Merge tag 'pull-misc-20240503' of https://gitlab.com/rth7680/qemu into staging

util/bufferiszero:
  - Remove sse4.1 and avx512 variants
  - Reorganize for early test for acceleration
  - Remove useless prefetches
  - Optimize sse2, avx2 and integer variants
  - Add simd acceleration for aarch64
  - Add bufferiszero-bench

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* tag 'pull-misc-20240503' of https://gitlab.com/rth7680/qemu:
  tests/bench: Add bufferiszero-bench
  util/bufferiszero: Add simd acceleration for aarch64
  util/bufferiszero: Simplify test_buffer_is_zero_next_accel
  util/bufferiszero: Introduce biz_accel_fn typedef
  util/bufferiszero: Improve scalar variant
  util/bufferiszero: Optimize SSE2 and AVX2 variants
  util/bufferiszero: Remove useless prefetches
  util/bufferiszero: Reorganize for early test for acceleration
  util/bufferiszero: Remove AVX512 variant
  util/bufferiszero: Remove SSE4.1 variant

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

1 files changed, 31 insertions, 1 deletions

diff --git a/include/qemu/cutils.h b/include/qemu/cutils.h
index 92c927a..741dade 100644
--- a/include/qemu/cutils.h
+++ b/include/qemu/cutils.h
@@ -187,9 +187,39 @@ char *freq_to_str(uint64_t freq_hz);
 /* used to print char* safely */
 #define STR_OR_NULL(str) ((str) ? (str) : "null")
 
-bool buffer_is_zero(const void *buf, size_t len);
+/*
+ * Check if a buffer is all zeroes.
+ */
+
+bool buffer_is_zero_ool(const void *vbuf, size_t len);
+bool buffer_is_zero_ge256(const void *vbuf, size_t len);
 bool test_buffer_is_zero_next_accel(void);
 
+static inline bool buffer_is_zero_sample3(const char *buf, size_t len)
+{
+    /*
+     * For any reasonably sized buffer, these three samples come from
+     * three different cachelines.  In qemu-img usage, we find that
+     * each byte eliminates more than half of all buffer testing.
+     * It is therefore critical to performance that the byte tests
+     * short-circuit, so that we do not pull in additional cache lines.
+     * Do not "optimize" this to !(a | b | c).
+     */
+    return !buf[0] && !buf[len - 1] && !buf[len / 2];
+}
+
+#ifdef __OPTIMIZE__
+static inline bool buffer_is_zero(const void *buf, size_t len)
+{
+    return (__builtin_constant_p(len) && len >= 256
+            ? buffer_is_zero_sample3(buf, len) &&
+              buffer_is_zero_ge256(buf, len)
+            : buffer_is_zero_ool(buf, len));
+}
+#else
+#define buffer_is_zero  buffer_is_zero_ool
+#endif
+
 /*
  * Implementation of ULEB128 (http://en.wikipedia.org/wiki/LEB128)
  * Input is limited to 14-bit numbers