Move deopt reason into PcDescriptor so the EAX/RAX register is not destroyed. Some cleanups in PC d…

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 561 matching lines @@
 //   +------------------+
 //   | 0 as PC marker   | <- TOS
 //   +------------------+
 //   | Saved FP         |
 //   +------------------+
 //   | return-address   |  (deoptimization point)
 //   +------------------+
 //   | optimized frame  |
 //   |  ...             |
 //
-// RAX: Deoptimization reason id.
 void StubCode::GenerateDeoptimizeStub(Assembler* assembler) {
   __ EnterFrame(0);
   // Push registers in their enumeration order: lowest register number at
   // lowest address.
   for (intptr_t i = kNumberOfCpuRegisters - 1; i >= 0; i--) {
     __ pushq(static_cast<Register>(i));
   }
   __ movq(RCX, RSP);  // Saved saved registers block.
   __ ReserveAlignedFrameSpace(0);
   __ SmiUntag(RAX);
-  __ movq(RDI, RAX);  // Set up argument 1 deopt_reason.
-  __ movq(RSI, RCX);  // Set up argument 2 saved_registers_address.
+  __ movq(RDI, RCX);  // Set up argument 1 saved_registers_address.
 
   __ CallRuntime(kDeoptimizeCopyFrameRuntimeEntry);
   // Result (RAX) is stack-size (FP - SP) in bytes, incl. the return address.
   __ LeaveFrame();
   __ popq(RCX);  // Discard return address.
   __ movq(RSP, RBP);
   __ subq(RSP, RAX);
 
   __ EnterFrame(0);
   __ movq(RCX, RSP);  // Get last FP address.
@@ skipping 1329 matching lines @@
 void StubCode::GenerateJumpToErrorHandlerStub(Assembler* assembler) {
   __ movq(RAX, RCX);  // error object.
   __ movq(RBP, RDX);  // target frame_pointer.
   __ movq(RSP, RSI);  // target stack_pointer.
   __ jmp(RDI);  // Jump to the exception handler code.
 }
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_X64