Iterative graph traversal in FlowGraph::DiscoverBlocks()

runtime/vm/intermediate_language.cc

Index: runtime/vm/intermediate_language.cc
diff --git a/runtime/vm/intermediate_language.cc b/runtime/vm/intermediate_language.cc
index f56cdde24e4f88b1aa023129b57c3293307c1445..9fa3f62772860cb569544e4ee2cf996e3b10af5a 100644
--- a/runtime/vm/intermediate_language.cc
+++ b/runtime/vm/intermediate_language.cc
@@ -838,10 +838,8 @@ static bool IsMarked(BlockEntryInstr* block,
 void BlockEntryInstr::DiscoverBlocks(
     BlockEntryInstr* predecessor,
     GrowableArray<BlockEntryInstr*>* preorder,
-    GrowableArray<BlockEntryInstr*>* postorder,
     GrowableArray<intptr_t>* parent,
-    intptr_t variable_count,
-    intptr_t fixed_parameter_count) {
+    GrowableArray<BlockEntryEdge>* block_stack) {
   // If this block has a predecessor (i.e., is not the graph entry) we can
   // assume the preorder array is non-empty.
   ASSERT((predecessor == NULL) || !preorder->is_empty());
@@ -885,20 +883,11 @@ void BlockEntryInstr::DiscoverBlocks(
   }
   set_last_instruction(last);
 
-  // Visit the block's successors in reverse so that they appear forwards
-  // the reverse postorder block ordering.
+  // Push the block's successors in reverse so that they are visited from left
+  // to right.
   for (intptr_t i = last->SuccessorCount() - 1; i >= 0; --i) {
-    last->SuccessorAt(i)->DiscoverBlocks(this,
-                                         preorder,
-                                         postorder,
-                                         parent,
-                                         variable_count,
-                                         fixed_parameter_count);
+    block_stack->Add(BlockEntryEdge(this, last->SuccessorAt(i)));
   }
-
-  // 6. Assign postorder number and add the block entry to the list.
-  set_postorder_number(postorder->length());
-  postorder->Add(this);
 }