Iterative graph traversal in FlowGraph::DiscoverBlocks()

runtime/vm/intermediate_language.h

Index: runtime/vm/intermediate_language.h
diff --git a/runtime/vm/intermediate_language.h b/runtime/vm/intermediate_language.h
index c99d69bf9c3c4604060688445e0404b298c666cf..4a04ab896231325e7099b26c92ae95a3eb3aa2e2 100644
--- a/runtime/vm/intermediate_language.h
+++ b/runtime/vm/intermediate_language.h
@@ -20,6 +20,7 @@ DECLARE_FLAG(bool, throw_on_javascript_int_overflow);
 
 class BitVector;
 class BlockEntryInstr;
+class BlockEntryEdge;
 class BoxIntNInstr;
 class BufferFormatter;
 class CatchBlockEntryInstr;
@@ -1137,12 +1138,11 @@ class BlockEntryInstr : public Instruction {
     return parallel_move_;
   }
 
-  // Discover basic-block structure by performing a recursive depth first
+  // Discover basic-block structure by performing an iterative depth first
   // traversal of the instruction graph reachable from this instruction.  As
   // a side effect, the block entry instructions in the graph are assigned
-  // numbers in both preorder and postorder.  The array 'preorder' maps
-  // preorder block numbers to the block entry instruction with that number
-  // and analogously for the array 'postorder'.  The depth first spanning
+  // preorder numbers.  The array 'preorder' maps preorder block numbers to
+  // the block entry instruction with that number.  The depth first spanning
   // tree is recorded in the array 'parent', which maps preorder block
   // numbers to the preorder number of the block's spanning-tree parent.
   // The array 'assigned_vars' maps preorder block numbers to the set of
@@ -1153,10 +1153,8 @@ class BlockEntryInstr : public Instruction {
   void 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);
 
   // Perform a depth first search to prune code not reachable from an OSR
   // entry point.