Eliminatable CheckMaps replaced with if(true) or if(false).

src/hydrogen-flow-engine.h

Index: src/hydrogen-flow-engine.h
diff --git a/src/hydrogen-flow-engine.h b/src/hydrogen-flow-engine.h
index 4e1275546f611e2401e467484976f73d59b3e784..aadfac2c9917b9a74c60c427c2413f01bfd852a1 100644
--- a/src/hydrogen-flow-engine.h
+++ b/src/hydrogen-flow-engine.h
@@ -124,17 +124,19 @@ class HFlowEngine {
       if (SkipNonDominatedBlock(root, block)) continue;
       State* state = StateAt(block);
 
-      if (block->IsLoopHeader()) {
-        // Apply loop effects before analyzing loop body.
-        ComputeLoopEffects(block)->Apply(state);
-      } else {
-        // Must have visited all predecessors before this block.
-        CheckPredecessorCount(block);
-      }
+      if (block->IsReachable()) {
+        if (block->IsLoopHeader()) {
+          // Apply loop effects before analyzing loop body.
+          ComputeLoopEffects(block)->Apply(state);
+        } else {
+          // Must have visited all predecessors before this block.
+          CheckPredecessorCount(block);
+        }
 
-      // Go through all instructions of the current block, updating the state.
-      for (HInstructionIterator it(block); !it.Done(); it.Advance()) {
-        state = state->Process(it.Current(), zone_);
+        // Go through all instructions of the current block, updating the state.
+        for (HInstructionIterator it(block); !it.Done(); it.Advance()) {
+          state = state->Process(it.Current(), zone_);
+        }
       }
 
       // Propagate the block state forward to all successor blocks.
@@ -142,7 +144,10 @@ class HFlowEngine {
       for (int i = 0; i < max; i++) {
         HBasicBlock* succ = block->end()->SuccessorAt(i);
         IncrementPredecessorCount(succ);
-        if (StateAt(succ) == NULL) {
+        if (succ->IsUnreachable()) {
+          // Unreachable blocks do not modify state of predecessor.
+          SetStateAt(succ, state);

[titzer, 2014/01/14 13:40:32]

This is still not quite correct, because an unreachable successor should still
have the merge of all of its incoming predecessors. I think you can just remove
this first case and it will be correct.

[Igor Sheludko, 2014/01/14 15:28:00]

Done.

+        } else if (StateAt(succ) == NULL) {
           // This is the first state to reach the successor.
           if (max == 1 && succ->predecessors()->length() == 1) {
             // Optimization: successor can inherit this state.
@@ -185,6 +190,7 @@ class HFlowEngine {
         i = member->loop_information()->GetLastBackEdge()->block_id();
       } else {
         // Process all the effects of the block.
+        if (member->IsUnreachable()) continue;
         ASSERT(member->current_loop() == loop);
         for (HInstructionIterator it(member); !it.Done(); it.Advance()) {
           effects->Process(it.Current(), zone_);