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

runtime/vm/stub_code_ia32.cc

 // Copyright (c) 2011, 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_IA32)
 
 #include "vm/assembler.h"
 #include "vm/assembler_macros.h"
 #include "vm/compiler.h"
@@ skipping 568 matching lines @@
 //   +------------------+
 //   | 0 as PC marker   | <- TOS
 //   +------------------+
 //   | Saved FP         |
 //   +------------------+
 //   | return-address   |  (deoptimization point)
 //   +------------------+
 //   | optimized frame  |
 //   |  ...             |
 //
-// EAX: 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--) {
     __ pushl(static_cast<Register>(i));
   }
   __ movl(ECX, ESP);  // Saved saved registers block.
-  __ ReserveAlignedFrameSpace(2 * kWordSize);
+  __ ReserveAlignedFrameSpace(1 * kWordSize);
   __ SmiUntag(EAX);
-  __ movl(Address(ESP, 0), EAX);  // Deopt reason (untagged).
-  __ movl(Address(ESP, kWordSize), ECX);  // Start of register block.
+  __ movl(Address(ESP, 0), ECX);  // Start of register block.
   __ CallRuntime(kDeoptimizeCopyFrameRuntimeEntry);
   // Result (EAX) is stack-size (FP - SP) in bytes, incl. the return address.
   __ LeaveFrame();
   __ popl(EDX);  // Discard return address.
   __ movl(ESP, EBP);
   __ subl(ESP, EAX);
 
   __ EnterFrame(0);
   __ movl(ECX, ESP);  // Get last FP address.
   __ ReserveAlignedFrameSpace(1 * kWordSize);
@@ skipping 1362 matching lines @@
   __ movl(EAX, Address(ESP, 4 * kWordSize));  // Load error object.
   __ movl(EBP, Address(ESP, 3 * kWordSize));  // Load target frame_pointer.
   __ movl(EBX, Address(ESP, 1 * kWordSize));  // Load target PC into EBX.
   __ movl(ESP, Address(ESP, 2 * kWordSize));  // Load target stack_pointer.
   __ jmp(EBX);  // Jump to the exception handler code.
 }
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_IA32