[Mesa-stable] [PATCH 4/4] gallivm/ppc64le: allow environmental control of Altivec code generation

[Ben Crocker]

In check_os_altivec_support(), allow control of Altivec (first PPC vector
instruction set) code generation via a new environmental control,
GALLIVM_ALTIVEC, which is expected to take on a value of 1 or 0.
The default is to enable Altivec code generation.

This environmental control of Altivec code generation is initially
available only #ifdef DEBUG.

Cc: "17.2" <mesa-stable at lists.freedesktop.org>
Signed-off-by: Ben Crocker <bcrocker at redhat.com>
---
 src/gallium/auxiliary/util/u_cpu_detect.c | 32 +++++++++++++++++++++++--------
 1 file changed, 24 insertions(+), 8 deletions(-)

diff --git a/src/gallium/auxiliary/util/u_cpu_detect.c b/src/gallium/auxiliary/util/u_cpu_detect.c
index 4e71041..6a59f27 100644
--- a/src/gallium/auxiliary/util/u_cpu_detect.c
+++ b/src/gallium/auxiliary/util/u_cpu_detect.c
@@ -132,16 +132,32 @@ check_os_altivec_support(void)
    if (setjmp(__lv_powerpc_jmpbuf)) {
       signal(SIGILL, SIG_DFL);
    } else {
-      __lv_powerpc_canjump = 1;
+      boolean enable_altivec = TRUE;    /* Default: enable  if available, and if not overridden */
+#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.
+       * lp_build_create_jit_compiler_for_module().
+       * If you want to disable Altivec code generation, the best place to do it is here.
+       */
+      char *env_control = getenv("GALLIVM_ALTIVEC");    /* 1=enable (default); 0=disable */
+      if (env_control && env_control[0] == '0') {
+         enable_altivec = FALSE;
+      }
+#endif
+      if (enable_altivec) {
+         __lv_powerpc_canjump = 1;
 
-      __asm __volatile
-         ("mtspr 256, %0\n\t"
-          "vand %%v0, %%v0, %%v0"
-          :
-          : "r" (-1));
+         __asm __volatile
+            ("mtspr 256, %0\n\t"
+             "vand %%v0, %%v0, %%v0"
+             :
+             : "r" (-1));
 
-      signal(SIGILL, SIG_DFL);
-      util_cpu_caps.has_altivec = 1;
+         signal(SIGILL, SIG_DFL);
+         util_cpu_caps.has_altivec = 1;
+      } else {
+         util_cpu_caps.has_altivec = 0;
+      }
    }
 #endif /* !PIPE_OS_APPLE */
 }
-- 
2.7.4