store i32 %and, i32 addrspace(1)* %out1, align 4
> +  ret void
> +}

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