[turbofan] Redundant branch elimination.

test/unittests/compiler/branch-elimination-unittest.cc

+// Copyright 2015 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "src/compiler/branch-elimination.h"
+#include "src/compiler/js-graph.h"
+#include "src/compiler/linkage.h"
+#include "src/compiler/node-properties.h"
+#include "test/unittests/compiler/compiler-test-utils.h"
+#include "test/unittests/compiler/graph-unittest.h"
+#include "test/unittests/compiler/node-test-utils.h"
+#include "testing/gmock-support.h"
+
+namespace v8 {
+namespace internal {
+namespace compiler {
+
+class BranchEliminationTest : public TypedGraphTest {
+ public:
+  BranchEliminationTest()
+      : machine_(zone(), kMachPtr, MachineOperatorBuilder::kNoFlags) {}
+
+  MachineOperatorBuilder* machine() { return &machine_; }
+
+  void Reduce() {
+    JSOperatorBuilder javascript(zone());
+    JSGraph jsgraph(isolate(), graph(), common(), &javascript, nullptr,
+                    machine());
+    GraphReducer graph_reducer(zone(), graph(), jsgraph.Dead());
+    BranchElimination branch_condition_elimination(&graph_reducer, &jsgraph,
+                                                   zone());
+    graph_reducer.AddReducer(&branch_condition_elimination);
+    graph_reducer.ReduceGraph();
+  }
+
+ private:
+  MachineOperatorBuilder machine_;
+};
+
+
+TEST_F(BranchEliminationTest, NestedBranchSameTrue) {
+  // { return (x ? (x ? 1 : 2) : 3; }
+  // should be reduced to
+  // { return (x ? 1 : 3; }
+  Node* condition = Parameter(0);
+  Node* outer_branch =
+      graph()->NewNode(common()->Branch(), condition, graph()->start());
+
+  Node* outer_if_true = graph()->NewNode(common()->IfTrue(), outer_branch);
+  Node* inner_branch =
+      graph()->NewNode(common()->Branch(), condition, outer_if_true);
+  Node* inner_if_true = graph()->NewNode(common()->IfTrue(), inner_branch);
+  Node* inner_if_false = graph()->NewNode(common()->IfFalse(), inner_branch);
+  Node* inner_merge =
+      graph()->NewNode(common()->Merge(2), inner_if_true, inner_if_false);
+  Node* inner_phi =
+      graph()->NewNode(common()->Phi(kMachInt32, 2), Int32Constant(1),
+                       Int32Constant(2), inner_merge);
+
+  Node* outer_if_false = graph()->NewNode(common()->IfFalse(), outer_branch);
+  Node* outer_merge =
+      graph()->NewNode(common()->Merge(2), inner_merge, outer_if_false);
+  Node* outer_phi = graph()->NewNode(common()->Phi(kMachInt32, 2), inner_phi,
+                                     Int32Constant(3), outer_merge);
+
+  Node* ret = graph()->NewNode(common()->Return(), outer_phi, graph()->start(),
+                               outer_merge);
+  graph()->SetEnd(graph()->NewNode(common()->End(1), ret));
+
+  Reduce();
+
+  // Outer branch should not be rewritten, the inner branch should be discarded.
+  EXPECT_THAT(outer_branch, IsBranch(condition, graph()->start()));
+  EXPECT_THAT(inner_phi,
+              IsPhi(kMachInt32, IsInt32Constant(1), IsInt32Constant(2),
+                    IsMerge(outer_if_true, IsDead())));
+}
+
+
+TEST_F(BranchEliminationTest, NestedBranchSameFalse) {
+  // { return (x ? 1 : (x ? 2 : 3); }
+  // should be reduced to
+  // { return (x ? 1 : 3; }
+  Node* condition = Parameter(0);
+  Node* outer_branch =
+      graph()->NewNode(common()->Branch(), condition, graph()->start());
+
+  Node* outer_if_true = graph()->NewNode(common()->IfTrue(), outer_branch);
+
+  Node* outer_if_false = graph()->NewNode(common()->IfFalse(), outer_branch);
+  Node* inner_branch =
+      graph()->NewNode(common()->Branch(), condition, outer_if_false);
+  Node* inner_if_true = graph()->NewNode(common()->IfTrue(), inner_branch);
+  Node* inner_if_false = graph()->NewNode(common()->IfFalse(), inner_branch);
+  Node* inner_merge =
+      graph()->NewNode(common()->Merge(2), inner_if_true, inner_if_false);
+  Node* inner_phi =
+      graph()->NewNode(common()->Phi(kMachInt32, 2), Int32Constant(2),
+                       Int32Constant(3), inner_merge);
+
+  Node* outer_merge =
+      graph()->NewNode(common()->Merge(2), outer_if_true, inner_merge);
+  Node* outer_phi = graph()->NewNode(common()->Phi(kMachInt32, 2),
+                                     Int32Constant(1), inner_phi, outer_merge);
+
+  Node* ret = graph()->NewNode(common()->Return(), outer_phi, graph()->start(),
+                               outer_merge);
+  graph()->SetEnd(graph()->NewNode(common()->End(1), ret));
+
+  Reduce();
+
+  // Outer branch should not be rewritten, the inner branch should be discarded.
