Use worklist to find out Phis that could not be truncated to int32

Review URL: https://codereview.chromium.org/13950013

Patch from Haitao Feng <haitao.feng@intel.com>.

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@14528 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/hydrogen.cc

@@ -4075,19 +4075,17 @@ void HGraph::InsertRepresentationChanges() {
   // int32-phis allow truncation and iteratively remove the ones that
   // are used in an operation that does not allow a truncating
   // conversion.
-  // TODO(fschneider): Replace this with a worklist-based iteration.
+  ZoneList<HPhi*> worklist(8, zone());
+
   for (int i = 0; i < phi_list()->length(); i++) {
     HPhi* phi = phi_list()->at(i);
     if (phi->representation().IsInteger32()) {
       phi->SetFlag(HValue::kTruncatingToInt32);
     }
   }
-  bool change = true;
-  while (change) {
-    change = false;
+
   for (int i = 0; i < phi_list()->length(); i++) {
     HPhi* phi = phi_list()->at(i);
-      if (!phi->CheckFlag(HValue::kTruncatingToInt32)) continue;
     for (HUseIterator it(phi->uses()); !it.Done(); it.Advance()) {
       // If a Phi is used as a non-truncating int32 or as a double,
       // clear its "truncating" flag.
@@ -4102,11 +4100,27 @@ void HGraph::InsertRepresentationChanges() {
                  phi->id(), it.value()->id(), it.value()->Mnemonic());
         }
         phi->ClearFlag(HValue::kTruncatingToInt32);
-          change = true;
+        worklist.Add(phi, zone());
         break;
       }
     }
   }
+
+  while (!worklist.is_empty()) {
+    HPhi* current = worklist.RemoveLast();
+    for (int i = 0; i < current->OperandCount(); ++i) {
+      HValue* input = current->OperandAt(i);
+      if (input->IsPhi() &&
+          input->representation().IsInteger32() &&
+          input->CheckFlag(HValue::kTruncatingToInt32)) {
+        if (FLAG_trace_representation) {
+          PrintF("#%d Phi is not truncating because of #%d %s\n",
+                 input->id(), current->id(), current->Mnemonic());
+        }
+        input->ClearFlag(HValue::kTruncatingToInt32);
+        worklist.Add(HPhi::cast(input), zone());
+      }
+    }
   }
 
   for (int i = 0; i < blocks_.length(); ++i) {