Vendor import of compiler-rt trunk r351319 (just before the release_80vendor/compiler-rt/compiler-rt-trunk-r351319vendor/compiler-rt/compiler-rt-release_80-r351543

branch point):
https://llvm.org/svn/llvm-project/compiler-rt/trunk@351319

1 files changed, 12 insertions, 0 deletions

diff --git a/lib/sanitizer_common/sanitizer_libc.cc b/lib/sanitizer_common/sanitizer_libc.cc
index 4b462bfe9728..4032cb10461f 100644
--- a/lib/sanitizer_common/sanitizer_libc.cc
+++ b/lib/sanitizer_common/sanitizer_libc.cc
@@ -73,6 +73,18 @@ void *internal_memmove(void *dest, const void *src, uptr n) {
 }
 
 void *internal_memset(void* s, int c, uptr n) {
+  // Optimize for the most performance-critical case:
+  if ((reinterpret_cast<uptr>(s) % 16) == 0 && (n % 16) == 0) {
+    u64 *p = reinterpret_cast<u64*>(s);
+    u64 *e = p + n / 8;
+    u64 v = c;
+    v |= v << 8;
+    v |= v << 16;
+    v |= v << 32;
+    for (; p < e; p += 2)
+      p[0] = p[1] = v;
+    return s;
+  }
   // The next line prevents Clang from making a call to memset() instead of the
   // loop below.
   // FIXME: building the runtime with -ffreestanding is a better idea. However