[Mesa-dev] [PATCH 3/4] gallivm/ppc64le: adjust VSX code generation control.

[Ben Crocker]

In lp_build_create_jit_compiler_for_module(), advance the minimum
version of LLVM for VSX code generation to 4.0; this is the minimum
revision at which several known VSX code generation bugs are fixed:

  https://llvm.org/bugs/show_bug.cgi?id=25503 (fixed in 3.8.1)
  https://llvm.org/bugs/show_bug.cgi?id=26775 (fixed in 3.8.1)
  https://llvm.org/bugs/show_bug.cgi?id=33531 (fixed in 4.0)

An llc performance bug introduced in LLVM 4.0,

  https://llvm.org/bugs/show_bug.cgi?id=34647

is still pending as of LLVM 5.0, but only has a pronounced effect on
one of the Piglit tests: ext_transform_feedback-max-varyings.

All changes tested via Piglit.

Cc: "17.2" <mesa-stable at lists.freedesktop.org>
Signed-off-by: Ben Crocker <bcrocker at redhat.com>
---
 src/gallium/auxiliary/gallivm/lp_bld_misc.cpp | 37 ++++++++++++++++++++++-----
 1 file changed, 30 insertions(+), 7 deletions(-)

diff --git a/src/gallium/auxiliary/gallivm/lp_bld_misc.cpp b/src/gallium/auxiliary/gallivm/lp_bld_misc.cpp
index 0b43c96..644df23 100644
--- a/src/gallium/auxiliary/gallivm/lp_bld_misc.cpp
+++ b/src/gallium/auxiliary/gallivm/lp_bld_misc.cpp
@@ -628,23 +628,46 @@ lp_build_create_jit_compiler_for_module(LLVMExecutionEngineRef *OutJIT,
 #if defined(PIPE_ARCH_PPC)
    MAttrs.push_back(util_cpu_caps.has_altivec ? "+altivec" : "-altivec");
 #if (HAVE_LLVM >= 0x0304)
-#if (HAVE_LLVM <= 0x0307) || (HAVE_LLVM == 0x0308 && MESA_LLVM_VERSION_PATCH == 0)
+#if (HAVE_LLVM < 0x0400)
    /*
     * Make sure VSX instructions are disabled
-    * See LLVM bug https://llvm.org/bugs/show_bug.cgi?id=25503#c7
+    * See LLVM bugs:
+    * https://llvm.org/bugs/show_bug.cgi?id=25503#c7 (fixed in 3.8.1)
+    * https://llvm.org/bugs/show_bug.cgi?id=26775 (fixed in 3.8.1)
+    * https://llvm.org/bugs/show_bug.cgi?id=33531 (fixed in 4.0)
+    * https://llvm.org/bugs/show_bug.cgi?id=34647 (llc performance on certain unusual shader IR; intro'd in 4.0, pending as of 5.0)
     */
    if (util_cpu_caps.has_altivec) {
       MAttrs.push_back("-vsx");
    }
 #else
    /*
-    * However, bug 25503 is fixed, by the same fix that fixed
-    * bug 26775, in versions of LLVM later than 3.8 (starting with 3.8.1):
-    * Make sure VSX instructions are ENABLED
-    * See LLVM bug https://llvm.org/bugs/show_bug.cgi?id=26775
+    * Bug 25503 is fixed, by the same fix that fixed
+    * bug 26775, in versions of LLVM later than 3.8 (starting with 3.8.1).
+    * BZ 33531 actually comprises more than one bug, all of
+    * 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.
     */
    if (util_cpu_caps.has_altivec) {
-      MAttrs.push_back("+vsx");
+      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");
+      }
    }
 #endif
 #endif
-- 
2.7.4