Index: compiler-rt/lib/sanitizer_common/sanitizer_common_interceptors.inc
===================================================================
--- compiler-rt/lib/sanitizer_common/sanitizer_common_interceptors.inc
+++ compiler-rt/lib/sanitizer_common/sanitizer_common_interceptors.inc
@@ -876,6 +876,51 @@
 #define INIT_MEMSET
 #endif
 
+#if SANITIZER_INTERCEPT_MEMSET_PATTERN
+INTERCEPTOR(void, memset_pattern4, void *s, const void *p, SIZE_T n) {
+  void *ctx;
+  if (COMMON_INTERCEPTOR_NOTHING_IS_INITIALIZED) {
+    internal_memset_pattern4(s, p, n);
+    return;
+  }
+  COMMON_INTERCEPTOR_ENTER(ctx, memset_pattern4, s, p, n);
+  if (common_flags()->intercept_intrin)
+    COMMON_INTERCEPTOR_WRITE_RANGE(ctx, s, n);
+  REAL(memset_pattern4)(s, p, n);
+}
+
+INTERCEPTOR(void, memset_pattern8, void *s, const void *p, SIZE_T n) {
+  void *ctx;
+  if (COMMON_INTERCEPTOR_NOTHING_IS_INITIALIZED) {
+    internal_memset_pattern8(s, p, n);
+    return;
+  }
+  COMMON_INTERCEPTOR_ENTER(ctx, memset_pattern8, s, p, n);
+  if (common_flags()->intercept_intrin)
+    COMMON_INTERCEPTOR_WRITE_RANGE(ctx, s, n);
+  REAL(memset_pattern8)(s, p, n);
+}
+
+INTERCEPTOR(void, memset_pattern16, void *s, const void *p, SIZE_T n) {
+  void *ctx;
+  if (COMMON_INTERCEPTOR_NOTHING_IS_INITIALIZED) {
+    internal_memset_pattern16(s, p, n);
+    return;
+  }
+  COMMON_INTERCEPTOR_ENTER(ctx, memset_pattern16, s, p, n);
+  if (common_flags()->intercept_intrin)
+    COMMON_INTERCEPTOR_WRITE_RANGE(ctx, s, n);
+  REAL(memset_pattern16)(s, p, n);
+}
+
+#define INIT_MEMSET_PATTERN \
+  COMMON_INTERCEPT_FUNCTION(memset_pattern4) \
+  COMMON_INTERCEPT_FUNCTION(memset_pattern8) \
+  COMMON_INTERCEPT_FUNCTION(memset_pattern16)
+#else
+#define INIT_MEMSET_PATTERN
+#endif
+
 #if SANITIZER_INTERCEPT_MEMMOVE
 INTERCEPTOR(void *, memmove, void *dst, const void *src, uptr size) {
   void *ctx;
@@ -10491,6 +10536,7 @@
   INIT_MEMMOVE;
   INIT_MEMCPY;
   INIT_MEMCHR;
+  INIT_MEMSET_PATTERN;
   INIT_MEMCMP;
   INIT_BCMP;
   INIT_MEMRCHR;
Index: compiler-rt/lib/sanitizer_common/sanitizer_libc.h
===================================================================
--- compiler-rt/lib/sanitizer_common/sanitizer_libc.h
+++ compiler-rt/lib/sanitizer_common/sanitizer_libc.h
@@ -33,6 +33,9 @@
 void *internal_memmove(void *dest, const void *src, uptr n);
 // Should not be used in performance-critical places.
 void *internal_memset(void *s, int c, uptr n);
+void internal_memset_pattern4(void *s, const void *p, uptr n);
+void internal_memset_pattern8(void *s, const void *p, uptr n);
+void internal_memset_pattern16(void *s, const void *p, uptr n);
 char* internal_strchr(const char *s, int c);
 char *internal_strchrnul(const char *s, int c);
 int internal_strcmp(const char *s1, const char *s2);
Index: compiler-rt/lib/sanitizer_common/sanitizer_libc.cpp
===================================================================
--- compiler-rt/lib/sanitizer_common/sanitizer_libc.cpp
+++ compiler-rt/lib/sanitizer_common/sanitizer_libc.cpp
@@ -96,6 +96,35 @@
   return s;
 }
 
+// using internal_memmove, thus
+// using those in slow code paths
+template<int chunk>
+static void internal_memset_pattern(void *src, const void *pattern, uptr n) {
+  char *s = (char*)src;
+  char *end = s + n;
+  char *o = s;
+
+  while (end - o >= chunk) {
+    internal_memmove(o, pattern, chunk);
+    o += chunk;
+  }
+
+  if (end - o != 0)
+    internal_memmove(o, pattern, end - o);
+}
+
+void internal_memset_pattern4(void *s, const void *pattern, uptr n) {
+  internal_memset_pattern<4>(s, pattern, n);
+}
+
+void internal_memset_pattern8(void *s, const void *pattern, uptr n) {
+  internal_memset_pattern<8>(s, pattern, n);
+}
+
+void internal_memset_pattern16(void *s, const void *pattern, uptr n) {
+  internal_memset_pattern<16>(s, pattern, n);
+}
+
 uptr internal_strcspn(const char *s, const char *reject) {
   uptr i;
   for (i = 0; s[i]; i++) {
Index: compiler-rt/lib/sanitizer_common/sanitizer_platform_interceptors.h
===================================================================
--- compiler-rt/lib/sanitizer_common/sanitizer_platform_interceptors.h
+++ compiler-rt/lib/sanitizer_common/sanitizer_platform_interceptors.h
@@ -158,6 +158,7 @@
 #define SANITIZER_INTERCEPT_BCMP \
   SANITIZER_INTERCEPT_MEMCMP &&  \
       ((SI_POSIX && _GNU_SOURCE) || SI_NETBSD || SI_FREEBSD)
+#define SANITIZER_INTERCEPT_MEMSET_PATTERN SI_MAC
 #define SANITIZER_INTERCEPT_STRNDUP SI_POSIX
 #define SANITIZER_INTERCEPT___STRNDUP SI_GLIBC
 #if defined(__ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__) && \
Index: compiler-rt/test/sanitizer_common/TestCases/Darwin/memset_pattern.cpp
===================================================================
--- /dev/null
+++ compiler-rt/test/sanitizer_common/TestCases/Darwin/memset_pattern.cpp
@@ -0,0 +1,18 @@
+// RUN: %clangxx -g %s -o %t
+#include <stdlib.h>
+#include <string.h>
+
+int main(void) {
+  char s[16];
+  memset_pattern4(s, "abc", sizeof(s));
+
+  printf("%s\n", s);
+  memset_pattern4(s, "abcd", sizeof(s));
+  s[15] = 0;
+  printf("%s\n", s);
+// CHECK: abc
+// CHECK: abcdabcdabcdabcd
+  return 0;
+}
+
+