+  EXPECT_THAT(outer_branch, IsBranch(condition, graph()->start()));
+  EXPECT_THAT(inner_phi,
+              IsPhi(kMachInt32, IsInt32Constant(2), IsInt32Constant(3),
+                    IsMerge(IsDead(), outer_if_false)));
+}
+
+
+TEST_F(BranchEliminationTest, BranchAfterDiamond) {
+  // { var y = x ? 1 : 2; return y + x ? 3 : 4; }
+  // should not be reduced.
+  Node* condition = Parameter(0);
+
+  Node* branch1 =
+      graph()->NewNode(common()->Branch(), condition, 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), Int32Constant(1),
+                                Int32Constant(2), merge1);
+
+  Node* branch2 = graph()->NewNode(common()->Branch(), condition, 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* phi2 = graph()->NewNode(common()->Phi(kMachInt32, 2), Int32Constant(3),
+                                Int32Constant(4), merge1);
+
+
+  Node* add = graph()->NewNode(machine()->Int32Add(), phi1, phi2);
+  Node* ret =
+      graph()->NewNode(common()->Return(), add, graph()->start(), merge2);
+  graph()->SetEnd(graph()->NewNode(common()->End(1), ret));
+
+  Reduce();
+
+  // Outer branch should not be rewritten, the inner branch condition should
+  // be true.
+  EXPECT_THAT(branch1, IsBranch(condition, graph()->start()));
+  EXPECT_THAT(branch2, IsBranch(condition, merge1));
+}
+
+
+TEST_F(BranchEliminationTest, BranchInsideLoopSame) {
+  // if (x) while (x) { return 2; } else { return 1; }
+  // should be rewritten to
+  // if (x) while (true) { return 2; } else { return 1; }
+
+  Node* condition = Parameter(0);
+
+  Node* outer_branch =
+      graph()->NewNode(common()->Branch(), condition, graph()->start());
+  Node* outer_if_true = graph()->NewNode(common()->IfTrue(), outer_branch);
+
+
+  Node* loop = graph()->NewNode(common()->Loop(1), outer_if_true);
+  Node* effect =
+      graph()->NewNode(common()->EffectPhi(1), graph()->start(), loop);
+
+  Node* inner_branch = graph()->NewNode(common()->Branch(), condition, loop);
+
+  Node* inner_if_true = graph()->NewNode(common()->IfTrue(), inner_branch);
+  Node* ret1 = graph()->NewNode(common()->Return(), Int32Constant(2), effect,
+                                inner_if_true);
+
+  Node* inner_if_false = graph()->NewNode(common()->IfFalse(), inner_branch);
+  loop->AppendInput(zone(), inner_if_false);
+  NodeProperties::ChangeOp(loop, common()->Loop(2));
+  effect->InsertInput(zone(), 1, effect);
+  NodeProperties::ChangeOp(effect, common()->EffectPhi(2));
+
+  Node* outer_if_false = graph()->NewNode(common()->IfFalse(), outer_branch);
+  Node* outer_merge =
+      graph()->NewNode(common()->Merge(2), loop, outer_if_false);
+  Node* outer_ephi = graph()->NewNode(common()->EffectPhi(2), effect,
+                                      graph()->start(), outer_merge);
+
+  Node* ret2 = graph()->NewNode(common()->Return(), Int32Constant(1),
+                                outer_ephi, outer_merge);
+
+  Node* terminate = graph()->NewNode(common()->Terminate(), effect, loop);
+  graph()->SetEnd(graph()->NewNode(common()->End(3), ret1, ret2, terminate));
+
+  Reduce();
+
+  // Outer branch should not be rewritten, the inner branch should be discarded.
+  EXPECT_THAT(outer_branch, IsBranch(condition, graph()->start()));
+  EXPECT_THAT(ret1, IsReturn(IsInt32Constant(2), effect, loop));
+}
+
+}  // namespace compiler
+}  // namespace internal
+}  // namespace v8