[Mesa-dev] [PATCH] util: try much harder to set DAZ flag

[sroland at vmware.com]

From: Roland Scheidegger <sroland at vmware.com>

While so far this only causes some harmless test failures, there's lots more
cpus with DAZ. All 64bit capable ones can do it (particularly relevant for
AMD cpus as they supported sse3 very very late) but if really necessary we
can check support for that for real with some more magic.
(In fact just about ANY cpu with sse2 can support DAZ, I believe the only
exception are first gen P4 (Willamette) and from those only early steppings
which can't do it it's almost like intel forgot to add it... - a real pity
though docs say you can't just try to set it as they will throw a GPF.)
This addresses https://bugs.freedesktop.org/show_bug.cgi?id=67672 though
I'm not convinced this is relevant enough for 9.2. Might want to fix the
tests instead...
---
 src/gallium/auxiliary/util/u_cpu_detect.c |   29 +++++++++++++++++++++++++++++
 src/gallium/auxiliary/util/u_cpu_detect.h |    1 +
 src/gallium/auxiliary/util/u_math.c       |    2 +-
 3 files changed, 31 insertions(+), 1 deletion(-)

diff --git a/src/gallium/auxiliary/util/u_cpu_detect.c b/src/gallium/auxiliary/util/u_cpu_detect.c
index 588fc7c..c58a3dd 100644
--- a/src/gallium/auxiliary/util/u_cpu_detect.c
+++ b/src/gallium/auxiliary/util/u_cpu_detect.c
@@ -230,8 +230,28 @@ static INLINE uint64_t xgetbv(void)
 #else
    return 0;
 #endif
+}
+
 
+#if defined(PIPE_ARCH_X86)
+static INLINE boolean sse2_has_daz(void)
+{
+   struct {
+      uint32_t pad1[7];
+      uint32_t mxcsr_mask;
+      uint32_t pad2[128-8];
+   } PIPE_ALIGN_VAR(16) fxarea;
+
+   fxarea.mxcsr_mask = 0;
+#if (defined(PIPE_CC_GCC) || defined(PIPE_CC_SUNPRO))
+   asm volatile ("fxsave %0" :: "m" (fxarea));
+#elif (defined(PIPE_CC_MSVC) || defined(PIPE_CC_ICL))
+   _fxsave(fxarea);
+#endif
+   return !!(fxarea.mxcsr_mask & (1 << 6));
 }
+#endif
+
 #endif /* X86 or X86_64 */
 
 void
@@ -310,6 +330,12 @@ util_cpu_detect(void)
                                     ((xgetbv() & 6) == 6);    // XMM & YMM
          util_cpu_caps.has_f16c   = (regs2[2] >> 29) & 1;
          util_cpu_caps.has_mmx2   = util_cpu_caps.has_sse; /* SSE cpus supports mmxext too */
+#if defined(PIPE_ARCH_X86_64)
+         util_cpu_caps.has_daz = 1;
+#else
+         util_cpu_caps.has_daz = util_cpu_caps.has_sse3 ||
+            (util_cpu_caps.has_sse2 && sse2_has_daz());
+#endif
 
          cacheline = ((regs2[1] >> 8) & 0xFF) * 8;
          if (cacheline > 0)
@@ -368,9 +394,12 @@ util_cpu_detect(void)
       debug_printf("util_cpu_caps.has_sse4_1 = %u\n", util_cpu_caps.has_sse4_1);
       debug_printf("util_cpu_caps.has_sse4_2 = %u\n", util_cpu_caps.has_sse4_2);
       debug_printf("util_cpu_caps.has_avx = %u\n", util_cpu_caps.has_avx);
+      debug_printf("util_cpu_caps.has_f16c = %u\n", util_cpu_caps.has_f16c);
+      debug_printf("util_cpu_caps.has_popcnt = %u\n", util_cpu_caps.has_popcnt);
       debug_printf("util_cpu_caps.has_3dnow = %u\n", util_cpu_caps.has_3dnow);
       debug_printf("util_cpu_caps.has_3dnow_ext = %u\n", util_cpu_caps.has_3dnow_ext);
       debug_printf("util_cpu_caps.has_altivec = %u\n", util_cpu_caps.has_altivec);
+      debug_printf("util_cpu_caps.has_daz = %u\n", util_cpu_caps.has_daz);
    }
 #endif
 
diff --git a/src/gallium/auxiliary/util/u_cpu_detect.h b/src/gallium/auxiliary/util/u_cpu_detect.h
index f9cd647..cc3e0ce 100644
--- a/src/gallium/auxiliary/util/u_cpu_detect.h
+++ b/src/gallium/auxiliary/util/u_cpu_detect.h
@@ -68,6 +68,7 @@ struct util_cpu_caps {
    unsigned has_3dnow:1;
    unsigned has_3dnow_ext:1;
    unsigned has_altivec:1;
+   unsigned has_daz:1;
 };
 
 extern struct util_cpu_caps
diff --git a/src/gallium/auxiliary/util/u_math.c b/src/gallium/auxiliary/util/u_math.c
index f3fe392..6981ee9 100644
--- a/src/gallium/auxiliary/util/u_math.c
+++ b/src/gallium/auxiliary/util/u_math.c
@@ -111,7 +111,7 @@ util_fpstate_set_denorms_to_zero(unsigned current_mxcsr)
    if (util_cpu_caps.has_sse) {
       /* Enable flush to zero mode */
       current_mxcsr |= _MM_FLUSH_ZERO_MASK;
-      if (util_cpu_caps.has_sse3) {
+      if (util_cpu_caps.has_daz) {
          /* Enable denormals are zero mode */
          current_mxcsr |= _MM_DENORMALS_ZERO_MASK;
       }
-- 
1.7.9.5