Avoid copying flow-sensitive state when only a goto separates blocks.

BUG=
R=mvstanton@chromium.org

Review URL: https://codereview.chromium.org/48353007

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@18090 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

diff --git a/src/hydrogen-flow-engine.h b/src/hydrogen-flow-engine.h
index dfe43ec..4e12755 100644 (file)
--- a/src/hydrogen-flow-engine.h
+++ b/src/hydrogen-flow-engine.h
@@ -138,12 +138,19 @@ class HFlowEngine {
       }
 
       // Propagate the block state forward to all successor blocks.
-      for (int i = 0; i < block->end()->SuccessorCount(); i++) {
+      int max = block->end()->SuccessorCount();
+      for (int i = 0; i < max; i++) {
         HBasicBlock* succ = block->end()->SuccessorAt(i);
         IncrementPredecessorCount(succ);
         if (StateAt(succ) == NULL) {
           // This is the first state to reach the successor.
-          SetStateAt(succ, state->Copy(succ, zone_));
+          if (max == 1 && succ->predecessors()->length() == 1) {
+            // Optimization: successor can inherit this state.
+            SetStateAt(succ, state);
+          } else {
+            // Successor needs a copy of the state.
+            SetStateAt(succ, state->Copy(succ, zone_));
+          }
         } else {
           // Merge the current state with the state already at the successor.
           SetStateAt(succ, state->Merge(succ, StateAt(succ), zone_));