util/bufferiszero: Use i386 host/cpuinfo.h

Use cpuinfo_init() during init_accel(), and the variable cpuinfo
during test_buffer_is_zero_next_accel().  Adjust the logic that
cycles through the set of accelerators for testing.

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

util/bufferiszero.c

@@ -24,6 +24,7 @@
 #include "qemu/osdep.h"
 #include "qemu/cutils.h"
 #include "qemu/bswap.h"
+#include "host/cpuinfo.h"
 
 static bool
 buffer_zero_int(const void *buf, size_t len)
@@ -184,111 +185,75 @@ buffer_zero_avx512(const void *buf, size_t len)
 }
 #endif /* CONFIG_AVX512F_OPT */
 
-
-/* Note that for test_buffer_is_zero_next_accel, the most preferred
- * ISA must have the least significant bit.
- */
-#define CACHE_AVX512F 1
-#define CACHE_AVX2    2
-#define CACHE_SSE4    4
-#define CACHE_SSE2    8
-
-/* Make sure that these variables are appropriately initialized when
+/*
+ * Make sure that these variables are appropriately initialized when
  * SSE2 is enabled on the compiler command-line, but the compiler is
  * too old to support CONFIG_AVX2_OPT.
  */
 #if defined(CONFIG_AVX512F_OPT) || defined(CONFIG_AVX2_OPT)
-# define INIT_CACHE 0
-# define INIT_ACCEL buffer_zero_int
+# define INIT_USED     0
+# define INIT_LENGTH   0
+# define INIT_ACCEL    buffer_zero_int
 #else
 # ifndef __SSE2__
 #  error "ISA selection confusion"
 # endif
-# define INIT_CACHE CACHE_SSE2
-# define INIT_ACCEL buffer_zero_sse2
+# define INIT_USED     CPUINFO_SSE2
+# define INIT_LENGTH   64
+# define INIT_ACCEL    buffer_zero_sse2
 #endif
 
-static unsigned cpuid_cache = INIT_CACHE;
+static unsigned used_accel = INIT_USED;
+static unsigned length_to_accel = INIT_LENGTH;
 static bool (*buffer_accel)(const void *, size_t) = INIT_ACCEL;
-static int length_to_accel = 64;
 
-static void init_accel(unsigned cache)
+static unsigned __attribute__((noinline))
+select_accel_cpuinfo(unsigned info)
 {
-    bool (*fn)(const void *, size_t) = buffer_zero_int;
-    if (cache & CACHE_SSE2) {
-        fn = buffer_zero_sse2;
-        length_to_accel = 64;
-    }
+    /* Array is sorted in order of algorithm preference. */
+    static const struct {
+        unsigned bit;
+        unsigned len;
+        bool (*fn)(const void *, size_t);
+    } all[] = {
+#ifdef CONFIG_AVX512F_OPT
+        { CPUINFO_AVX512F, 256, buffer_zero_avx512 },
+#endif
 #ifdef CONFIG_AVX2_OPT
-    if (cache & CACHE_SSE4) {
-        fn = buffer_zero_sse4;
-        length_to_accel = 64;
-    }
-    if (cache & CACHE_AVX2) {
-        fn = buffer_zero_avx2;
-        length_to_accel = 128;
-    }
+        { CPUINFO_AVX2,    128, buffer_zero_avx2 },
+        { CPUINFO_SSE4,     64, buffer_zero_sse4 },
 #endif
-#ifdef CONFIG_AVX512F_OPT
-    if (cache & CACHE_AVX512F) {
-        fn = buffer_zero_avx512;
-        length_to_accel = 256;
+        { CPUINFO_SSE2,     64, buffer_zero_sse2 },
+        { CPUINFO_ALWAYS,    0, buffer_zero_int },
+    };
+
+    for (unsigned i = 0; i < ARRAY_SIZE(all); ++i) {
+        if (info & all[i].bit) {
+            length_to_accel = all[i].len;
+            buffer_accel = all[i].fn;
+            return all[i].bit;
+        }
     }
-#endif
-    buffer_accel = fn;
+    return 0;
 }
 
 #if defined(CONFIG_AVX512F_OPT) || defined(CONFIG_AVX2_OPT)
-#include "qemu/cpuid.h"
-
-static void __attribute__((constructor)) init_cpuid_cache(void)
+static void __attribute__((constructor)) init_accel(void)
 {
-    unsigned max = __get_cpuid_max(0, NULL);
-    int a, b, c, d;
-    unsigned cache = 0;
-
-    if (max >= 1) {
-        __cpuid(1, a, b, c, d);
-        if (d & bit_SSE2) {
-            cache |= CACHE_SSE2;
-        }
-        if (c & bit_SSE4_1) {
-            cache |= CACHE_SSE4;
-        }
-
-        /* We must check that AVX is not just available, but usable.  */
-        if ((c & bit_OSXSAVE) && (c & bit_AVX) && max >= 7) {
-            unsigned bv = xgetbv_low(0);
-            __cpuid_count(7, 0, a, b, c, d);
-            if ((bv & 0x6) == 0x6 && (b & bit_AVX2)) {
-                cache |= CACHE_AVX2;
-            }
-            /* 0xe6:
-            *  XCR0[7:5] = 111b (OPMASK state, upper 256-bit of ZMM0-ZMM15
-            *                    and ZMM16-ZMM31 state are enabled by OS)
-            *  XCR0[2:1] = 11b (XMM state and YMM state are enabled by OS)
-            */
-            if ((bv & 0xe6) == 0xe6 && (b & bit_AVX512F)) {
-                cache |= CACHE_AVX512F;
-            }
-        }
-    }
-    cpuid_cache = cache;
-    init_accel(cache);
+    used_accel = select_accel_cpuinfo(cpuinfo_init());
 }
 #endif /* CONFIG_AVX2_OPT */
 
 bool test_buffer_is_zero_next_accel(void)
 {
-    /* If no bits set, we just tested buffer_zero_int, and there
-       are no more acceleration options to test.  */
-    if (cpuid_cache == 0) {
-        return false;
-    }
-    /* Disable the accelerator we used before and select a new one.  */
-    cpuid_cache &= cpuid_cache - 1;
-    init_accel(cpuid_cache);
-    return true;
+    /*
+     * Accumulate the accelerators that we've already tested, and
+     * remove them from the set to test this round.  We'll get back
+     * a zero from select_accel_cpuinfo when there are no more.
+     */
+    unsigned used = select_accel_cpuinfo(cpuinfo & ~used_accel);
+    used_accel |= used;
+    return used;
 }
 
 static bool select_accel_fn(const void *buf, size_t len)