Add a function to compute loop nesting level to HBasicBlock.

Review URL: http://codereview.chromium.org/7857031

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@9207 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/hydrogen.cc

@@ -220,6 +220,17 @@ bool HBasicBlock::Dominates(HBasicBlock* other) const {
 }
 
 
+int HBasicBlock::LoopNestingDepth() const {
+  const HBasicBlock* current = this;
+  int result  = (current->IsLoopHeader()) ? 1 : 0;
+  while (current->parent_loop_header() != NULL) {
+    current = current->parent_loop_header();
+    result++;
+  }
+  return result;
+}
+
+
 void HBasicBlock::PostProcessLoopHeader(IterationStatement* stmt) {
   ASSERT(IsLoopHeader());
 
@@ -6567,6 +6578,8 @@ void HTracer::Trace(const char* name, HGraph* graph, LChunk* chunk) {
       PrintBlockProperty("dominator", current->dominator()->block_id());
     }
 
+    PrintIntProperty("loop_depth", current->LoopNestingDepth());
+
     if (chunk != NULL) {
       int first_index = current->first_instruction_index();
       int last_index = current->last_instruction_index();

src/hydrogen.h

@@ -102,6 +102,7 @@ class HBasicBlock: public ZoneObject {
   void RemovePhi(HPhi* phi);
   void AddInstruction(HInstruction* instr);
   bool Dominates(HBasicBlock* other) const;
+  int LoopNestingDepth() const;
 
   void SetInitialEnvironment(HEnvironment* env);
   void ClearEnvironment() { last_environment_ = NULL; }