[Mesa-dev] [PATCH v2] replace file specific compiler optimization with inline attibute

[Marc Dietrich]

File specific optimization as used for src/mesa/main/streaming-load-memcpy.c
currently will cause problems with LTO in the future
(see: https://bugs.freedesktop.org/show_bug.cgi?id=83669). Replace it with
in-file target specification.

This only works for gcc for now. The intel compiler has
__attribute__((cpu_specific(cpuid))) with cpuid core_2_duo_sse4_1, but I'm
not sure if mesa compiles with it and how it behaves on different platforms.

V2: limit support for this optimization to gcc >= 4.4 only

Signed-off-by: Marc Dietrich <marvin24 at gmx.de>
---
This is the simplest solution I see for now. Drawback is that gcc < 4.4 cannot
make use of this single improvement anymore. Otherwise we would have to maintain
a nightmare of version checks for different compilers and different pragmas.

 configure.ac                          | 10 ++++++----
 src/mesa/Makefile.am                  |  1 -
 src/mesa/main/streaming-load-memcpy.c |  4 ++--
 3 files changed, 8 insertions(+), 7 deletions(-)

diff --git a/configure.ac b/configure.ac
index 29cf32e..52ff00a 100644
--- a/configure.ac
+++ b/configure.ac
@@ -240,11 +240,13 @@ AC_SUBST([VISIBILITY_CXXFLAGS])
 dnl
 dnl Optional flags, check for compiler support
 dnl
-AX_CHECK_COMPILE_FLAG([-msse4.1], [SSE41_SUPPORTED=1], [SSE41_SUPPORTED=0])
-if test "x$SSE41_SUPPORTED" = x1; then
-    DEFINES="$DEFINES -DUSE_SSE41"
+if test 0$GCC_VERSION_MAJOR$GCC_VERSION_MINOR -ge 44; then
+    AX_CHECK_COMPILE_FLAG([-msse4.1], [SSE41_SUPPORTED=1], [SSE41_SUPPORTED=0])
+    if test "x$SSE41_SUPPORTED" = x1; then
+        DEFINES="$DEFINES -DUSE_SSE41"
+    fi
+    AM_CONDITIONAL([SSE41_SUPPORTED], [test x$SSE41_SUPPORTED = x1])
 fi
-AM_CONDITIONAL([SSE41_SUPPORTED], [test x$SSE41_SUPPORTED = x1])
 
 dnl Can't have static and shared libraries, default to static if user
 dnl explicitly requested. If both disabled, set to static since shared
diff --git a/src/mesa/Makefile.am b/src/mesa/Makefile.am
index e71bccb..bbdb36f 100644
--- a/src/mesa/Makefile.am
+++ b/src/mesa/Makefile.am
@@ -152,7 +152,6 @@ libmesagallium_la_LIBADD = \
 
 libmesa_sse41_la_SOURCES = \
 	main/streaming-load-memcpy.c
-libmesa_sse41_la_CFLAGS = $(AM_CFLAGS) -msse4.1
 
 pkgconfigdir = $(libdir)/pkgconfig
 pkgconfig_DATA = gl.pc
diff --git a/src/mesa/main/streaming-load-memcpy.c b/src/mesa/main/streaming-load-memcpy.c
index 8427149..94b0e0a 100644
--- a/src/mesa/main/streaming-load-memcpy.c
+++ b/src/mesa/main/streaming-load-memcpy.c
@@ -26,7 +26,7 @@
  *
  */
 
-#ifdef __SSE4_1__
+#ifdef USE_SSE41
 #include "main/macros.h"
 #include "main/streaming-load-memcpy.h"
 #include <smmintrin.h>
@@ -34,7 +34,7 @@
 /* Copies memory from src to dst, using SSE 4.1's MOVNTDQA to get streaming
  * read performance from uncached memory.
  */
-void
+void __attribute__ ((target("sse4.1")))
 _mesa_streaming_load_memcpy(void *restrict dst, void *restrict src, size_t len)
 {
    char *restrict d = dst;
-- 
2.1.0