Pattern match on generated code to find edge counters.

runtime/vm/code_patcher_mips.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_MIPS.
 #if defined(TARGET_ARCH_MIPS)
 
 #include "vm/code_patcher.h"
 
 #include "vm/instructions.h"
@@ skipping 66 matching lines @@
   ASSERT(code.ContainsInstructionAt(return_address));
   CallPattern static_call(return_address, code);
   ICData& ic_data = ICData::Handle();
   ic_data ^= static_call.IcData();
   if (ic_data_result != NULL) {
     *ic_data_result = ic_data.raw();
   }
   return ic_data.GetTargetAt(0);
 }
 
+
+// The expected code pattern of an edge counter in unoptimized code:
+//     lw t0, imm(pp)
+class EdgeCounter : public ValueObject {
+ public:
+  EdgeCounter(uword start, const Code& code)
+      : start_(start), object_pool_(Array::Handle(code.ObjectPool())) {
+    ASSERT(IsValid(start));
+  }
+
+  static bool IsValid(uword start) {
+    Instr* instr = Instr::At(start);
+    return (instr->OpcodeField() == LW)
+        && (instr->RtField() == T0)
+        && (instr->RsField() == PP);
+  }
+
+  RawObject* edge_counter() const {
+    return object_pool_.At(IndexFromPPLoad(start_));
+  }
+
+ private:
+  static intptr_t IndexFromPPLoad(uword start) {
+    ASSERT(IsValid(start));
+    int offset = Instr::At(start)->SImmField() + kHeapObjectTag;

[Florian Schneider, 2013/09/30 08:55:38]

What about indices in the constant pool greater than the maximum immediate size
(kImmbits=16)?

I think the assember will emit a multiple instruction (like on ARM) in that
case.

+    return (offset - Array::data_offset()) / kWordSize;
+  }
+
+  uword start_;
+  const Array& object_pool_;
+};
+
+
+RawObject* CodePatcher::GetEdgeCounterAt(uword pc, const Code& code) {
+  ASSERT(code.ContainsInstructionAt(pc));
+  EdgeCounter counter(pc, code);
+  return counter.edge_counter();
+}
+
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_MIPS