util/bufferiszero: Use __attribute__((target)) for avx2/avx512

Use the attribute, which is supported by clang, instead of
the #pragma, which is not supported and, for some reason,
also not detected by the meson probe, so we fail by -Werror.

Include only <immintrin.h> as that is the outermost "official"
header for these intrinsics -- emmintrin.h and smmintrin -- are
older SSE2 and SSE4 specific headers, while the immintrin.h
includes all of the Intel intrinsics.

Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

2 files changed, 8 insertions, 41 deletions

diff --git a/meson.build b/meson.build
index 6d212f6..58d8cd6 100644
--- a/meson.build
+++ b/meson.build
@@ -2338,11 +2338,9 @@ config_host_data.set('CONFIG_CPUID_H', have_cpuid_h)
 config_host_data.set('CONFIG_AVX2_OPT', get_option('avx2') \
   .require(have_cpuid_h, error_message: 'cpuid.h not available, cannot enable AVX2') \
   .require(cc.links('''
-    #pragma GCC push_options
-    #pragma GCC target("avx2")
     #include <cpuid.h>
     #include <immintrin.h>
-    static int bar(void *a) {
+    static int __attribute__((target("avx2"))) bar(void *a) {
       __m256i x = *(__m256i *)a;
       return _mm256_testz_si256(x, x);
     }
@@ -2352,11 +2350,9 @@ config_host_data.set('CONFIG_AVX2_OPT', get_option('avx2') \
 config_host_data.set('CONFIG_AVX512F_OPT', get_option('avx512f') \
   .require(have_cpuid_h, error_message: 'cpuid.h not available, cannot enable AVX512F') \
   .require(cc.links('''
-    #pragma GCC push_options
-    #pragma GCC target("avx512f")
     #include <cpuid.h>
     #include <immintrin.h>
-    static int bar(void *a) {
+    static int __attribute__((target("avx512f"))) bar(void *a) {
       __m512i x = *(__m512i *)a;
       return _mm512_test_epi64_mask(x, x);
     }
diff --git a/util/bufferiszero.c b/util/bufferiszero.c
index ec3cd4c..1790ded 100644
--- a/util/bufferiszero.c
+++ b/util/bufferiszero.c
@@ -64,18 +64,11 @@ buffer_zero_int(const void *buf, size_t len)
 }
 
 #if defined(CONFIG_AVX512F_OPT) || defined(CONFIG_AVX2_OPT) || defined(__SSE2__)
-/* Do not use push_options pragmas unnecessarily, because clang
- * does not support them.
- */
-#if defined(CONFIG_AVX512F_OPT) || defined(CONFIG_AVX2_OPT)
-#pragma GCC push_options
-#pragma GCC target("sse2")
-#endif
-#include <emmintrin.h>
+#include <immintrin.h>
 
 /* Note that each of these vectorized functions require len >= 64.  */
 
-static bool
+static bool __attribute__((target("sse2")))
 buffer_zero_sse2(const void *buf, size_t len)
 {
     __m128i t = _mm_loadu_si128(buf);
@@ -104,20 +97,9 @@ buffer_zero_sse2(const void *buf, size_t len)
 
     return _mm_movemask_epi8(_mm_cmpeq_epi8(t, zero)) == 0xFFFF;
 }
-#if defined(CONFIG_AVX512F_OPT) || defined(CONFIG_AVX2_OPT)
-#pragma GCC pop_options
-#endif
 
 #ifdef CONFIG_AVX2_OPT
-/* Note that due to restrictions/bugs wrt __builtin functions in gcc <= 4.8,
- * the includes have to be within the corresponding push_options region, and
- * therefore the regions themselves have to be ordered with increasing ISA.
- */
-#pragma GCC push_options
-#pragma GCC target("sse4")
-#include <smmintrin.h>
-
-static bool
+static bool __attribute__((target("sse4")))
 buffer_zero_sse4(const void *buf, size_t len)
 {
     __m128i t = _mm_loadu_si128(buf);
@@ -145,12 +127,7 @@ buffer_zero_sse4(const void *buf, size_t len)
     return _mm_testz_si128(t, t);
 }
 
-#pragma GCC pop_options
-#pragma GCC push_options
-#pragma GCC target("avx2")
-#include <immintrin.h>
-
-static bool
+static bool __attribute__((target("avx2")))
 buffer_zero_avx2(const void *buf, size_t len)
 {
     /* Begin with an unaligned head of 32 bytes.  */
@@ -176,15 +153,10 @@ buffer_zero_avx2(const void *buf, size_t len)
 
     return _mm256_testz_si256(t, t);
 }
-#pragma GCC pop_options
 #endif /* CONFIG_AVX2_OPT */
 
 #ifdef CONFIG_AVX512F_OPT
-#pragma GCC push_options
-#pragma GCC target("avx512f")
-#include <immintrin.h>
-
-static bool
+static bool __attribute__((target("avx512f")))
 buffer_zero_avx512(const void *buf, size_t len)
 {
     /* Begin with an unaligned head of 64 bytes.  */
@@ -210,8 +182,7 @@ buffer_zero_avx512(const void *buf, size_t len)
     return !_mm512_test_epi64_mask(t, t);
 
 }
-#pragma GCC pop_options
-#endif
+#endif /* CONFIG_AVX512F_OPT */
 
 
 /* Note that for test_buffer_is_zero_next_accel, the most preferred