Recognize leaf functions: skip stack check and populating the pc slot, store the pc slot lazily in …

runtime/vm/assembler_macros_x64.cc

Index: runtime/vm/assembler_macros_x64.cc
===================================================================
--- runtime/vm/assembler_macros_x64.cc	(revision 9089)
+++ runtime/vm/assembler_macros_x64.cc	(working copy)
@@ -66,6 +66,20 @@
 }
 
 
+void AssemblerMacros::EnterDartLeafFrame(Assembler* assembler,
+                                         intptr_t frame_size) {
+  __ EnterFrame(0);
+  Label dart_entry;
+  // Leave room for the saved PC, it will be filled in lazily, leave
+  // uninitialized.
+  __ subq(RSP, Immediate(frame_size + kWordSize));
+#if defined(DEBUG)
+  // Store an invalid object in saved PC slot.
+  __ movq(Address(RBP, -kWordSize), Immediate(kHeapObjectTag));
+#endif
+}
+
+
 void AssemblerMacros::EnterStubFrame(Assembler* assembler) {
   __ EnterFrame(0);
   __ pushq(Immediate(0));  // Push 0 in the saved PC area for stub frames.