Write barrier audit: Verify previous value in generated code.

runtime/vm/flow_graph_compiler_ia32.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"  // Needed here to get TARGET_ARCH_IA32.
 #if defined(TARGET_ARCH_IA32)
 
 #include "vm/flow_graph_compiler.h"
 
 #include "vm/ast_printer.h"
@@ skipping 1222 matching lines @@
 #if defined(DEBUG)
   intptr_t increment_start = assembler_->CodeSize();
 #endif  // DEBUG
   __ IncrementSmiField(FieldAddress(EAX, Array::element_offset(0)), 1);
   DEBUG_ASSERT((assembler_->CodeSize() - increment_start) ==
                EdgeCounterIncrementSizeInBytes());
 }
 
 
 int32_t FlowGraphCompiler::EdgeCounterIncrementSizeInBytes() {
-  return VerifiedMemory::enabled() ? 16 : 4;
+  return VerifiedMemory::enabled() ? 50 : 4;

[Ivan Posva, 2014/11/14 22:09:11]

This looks like an arbitrary number. How does one know to update this if the
number of instructions or the encoding changes?

[koda, 2014/11/17 16:17:11]

In debug mode, the ASSERT above will fail immediately (and in release mode,
CodePatcher will very likely crash).

Added more explicit instructions, and an explanation why the number must be
constant across all code in an isolate (due to its use by CodePatcher).

 }
 
 
 void FlowGraphCompiler::EmitOptimizedInstanceCall(
     ExternalLabel* target_label,
     const ICData& ic_data,
     intptr_t argument_count,
     intptr_t deopt_id,
     intptr_t token_pos,
     LocationSummary* locs) {
@@ skipping 560 matching lines @@
   __ movups(reg, Address(ESP, 0));
   __ addl(ESP, Immediate(kFpuRegisterSize));
 }
 
 
 #undef __
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_IA32