Replace OS::MemCopy with OS::MemMove (just as fast but more flexible).

src/platform-posix.cc

Index: src/platform-posix.cc
diff --git a/src/platform-posix.cc b/src/platform-posix.cc
index 1b6c1c8352d73350c12ab0d0dcdff70dd40b727b..48898ed9aad0acdb4cc06ccba4b01c9818f26de4 100644
--- a/src/platform-posix.cc
+++ b/src/platform-posix.cc
@@ -322,25 +322,32 @@ int OS::VSNPrintF(Vector<char> str,
 
 
 #if defined(V8_TARGET_ARCH_IA32)
-static OS::MemCopyFunction memcopy_function = NULL;
+static void MemMoveWrapper(void* dest, const void* src, size_t size) {
+  memmove(dest, src, size);
+}
+
+// Initialize to library version so we can call this at any time during startup.
+static OS::MemMoveFunction memmove_function = &MemMoveWrapper;
+
 // Defined in codegen-ia32.cc.
-OS::MemCopyFunction CreateMemCopyFunction();
+OS::MemMoveFunction CreateMemMoveFunction();
 
-// Copy memory area to disjoint memory area.
-void OS::MemCopy(void* dest, const void* src, size_t size) {
+// Copy memory area. No restrictions.
+void OS::MemMove(void* dest, const void* src, size_t size) {
   // Note: here we rely on dependent reads being ordered. This is true
   // on all architectures we currently support.
-  (*memcopy_function)(dest, src, size);
-#ifdef DEBUG
-  CHECK_EQ(0, memcmp(dest, src, size));
-#endif
+  (*memmove_function)(dest, src, size);
 }
+
 #endif  // V8_TARGET_ARCH_IA32
 
 
 void POSIXPostSetUp() {
 #if defined(V8_TARGET_ARCH_IA32)
-  memcopy_function = CreateMemCopyFunction();
+  OS::MemMoveFunction generated_memmove = CreateMemMoveFunction();
+  if (generated_memmove != NULL) {
+    memmove_function = generated_memmove;
+  }
 #endif
   init_fast_sin_function();
   init_fast_cos_function();