avx2 configure: Use primitives in test

Use the avx2 primitives during the test, thus making sure that the
compiler and assembler could actually use avx2.

This also detects the failure case on gcc 4.8.x with -save-temps
and avoids the need for the gcc version check in cutils.
Signed-off-by: NDr. David Alan Gilbert <dgilbert@redhat.com>
Message-Id: <1465557378-24105-3-git-send-email-dgilbert@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

configure

@@ -1779,13 +1779,20 @@ fi
 # avx2 optimization requirement check
 
 cat > $TMPC << EOF
-static void bar(void) {}
+#pragma GCC push_options
+#pragma GCC target("avx2")
+#include <cpuid.h>
+#include <immintrin.h>
+
+static int bar(void *a) {
+    return _mm256_movemask_epi8(_mm256_cmpeq_epi8(*(__m256i *)a, (__m256i){0}));
+}
 static void *bar_ifunc(void) {return (void*) bar;}
-void foo(void) __attribute__((ifunc("bar_ifunc")));
-int main(void) { foo(); return 0; }
+int foo(void *a) __attribute__((ifunc("bar_ifunc")));
+int main(int argc, char *argv[]) { return foo(argv[0]);}
 EOF
-if compile_prog "-mavx2" "" ; then
-    if readelf --syms $TMPE |grep "IFUNC.*foo" >/dev/null 2>&1; then
+if compile_object "" ; then
+    if readelf --syms $TMPO |grep "IFUNC.*foo" >/dev/null 2>&1; then
         avx2_opt="yes"
     fi
 fi

util/cutils.c

@@ -256,13 +256,7 @@ static size_t buffer_find_nonzero_offset_inner(const void *buf, size_t len)
     return i * sizeof(VECTYPE);
 }
 
-/*
- * GCC before version 4.9 has a bug which will cause the target
- * attribute work incorrectly and failed to compile in some case,
- * restrict the gcc version to 4.9+ to prevent the failure.
- */
-
-#if defined CONFIG_AVX2_OPT && QEMU_GNUC_PREREQ(4, 9)
+#if defined CONFIG_AVX2_OPT
 #pragma GCC push_options
 #pragma GCC target("avx2")
 #include <cpuid.h>