Implement a variation of scalar replacement for non-escaping allocations.

runtime/vm/stub_code_x64.cc

 // Copyright (c) 2013, 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/compiler.h"
 #include "vm/dart_entry.h"
@@ skipping 369 matching lines @@
   __ LeaveFrame();
   __ movq(RBP, RAX);
 
   // Frame is fully rewritten at this point and it is safe to perform a GC.
   // Materialize any objects that were deferred by FillFrame because they
   // require allocation.
   __ EnterStubFrame();
   if (preserve_rax) {
     __ pushq(RBX);  // Preserve result, it will be GC-d here.
   }
-  __ CallRuntime(kDeoptimizeMaterializeDoublesRuntimeEntry);
+  __ pushq(Immediate(Smi::RawValue(0)));  // Space for the result.
+  __ CallRuntime(kDeoptimizeMaterializeRuntimeEntry);
+  // Result tells stub how many bytes to remove from the expression stack
+  // of the bottom-most frame. They were used as materialization arguments.
+  __ popq(RBX);
+  __ SmiUntag(RBX);
   if (preserve_rax) {
     __ popq(RAX);  // Restore result.
   }
   __ LeaveFrame();
 
+  __ popq(RCX);  // Pop return address.
+  __ addq(RSP, RBX);  // Remove materialization arguments.
+  __ pushq(RCX);  // Push return address.
   __ ret();
 }
 
 
 // TOS: return address + call-instruction-size (5 bytes).
 // RAX: result, must be preserved
 void StubCode::GenerateDeoptimizeLazyStub(Assembler* assembler) {
   // Correct return address to point just after the call that is being
   // deoptimized.
   __ popq(RBX);
@@ skipping 1660 matching lines @@
   __ cmpq(left, right);
   __ Bind(&done);
   __ popq(right);
   __ popq(left);
   __ ret();
 }
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_X64