[turbofan] Remove another premature optimization from ControlReducer.

We never hit the phi case for DecideCondition in practice, since a more
general optimization is already performed by typing and constant
propagation.

R=jarin@chromium.org,mstarzinger@chromium.org

Review URL: https://codereview.chromium.org/1186973005

Cr-Commit-Position: refs/heads/master@{#29102}

src/compiler/control-reducer.cc

@@ -87,7 +87,7 @@ class ControlReducerImpl final : public AdvancedReducer {
   }
 
   // Try to statically fold a condition.
-  Decision DecideCondition(Node* cond, bool recurse = true) {
+  Decision DecideCondition(Node* cond) {
     switch (cond->opcode()) {
       case IrOpcode::kInt32Constant:
         return Int32Matcher(cond).Is(0) ? kFalse : kTrue;
@@ -98,19 +98,6 @@ class ControlReducerImpl final : public AdvancedReducer {
             HeapObjectMatcher<Object>(cond).Value().handle();
         return object->BooleanValue() ? kTrue : kFalse;
       }
-      case IrOpcode::kPhi: {
-        if (!recurse) return kUnknown;  // Only go one level deep checking phis.
-        Decision result = kUnknown;
-        // Check if all inputs to a phi result in the same decision.
-        for (int i = cond->op()->ValueInputCount() - 1; i >= 0; i--) {
-          // Recurse only one level, since phis can be involved in cycles.
-          Decision decision = DecideCondition(cond->InputAt(i), false);
-          if (decision == kUnknown) return kUnknown;
-          if (result == kUnknown) result = decision;
-          if (result != decision) return kUnknown;
-        }
-        return result;
-      }
       default:
         break;
     }

test/unittests/compiler/control-reducer-unittest.cc

@@ -22,10 +22,10 @@ namespace v8 {
 namespace internal {
 namespace compiler {
 
-class ControlReducerTest : public TypedGraphTest {
+class ControlReducerTest : public GraphTest {
  public:
   ControlReducerTest()
-      : TypedGraphTest(1),
+      : GraphTest(1),
         machine_(zone()),
         javascript_(zone()),
         jsgraph_(isolate(), graph(), common(), &javascript_, &machine_) {}
@@ -53,98 +53,6 @@ class ControlReducerTest : public TypedGraphTest {
 };
 
 
-TEST_F(ControlReducerTest, PhiAsInputToBranch_true) {
-  Node* p0 = Parameter(0);
-  Node* branch1 = graph()->NewNode(common()->Branch(), p0, graph()->start());
-  Node* if_true1 = graph()->NewNode(common()->IfTrue(), branch1);
-  Node* if_false1 = graph()->NewNode(common()->IfFalse(), branch1);
-  Node* merge1 = graph()->NewNode(common()->Merge(2), if_true1, if_false1);
-  Node* phi1 = graph()->NewNode(common()->Phi(kMachInt32, 2),
-                                jsgraph()->Int32Constant(1),
-                                jsgraph()->Int32Constant(2), merge1);
-
-  Node* branch2 = graph()->NewNode(common()->Branch(), phi1, merge1);
-  Node* if_true2 = graph()->NewNode(common()->IfTrue(), branch2);
-  Node* if_false2 = graph()->NewNode(common()->IfFalse(), branch2);
-  Node* merge2 = graph()->NewNode(common()->Merge(2), if_true2, if_false2);
-  Node* result = graph()->NewNode(common()->Phi(kMachInt32, 2),
-                                  jsgraph()->Int32Constant(11),
-                                  jsgraph()->Int32Constant(22), merge2);
-
-  Node* ret =
-      graph()->NewNode(common()->Return(), result, graph()->start(), merge2);
-  graph()->end()->ReplaceInput(0, ret);
-
-  ReduceGraph();
-
-  // First diamond is not reduced.
-  EXPECT_THAT(merge1, IsMerge(IsIfTrue(branch1), IsIfFalse(branch1)));
-
-  // Second diamond should be folded away.
-  EXPECT_THAT(graph()->end(),
-              IsEnd(IsReturn(IsInt32Constant(11), graph()->start(), merge1)));
-}
-
-
-TEST_F(ControlReducerTest, PhiAsInputToBranch_false) {
-  Node* p0 = Parameter(0);
-  Node* branch1 = graph()->NewNode(common()->Branch(), p0, graph()->start());
-  Node* if_true1 = graph()->NewNode(common()->IfTrue(), branch1);
-  Node* if_false1 = graph()->NewNode(common()->IfFalse(), branch1);
-  Node* merge1 = graph()->NewNode(common()->Merge(2), if_true1, if_false1);
-  Node* phi1 = graph()->NewNode(common()->Phi(kMachInt32, 2),
-                                jsgraph()->Int32Constant(0),
-                                jsgraph()->BooleanConstant(false), merge1);
-
-  Node* branch2 = graph()->NewNode(common()->Branch(), phi1, merge1);
-  Node* if_true2 = graph()->NewNode(common()->IfTrue(), branch2);
-  Node* if_false2 = graph()->NewNode(common()->IfFalse(), branch2);
-  Node* merge2 = graph()->NewNode(common()->Merge(2), if_true2, if_false2);
-  Node* result = graph()->NewNode(common()->Phi(kMachInt32, 2),
-                                  jsgraph()->Int32Constant(11),
-                                  jsgraph()->Int32Constant(22), merge2);
-
-  Node* ret =
-      graph()->NewNode(common()->Return(), result, graph()->start(), merge2);
-  graph()->end()->ReplaceInput(0, ret);
-
-  ReduceGraph();
-
-  // First diamond is not reduced.
-  EXPECT_THAT(merge1, IsMerge(IsIfTrue(branch1), IsIfFalse(branch1)));
-
-  // Second diamond should be folded away.
-  EXPECT_THAT(graph()->end(),
-              IsEnd(IsReturn(IsInt32Constant(22), graph()->start(), merge1)));
-}
-
-
-TEST_F(ControlReducerTest, PhiAsInputToBranch_unknown_true) {
-  Node* p0 = Parameter(0);
-  Node* phi0 = graph()->NewNode(common()->Phi(kMachInt32, 2), p0,
-                                jsgraph()->Int32Constant(1), graph()->start());
-  Node* branch1 = graph()->NewNode(common()->Branch(), phi0, graph()->start());
-  Node* if_true1 = graph()->NewNode(common()->IfTrue(), branch1);
-  Node* if_false1 = graph()->NewNode(common()->IfFalse(), branch1);
-  Node* merge1 = graph()->NewNode(common()->Merge(2), if_true1, if_false1);
-  Node* phi1 = graph()->NewNode(common()->Phi(kMachInt32, 2),
-                                jsgraph()->Int32Constant(111),
-                                jsgraph()->Int32Constant(222), merge1);
-
-  Node* ret =
-      graph()->NewNode(common()->Return(), phi1, graph()->start(), merge1);
-  graph()->end()->ReplaceInput(0, ret);
-
-  ReduceGraph();
-
-  // Branch should not be folded.
-  EXPECT_THAT(phi1,
-              IsPhi(kMachInt32, IsInt32Constant(111), IsInt32Constant(222),
-                    IsMerge(IsIfTrue(branch1), IsIfFalse(branch1))));
-  EXPECT_THAT(graph()->end(), IsEnd(IsReturn(phi1, graph()->start(), merge1)));
-}
-
-
 TEST_F(ControlReducerTest, SelectPhi) {
   Node* p0 = Parameter(0);
   const MachineType kType = kMachInt32;