Improve code (less code, slightly faster) for polymorphic calls, by loading the argument descriptor…

runtime/vm/code_patcher_ia32.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"  // Needed here to get TARGET_ARCH_IA32.
 #if defined(TARGET_ARCH_IA32)
 
 #include "vm/assembler.h"
 #include "vm/code_patcher.h"
 #include "vm/cpu.h"
@@ skipping 75 matching lines @@
 
   RawObject* ic_data() const { return immediate_one(); }
   RawObject* arguments_descriptor() const { return immediate_two(); }
 
  private:
   DISALLOW_IMPLICIT_CONSTRUCTORS(InstanceCall);
 };
 
 
 // The expected pattern of a dart static call:
-//  mov EDX, arguments_descriptor_array
+//  mov EDX, arguments_descriptor_array (optional in polymorphic calls)
 //  call target_address
 //  <- return address
 class StaticCall : public ValueObject {
  public:
   explicit StaticCall(uword return_address)
       : start_(return_address - (kNumInstructions * kInstructionSize)) {
     ASSERT(IsValid(return_address));
     ASSERT(kInstructionSize == Assembler::kCallExternalLabelSize);
   }
 
   static bool IsValid(uword return_address) {
     uint8_t* code_bytes =
         reinterpret_cast<uint8_t*>(
             return_address - (kNumInstructions * kInstructionSize));
-    return (code_bytes[0] == 0xBA) &&
-           (code_bytes[1 * kInstructionSize] == 0xE8);
+    return (code_bytes[0] == 0xE8);
   }
 
   uword target() const {
     const uword offset = *reinterpret_cast<uword*>(call_address() + 1);
     return return_address() + offset;
   }
 
   void set_target(uword target) const {
     uword* target_addr = reinterpret_cast<uword*>(call_address() + 1);
     uword offset = target - return_address();
     *target_addr = offset;
     CPU::FlushICache(call_address(), kInstructionSize);
   }
 
-  static const int kNumInstructions = 2;
+  static const int kNumInstructions = 1;
   static const int kInstructionSize = 5;  // All instructions have same length.
 
  private:
   uword return_address() const {
     return start_ + kNumInstructions * kInstructionSize;
   }
 
   uword call_address() const {
-    return start_ + 1 * kInstructionSize;
+    return start_;
   }
 
   uword start_;
 
   DISALLOW_IMPLICIT_CONSTRUCTORS(StaticCall);
 };
 
 
 uword CodePatcher::GetStaticCallTargetAt(uword return_address,
                                          const Code& code) {
@@ skipping 46 matching lines @@
 }
 
 
 intptr_t CodePatcher::InstanceCallSizeInBytes() {
   return DartCallPattern::kNumInstructions * DartCallPattern::kInstructionSize;
 }
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_IA32