[Mesa-dev] [PATCH 08/10] radeonsi: re-enable unsafe-fp-math for LLVM 3.8

[Connor Abbott]

FWIW, this isn't quite correct with ARB_shader_precision or GL4.1 --
it specifies that infinities should be correctly generated through
division by 0, which unsafe-fp-math doesn't guarantee. At least,
that's assuming this is similar to the "fast" per-instruction flag
(http://llvm.org/docs/LangRef.html#fast-math-flags) which says "This
flag implies all the others."

On Sat, Oct 10, 2015 at 9:29 PM, Marek Olšák <maraeo at gmail.com> wrote:
> From: Marek Olšák <marek.olsak at amd.com>
>
> Required for 1/sqrt ==> rsq.
>
> We should finally fix the hang instead of running away from the issue. This
> assumes the bug is in LLVM and we have time to fix it before the release.
> Include compute shaders as well, which only affects TGSI and thus OpenGL.
>
> Totals:
> SGPRS: 344368 -> 345104 (0.21 %)
> VGPRS: 197552 -> 197420 (-0.07 %)
> Code Size: 7366304 -> 7324692 (-0.56 %) bytes
> LDS: 91 -> 91 (0.00 %) blocks
> Scratch: 1615872 -> 1524736 (-5.64 %) bytes per wave
>
> Totals from affected shaders:
> SGPRS: 146696 -> 147432 (0.50 %)
> VGPRS: 87212 -> 87080 (-0.15 %)
> Code Size: 3852664 -> 3811052 (-1.08 %) bytes
> LDS: 48 -> 48 (0.00 %) blocks
> Scratch: 1179648 -> 1088512 (-7.73 %) bytes per wave
> ---
>  src/gallium/drivers/radeon/radeon_llvm_emit.c | 7 +++++++
>  1 file changed, 7 insertions(+)
>
> diff --git a/src/gallium/drivers/radeon/radeon_llvm_emit.c b/src/gallium/drivers/radeon/radeon_llvm_emit.c
> index 6b2ebde..4bda4a4 100644
> --- a/src/gallium/drivers/radeon/radeon_llvm_emit.c
> +++ b/src/gallium/drivers/radeon/radeon_llvm_emit.c
> @@ -84,6 +84,13 @@ void radeon_llvm_shader_type(LLVMValueRef F, unsigned type)
>         sprintf(Str, "%1d", llvm_type);
>
>         LLVMAddTargetDependentFunctionAttr(F, "ShaderType", Str);
> +
> +#if HAVE_LLVM >= 0x0308
> +       /* This only affects TGSI (OpenGL), so it's okay to set it for
> +        * compute shaders too.
> +        */
> +       LLVMAddTargetDependentFunctionAttr(F, "unsafe-fp-math", "true");
> +#endif
>  }
>
>  static void init_r600_target()
> --
> 2.1.4
>
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