Disconnects code objects from infrequently used unoptimized functions.

runtime/vm/flow_graph_compiler_x64.cc

Index: runtime/vm/flow_graph_compiler_x64.cc
===================================================================
--- runtime/vm/flow_graph_compiler_x64.cc	(revision 28803)
+++ runtime/vm/flow_graph_compiler_x64.cc	(working copy)
@@ -8,6 +8,7 @@
 #include "vm/flow_graph_compiler.h"
 
 #include "vm/ast_printer.h"
+#include "vm/compiler.h"
 #include "vm/dart_entry.h"
 #include "vm/deopt_instructions.h"
 #include "vm/il_printer.h"
@@ -1131,6 +1132,29 @@
     ASSERT(StackSize() >= 0);
     __ EnterDartFrameWithInfo(StackSize() * kWordSize, new_pp, new_pc);
   }
+
+  // TODO(zra): maybe do this only before we try to optimize?
+  if (FLAG_collect_code) {
+    // If we are collecting code, make sure this function still has a pointer
+    // to the code object.
+    // TODO(zra): Is it cheaper just to write the Function fields with the
+    // code object without doing the test?
+    Label is_connected;
+    const Register function_reg = RDI;
+    __ LoadObject(function_reg, function, PP);
+    __ movq(RAX, FieldAddress(function_reg, Function::code_offset()));
+    __ CompareObject(RAX, Object::null_object(), PP);
+    __ j(NOT_EQUAL, &is_connected, Assembler::kNearJump);
+    __ movq(RAX, Address(RBP, kPcMarkerSlotFromFp * kWordSize));
+    const intptr_t code_pc_dist =
+      Instructions::HeaderSize() - Instructions::code_offset() +
+      Assembler::kEntryPointToPcMarkerOffset;
+    __ movq(RAX, Address(RAX, -code_pc_dist));
+    __ movq(FieldAddress(function_reg, Function::code_offset()), RAX);
+    __ movl(
+        FieldAddress(function_reg, Function::unoptimized_code_offset()), RAX);
+    __ Bind(&is_connected);
+  }
 }
 
 
@@ -1447,8 +1471,27 @@
   // illegal class id was found, the target is a cache miss handler that can
   // be invoked as a normal Dart function.
   __ movq(RAX, FieldAddress(RDI, RCX, TIMES_8, base + kWordSize));
-  __ movq(RAX, FieldAddress(RAX, Function::code_offset()));
-  __ movq(RAX, FieldAddress(RAX, Code::instructions_offset()));
+  __ movq(RBX, FieldAddress(RAX, Function::code_offset()));
+  if (FLAG_collect_code) {
+    // If we are collecting code, the code object may be null.
+    Label is_compiled;
+    const Immediate& raw_null =
+        Immediate(reinterpret_cast<intptr_t>(Object::null()));
+    __ cmpq(RBX, raw_null);
+    __ j(NOT_EQUAL, &is_compiled, Assembler::kNearJump);
+    __ EnterStubFrame();
+    __ pushq(RDX);  // Preserve arguments descriptor array.
+    __ pushq(RCX);  // Preserve IC data object.
+    __ pushq(RAX);  // Pass function.
+    __ CallRuntime(kCompileFunctionRuntimeEntry, 1);
+    __ popq(RAX);  // Restore function.
+    __ popq(RCX);  // Restore IC data array.
+    __ popq(RDX);  // Restore arguments descriptor array.
+    __ LeaveFrame();
+    __ movq(RBX, FieldAddress(RAX, Function::code_offset()));
+    __ Bind(&is_compiled);
+  }
+  __ movq(RAX, FieldAddress(RBX, Code::instructions_offset()));
   __ LoadObject(RBX, ic_data, PP);
   __ LoadObject(R10, arguments_descriptor, PP);
   __ AddImmediate(