[turbofan] Also update the BranchHint when merging a BooleanNot.

src/compiler/common-operator-reducer.cc

Index: src/compiler/common-operator-reducer.cc
diff --git a/src/compiler/common-operator-reducer.cc b/src/compiler/common-operator-reducer.cc
index 1ed05f1834bf7b214db79526d8fc5a2f3698c736..24760dc2f596398de81f39aab9d9819d6b263124 100644
--- a/src/compiler/common-operator-reducer.cc
+++ b/src/compiler/common-operator-reducer.cc
@@ -99,6 +99,17 @@ Reduction CommonOperatorReducer::ReduceBranch(Node* node) {
     // since we tell the graph reducer that the {branch} was changed and the
     // graph reduction logic will ensure that the uses are revisited properly.
     node->ReplaceInput(0, cond->InputAt(0));
+    // Negative the hint for {branch}.

[Sven Panne, 2015/06/26 11:40:56]

Why do we need the switch at all? Isn't the simple one-liner

  node->set_op(common()->Branch(NegateBranch(BranchHintOf(node->op()));

enough for all cases? Then comment would be superfluous, BTW. If it's a
nano-optimization, please add a comment why it's necessary.

[Benedikt Meurer, 2015/06/26 11:43:40]

Done.

+    switch (BranchHintOf(node->op())) {
+      case BranchHint::kTrue:
+        node->set_op(common()->Branch(BranchHint::kFalse));
+        break;
+      case BranchHint::kFalse:
+        node->set_op(common()->Branch(BranchHint::kTrue));
+        break;
+      case BranchHint::kNone:
+        break;
+    }
     return Changed(node);
   }
   Decision const decision = DecideCondition(cond);