Debugger: correctly redirect code with no stack check.

src/debug.cc

Index: src/debug.cc
diff --git a/src/debug.cc b/src/debug.cc
index e6365289fdec37e10afa0496054d73099dcaae9a..38d9f47f29d186a41e6d4d225fb1fd2369e6a4f6 100644
--- a/src/debug.cc
+++ b/src/debug.cc
@@ -1311,13 +1311,10 @@ void Debug::ClearStepNext() {
 }
 
 
-// We start counting call sites from the stack check because the declaration
-// code at the start of the function may have changed on recompile.
-static void SkipToStackCheck(Isolate* isolate, RelocIterator* it) {
-  while (Code::GetCodeFromTargetAddress(it->rinfo()->target_address()) !=
-         *isolate->builtins()->StackCheck()) {
-    it->next();
-  }
+bool MatchingCodeTargets(Code* target1, Code* target2) {
+  if (target1 == target2) return true;
+  if (target1->kind() != target2->kind()) return false;
+  return target1->is_handler() || target1->is_inline_cache_stub();
 }
 
 
@@ -1328,24 +1325,42 @@ static Address ComputeNewPcForRedirect(Code* new_code, Code* old_code,
   DCHECK_EQ(old_code->kind(), Code::FUNCTION);
   DCHECK_EQ(new_code->kind(), Code::FUNCTION);
   DCHECK(new_code->has_debug_break_slots());
-  int mask = RelocInfo::kCodeTargetMask;
-  int index = 0;
+  static const int mask = RelocInfo::kCodeTargetMask;
+
+  // Find the target of the current call.
+  Code* target = NULL;
   intptr_t delta = 0;
-  Isolate* isolate = new_code->GetIsolate();
-  RelocIterator old_it(old_code, mask);
-  for (SkipToStackCheck(isolate, &old_it); !old_it.done(); old_it.next()) {
-    RelocInfo* rinfo = old_it.rinfo();
+  for (RelocIterator it(old_code, mask); !it.done(); it.next()) {
+    RelocInfo* rinfo = it.rinfo();
     Address current_pc = rinfo->pc();
     // The frame PC is behind the call instruction by the call instruction size.
     if (current_pc > old_pc) break;
-    index++;
     delta = old_pc - current_pc;
+    target = Code::GetCodeFromTargetAddress(rinfo->target_address());
+  }
+
+  // Count the number of calls to the same target before the current call.
+  int index = 0;
+  for (RelocIterator it(old_code, mask); !it.done(); it.next()) {
+    RelocInfo* rinfo = it.rinfo();
+    Address current_pc = rinfo->pc();
+    if (current_pc > old_pc) break;
+    Code* current = Code::GetCodeFromTargetAddress(rinfo->target_address());
+    if (MatchingCodeTargets(target, current)) index++;
+  }
+
+  DCHECK(index > 0);
+
+  // Repeat the count on the new code to find corresponding call.
+  for (RelocIterator it(new_code, mask); !it.done(); it.next()) {
+    RelocInfo* rinfo = it.rinfo();
+    Code* current = Code::GetCodeFromTargetAddress(rinfo->target_address());
+    if (MatchingCodeTargets(target, current)) index--;
+    if (index == 0) return rinfo->pc() + delta;
   }
 
-  RelocIterator new_it(new_code, mask);
-  SkipToStackCheck(isolate, &new_it);
-  for (int i = 1; i < index; i++) new_it.next();
-  return new_it.rinfo()->pc() + delta;
+  UNREACHABLE();
+  return NULL;
 }