Define missing SNAPPY_PREFETCH macros.

PiperOrigin-RevId: 523287305

CMakeLists.txt

diff --git a/CMakeLists.txt b/CMakeLists.txt
index c3062e2..7711693 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -154,6 +154,12 @@
 }" HAVE_BUILTIN_CTZ)
 
 check_cxx_source_compiles("
+int main() {
+  __builtin_prefetch(0, 0, 3);
+  return 0;
+}" HAVE_BUILTIN_PREFETCH)
+
+check_cxx_source_compiles("
 __attribute__((always_inline)) int zero() { return 0; }
 
 int main() {

cmake/config.h.in

diff --git a/cmake/config.h.in b/cmake/config.h.in
index d1de25c..3510c27 100644
--- a/cmake/config.h.in
+++ b/cmake/config.h.in
@@ -10,6 +10,9 @@
 /* Define to 1 if the compiler supports __builtin_expect. */
 #cmakedefine01 HAVE_BUILTIN_EXPECT
 
+/* Define to 1 if the compiler supports __builtin_prefetch. */
+#cmakedefine01 HAVE_BUILTIN_PREFETCH
+
 /* Define to 1 if you have a definition for mmap() in <sys/mman.h>. */
 #cmakedefine01 HAVE_FUNC_MMAP
 

snappy-stubs-internal.h

diff --git a/snappy-stubs-internal.h b/snappy-stubs-internal.h
index 1548ed7..526c38b 100644
--- a/snappy-stubs-internal.h
+++ b/snappy-stubs-internal.h
@@ -105,6 +105,12 @@
 #define SNAPPY_ATTRIBUTE_ALWAYS_INLINE
 #endif  // HAVE_ATTRIBUTE_ALWAYS_INLINE
 
+#if HAVE_BUILTIN_PREFETCH
+#define SNAPPY_PREFETCH(ptr) __builtin_prefetch(ptr, 0, 3)
+#else
+#define SNAPPY_PREFETCH(ptr) (void)(ptr)
+#endif
+
 // Stubbed version of ABSL_FLAG.
 //
 // In the open source version, flags can only be changed at compile time.