Reapply "Initial implementation of on-stack replacement (OSR)."

runtime/vm/assembler_x64.cc

Index: runtime/vm/assembler_x64.cc
diff --git a/runtime/vm/assembler_x64.cc b/runtime/vm/assembler_x64.cc
index 238574920f2dab52fc0116bf904812c7ebdd5dfc..c1d90dbb034c781a6dc39e3329833a2d5f16e1c5 100644
--- a/runtime/vm/assembler_x64.cc
+++ b/runtime/vm/assembler_x64.cc
@@ -9,6 +9,7 @@
 #include "vm/heap.h"
 #include "vm/memory_region.h"
 #include "vm/runtime_entry.h"
+#include "vm/stack_frame.h"
 #include "vm/stub_code.h"
 
 namespace dart {
@@ -2279,15 +2280,16 @@ void Assembler::CallRuntime(const RuntimeEntry& entry) {
 
 
 void Assembler::EnterDartFrame(intptr_t frame_size) {
-  const intptr_t offset = CodeSize();
   EnterFrame(0);
   Label dart_entry;
   call(&dart_entry);
   Bind(&dart_entry);
-  // Adjust saved PC for any intrinsic code that could have been generated
-  // before a frame is created.
+  // The runtime system assumes that the code marker address is
+  // kEntryPointToPcMarkerOffset bytes from the entry.  If there is any code
+  // generated before entering the frame, the address needs to be adjusted.
+  const intptr_t offset = kEntryPointToPcMarkerOffset - CodeSize();
   if (offset != 0) {
-    addq(Address(RSP, 0), Immediate(-offset));
+    addq(Address(RSP, 0), Immediate(offset));
   }
   if (frame_size != 0) {
     subq(RSP, Immediate(frame_size));
@@ -2295,6 +2297,29 @@ void Assembler::EnterDartFrame(intptr_t frame_size) {
 }
 
 
+// On entry to a function compiled for OSR, the caller's frame pointer, the
+// stack locals, and any copied parameters are already in place.  The frame
+// pointer is already set up.  The PC marker is not correct for the
+// optimized function and there may be extra space for spill slots to
+// allocate.
+void Assembler::EnterOsrFrame(intptr_t extra_size) {
+  Label dart_entry;
+  call(&dart_entry);
+  Bind(&dart_entry);
+  // The runtime system assumes that the code marker address is
+  // kEntryPointToPcMarkerOffset bytes from the entry.  Since there is no
+  // code to set up the frame pointer, the address needs to be adjusted.
+  const intptr_t offset = kEntryPointToPcMarkerOffset - CodeSize();
+  if (offset != 0) {
+    addq(Address(RSP, 0), Immediate(offset));
+  }
+  popq(Address(RBP, kPcMarkerSlotFromFp * kWordSize));
+  if (extra_size != 0) {
+    subq(RSP, Immediate(extra_size));
+  }
+}
+
+
 void Assembler::EnterStubFrame() {
   EnterFrame(0);
   pushq(Immediate(0));  // Push 0 in the saved PC area for stub frames.