Optimize function at its entry instead of at exit.

runtime/vm/stub_code_x64.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/globals.h"
 #if defined(TARGET_ARCH_X64)
 
 #include "vm/assembler.h"
 #include "vm/assembler_macros.h"
 #include "vm/compiler.h"
@@ skipping 1966 matching lines @@
   __ PushObject(Symbols::EqualOperator());  // Target's name.
   __ pushq(RBX);  // ICData
   __ CallRuntime(kUpdateICDataTwoArgsRuntimeEntry);
   __ Drop(4);
   __ LeaveFrame();
 
   __ jmp(&compute_result, Assembler::kNearJump);
 }
 
 // Calls to the runtime to optimize the given function.
-// RDX: function to be reoptimized.
-// RAX: result of function being optimized (preserved).
+// RDI: function to be reoptimized.
+// R10: argument descriptor (preserved).
 void StubCode::GenerateOptimizeFunctionStub(Assembler* assembler) {
+  const Immediate raw_null =
+      Immediate(reinterpret_cast<intptr_t>(Object::null()));
   AssemblerMacros::EnterStubFrame(assembler);
-  __ pushq(RAX);
-  __ pushq(RDX);
+  __ pushq(R10);
+  __ pushq(raw_null);  // Setup space on stack for return value.
+  __ pushq(RDI);
   __ CallRuntime(kOptimizeInvokedFunctionRuntimeEntry);
-  __ popq(RDX);
-  __ popq(RAX);
+  __ popq(RAX);  // Disard argument.
+  __ popq(RAX);  // Get Code object.
+  __ popq(R10);  // Restore argument descriptor.
+  __ movq(RAX, FieldAddress(RAX, Code::instructions_offset()));
+  __ addq(RAX, Immediate(Instructions::HeaderSize() - kHeapObjectTag));
   __ LeaveFrame();
-  __ ret();
+  __ jmp(RAX);
+  __ int3();
 }
 
 
 DECLARE_LEAF_RUNTIME_ENTRY(intptr_t,
                            BigintCompare,
                            RawBigint* left,
                            RawBigint* right);
 
 
 // Does identical check (object references are equal or not equal) with special
@@ skipping 61 matching lines @@
   __ cmpq(left, right);
   __ Bind(&done);
   __ popq(right);
   __ popq(left);
   __ ret();
 }
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_X64