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

src/hydrogen-check-elimination.cc

Index: src/hydrogen-check-elimination.cc
diff --git a/src/hydrogen-check-elimination.cc b/src/hydrogen-check-elimination.cc
index ae11042ba1e449b3c33b2d036ca36477165142d6..90e8450c821a17081c8bbd7dc9991ee28e792070 100644
--- a/src/hydrogen-check-elimination.cc
+++ b/src/hydrogen-check-elimination.cc
@@ -132,8 +132,10 @@ class HCheckTable : public ZoneObject {
 
     // Branch-sensitive analysis for certain comparisons may add more facts
     // to the state for the successor on the true branch.
-    HControlInstruction* end = succ->predecessors()->at(0)->end();
-    if (succ->predecessors()->length() == 1 && end->SuccessorAt(0) == succ) {
+    HBasicBlock* pred_block = succ->predecessors()->at(0);
+    HControlInstruction* end = pred_block->end();
+    if (succ->predecessors()->length() == 1 && end->SuccessorAt(0) == succ &&
+        pred_block->IsReachable()) {
       if (end->IsCompareMap()) {
         // Learn on the true branch of if(CompareMap(x)).
         HCompareMap* cmp = HCompareMap::cast(end);
@@ -311,14 +313,27 @@ class HCheckTable : public ZoneObject {
   void ReduceCompareMap(HCompareMap* instr) {
     MapSet maps = FindMaps(instr->value()->ActualValue());
     if (maps == NULL) return;
+
+    TRACE(("CompareMap for #%d at B%d ",
+        instr->value()->ActualValue()->id(), instr->block()->block_id()));
+
     if (maps->Contains(instr->map())) {
       if (maps->size() == 1) {
-        // TODO(titzer): replace with goto true branch
         INC_STAT(compares_true_);
+
+        TRACE(("replaced with goto B%d (true target)\n",
+               instr->SuccessorAt(0)->block_id()));
+
+        instr->block()->ReplaceControlWithGotoSuccessor(0);
+      } else {
+        TRACE(("can't be replaced with goto: ambiguous set of maps\n"));
       }
     } else {
-      // TODO(titzer): replace with goto false branch
       INC_STAT(compares_false_);
+      TRACE(("replaced with goto B%d (false target)\n",
+             instr->SuccessorAt(1)->block_id()));
+
+      instr->block()->ReplaceControlWithGotoSuccessor(1);
     }
   }