[Mesa-dev] [PATCH] gallivm: Detect VSX separately from Altivec

[Roland Scheidegger]

u_cpu_detect should detect what's really available, not what is used
(though indeed we actually disable u_cpu bits explicitly in gallivm for
some sse features, but this is a hack).
So I think it would be better if u_cpu_detect sets the has_vsx bit
regardless what the env var is and then enable it based on this bit and
the env var.
Otherwise looks good to me.

Roland

Am 19.08.2018 um 23:17 schrieb Vicki Pfau:
> Previously gallivm would attempt to use VSX instructions on all systems
> where it detected that Altivec is supported; however, VSX was added to
> POWER long after Altivec, causing lots of crashes on older POWER/PPC
> hardware, e.g. PPC Macs. By detecting VSX separately from Altivec we can
> automatically disable it on hardware that supports Altivec but not VSX
> 
> Signed-off-by: Vicki Pfau <vi at endrift.com>
> ---
>  src/gallium/auxiliary/gallivm/lp_bld_misc.cpp | 21 +++----------------
>  src/gallium/auxiliary/util/u_cpu_detect.c     | 14 ++++++++++++-
>  src/gallium/auxiliary/util/u_cpu_detect.h     |  1 +
>  3 files changed, 17 insertions(+), 19 deletions(-)
> 
> diff --git a/src/gallium/auxiliary/gallivm/lp_bld_misc.cpp b/src/gallium/auxiliary/gallivm/lp_bld_misc.cpp
> index 79dbedbb56..fcbdd5050f 100644
> --- a/src/gallium/auxiliary/gallivm/lp_bld_misc.cpp
> +++ b/src/gallium/auxiliary/gallivm/lp_bld_misc.cpp
> @@ -650,26 +650,11 @@ lp_build_create_jit_compiler_for_module(LLVMExecutionEngineRef *OutJIT,
>      * which are fixed in LLVM 4.0.
>      *
>      * With LLVM 4.0 or higher:
> -    * Make sure VSX instructions are ENABLED, unless
> -    * a) the entire -mattr option is overridden via GALLIVM_MATTRS, or
> -    * b) VSX instructions are explicitly enabled/disabled via GALLIVM_VSX=1 or 0.
> +    * Make sure VSX instructions are ENABLED (if supported), unless
> +    * VSX instructions are explicitly enabled/disabled via GALLIVM_VSX=1 or 0.
>      */
>     if (util_cpu_caps.has_altivec) {
> -      char *env_mattrs = getenv("GALLIVM_MATTRS");
> -      if (env_mattrs) {
> -         MAttrs.push_back(env_mattrs);
> -      }
> -      else {
> -         boolean enable_vsx = true;
> -         char *env_vsx = getenv("GALLIVM_VSX");
> -         if (env_vsx && env_vsx[0] == '0') {
> -            enable_vsx = false;
> -         }
> -         if (enable_vsx)
> -            MAttrs.push_back("+vsx");
> -         else
> -            MAttrs.push_back("-vsx");
> -      }
> +      MAttrs.push_back(util_cpu_caps.has_vsx ? "+vsx" : "-vsx");
>     }
>  #endif
>  #endif
> diff --git a/src/gallium/auxiliary/util/u_cpu_detect.c b/src/gallium/auxiliary/util/u_cpu_detect.c
> index 3c6ae4ea1a..14003aa769 100644
> --- a/src/gallium/auxiliary/util/u_cpu_detect.c
> +++ b/src/gallium/auxiliary/util/u_cpu_detect.c
> @@ -133,6 +133,7 @@ check_os_altivec_support(void)
>        signal(SIGILL, SIG_DFL);
>     } else {
>        boolean enable_altivec = TRUE;    /* Default: enable  if available, and if not overridden */
> +      boolean enable_vsx = TRUE;
>  #ifdef DEBUG
>        /* Disabling Altivec code generation is not the same as disabling VSX code generation,
>         * which can be done simply by passing -mattr=-vsx to the LLVM compiler; cf.
> @@ -144,6 +145,11 @@ check_os_altivec_support(void)
>           enable_altivec = FALSE;
>        }
>  #endif
> +      /* VSX instructions can be explicitly enabled/disabled via GALLIVM_VSX=1 or 0 */
> +      char *env_vsx = getenv("GALLIVM_VSX");
> +      if (env_vsx && env_vsx[0] == '0') {
> +         enable_vsx = FALSE;
> +      }
>        if (enable_altivec) {
>           __lv_powerpc_canjump = 1;
>  
> @@ -153,8 +159,13 @@ check_os_altivec_support(void)
>               :
>               : "r" (-1));
>  
> -         signal(SIGILL, SIG_DFL);
>           util_cpu_caps.has_altivec = 1;
> +
> +         if (enable_vsx) {
> +            __asm __volatile("xxland %vs0, %vs0, %vs0");
> +            util_cpu_caps.has_vsx = 1;
> +         }
> +         signal(SIGILL, SIG_DFL);
>        } else {
>           util_cpu_caps.has_altivec = 0;
>        }
> @@ -536,6 +547,7 @@ util_cpu_detect(void)
>        debug_printf("util_cpu_caps.has_3dnow_ext = %u\n", util_cpu_caps.has_3dnow_ext);
>        debug_printf("util_cpu_caps.has_xop = %u\n", util_cpu_caps.has_xop);
>        debug_printf("util_cpu_caps.has_altivec = %u\n", util_cpu_caps.has_altivec);
> +      debug_printf("util_cpu_caps.has_vsx = %u\n", util_cpu_caps.has_vsx);
>        debug_printf("util_cpu_caps.has_neon = %u\n", util_cpu_caps.has_neon);
>        debug_printf("util_cpu_caps.has_daz = %u\n", util_cpu_caps.has_daz);
>        debug_printf("util_cpu_caps.has_avx512f = %u\n", util_cpu_caps.has_avx512f);
> diff --git a/src/gallium/auxiliary/util/u_cpu_detect.h b/src/gallium/auxiliary/util/u_cpu_detect.h
> index 7a63d55028..19f5567ca7 100644
> --- a/src/gallium/auxiliary/util/u_cpu_detect.h
> +++ b/src/gallium/auxiliary/util/u_cpu_detect.h
> @@ -71,6 +71,7 @@ struct util_cpu_caps {
>     unsigned has_3dnow_ext:1;
>     unsigned has_xop:1;
>     unsigned has_altivec:1;
> +   unsigned has_vsx:1;
>     unsigned has_daz:1;
>     unsigned has_neon:1;
>  
>