[turbofan] Introduce separate SelectLowering reducer.

Split lowering of Select nodes into a separate graph reducer and be more
clever when lowering to diamonds, i.e. reuse diamonds that have the same
condition and only add more phis to it.

TEST=unittests
R=dcarney@chromium.org

Review URL: https://codereview.chromium.org/702463002

Cr-Commit-Position: refs/heads/master@{#25078}
git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@25078 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

BUILD.gn

@@ -576,6 +576,8 @@ source_set("v8_base") {
     "src/compiler/schedule.h",
     "src/compiler/scheduler.cc",
     "src/compiler/scheduler.h",
+    "src/compiler/select-lowering.cc",
+    "src/compiler/select-lowering.h",
     "src/compiler/simplified-lowering.cc",
     "src/compiler/simplified-lowering.h",
     "src/compiler/simplified-operator-reducer.cc",

src/compiler/js-generic-lowering.cc

@@ -65,7 +65,6 @@ Reduction JSGenericLowering::Reduce(Node* node) {
     Lower##x(node);     \
     break;
     DECLARE_CASE(Branch)
-    DECLARE_CASE(Select)
     JS_OP_LIST(DECLARE_CASE)
 #undef DECLARE_CASE
     default:
@@ -243,23 +242,6 @@ void JSGenericLowering::LowerBranch(Node* node) {
 }
 
 
-void JSGenericLowering::LowerSelect(Node* node) {
-  // TODO(bmeurer): This should probably be moved into a separate file.
-  SelectParameters const& p = SelectParametersOf(node->op());
-  Node* branch = graph()->NewNode(common()->Branch(p.hint()), node->InputAt(0),
-                                  graph()->start());
-  Node* if_true = graph()->NewNode(common()->IfTrue(), branch);
-  Node* vtrue = node->InputAt(1);
-  Node* if_false = graph()->NewNode(common()->IfFalse(), branch);
-  Node* vfalse = node->InputAt(2);
-  Node* merge = graph()->NewNode(common()->Merge(2), if_true, if_false);
-  node->set_op(common()->Phi(p.type(), 2));
-  node->ReplaceInput(0, vtrue);
-  node->ReplaceInput(1, vfalse);
-  node->ReplaceInput(2, merge);
-}
-
-
 void JSGenericLowering::LowerJSUnaryNot(Node* node) {
   Callable callable = CodeFactory::ToBoolean(
       isolate(), ToBooleanStub::RESULT_AS_INVERSE_ODDBALL);

src/compiler/pipeline.cc

@@ -26,6 +26,7 @@
 #include "src/compiler/register-allocator.h"
 #include "src/compiler/schedule.h"
 #include "src/compiler/scheduler.h"
+#include "src/compiler/select-lowering.h"
 #include "src/compiler/simplified-lowering.h"
 #include "src/compiler/simplified-operator-reducer.h"
 #include "src/compiler/typer.h"
@@ -450,9 +451,11 @@ Handle<Code> Pipeline::GenerateCode() {
     PhaseScope phase_scope(pipeline_statistics.get(), "generic lowering");
     SourcePositionTable::Scope pos(data.source_positions(),
                                    SourcePosition::Unknown());
-    JSGenericLowering lowering(info(), data.jsgraph());
+    JSGenericLowering generic(info(), data.jsgraph());
+    SelectLowering select(data.jsgraph()->graph(), data.jsgraph()->common());
     GraphReducer graph_reducer(data.graph());
-    graph_reducer.AddReducer(&lowering);
+    graph_reducer.AddReducer(&generic);
+    graph_reducer.AddReducer(&select);
     graph_reducer.ReduceGraph();
 
     // TODO(jarin, rossberg): Remove UNTYPED once machine typing works.

src/compiler/select-lowering.cc

@@ -0,0 +1,54 @@
+// Copyright 2014 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/select-lowering.h"
+
+#include "src/compiler/common-operator.h"
+#include "src/compiler/generic-node-inl.h"
+#include "src/compiler/graph.h"
+
+namespace v8 {
+namespace internal {
+namespace compiler {
+
+SelectLowering::SelectLowering(Graph* graph, CommonOperatorBuilder* common)
+    : common_(common),
+      graph_(graph),
+      merges_(Merges::key_compare(), Merges::allocator_type(graph->zone())) {}
+
+
+SelectLowering::~SelectLowering() {}
+
+
+Reduction SelectLowering::Reduce(Node* node) {
+  if (node->opcode() != IrOpcode::kSelect) return NoChange();
+  SelectParameters const p = SelectParametersOf(node->op());
+
+  Node* const cond = node->InputAt(0);
+  Node* const control = graph()->start();
+
+  // Check if we already have a diamond for this condition.
+  auto i = merges_.find(cond);
+  if (i == merges_.end()) {
+    // Create a new diamond for this condition and remember its merge node.
+    Node* branch = graph()->NewNode(common()->Branch(p.hint()), cond, control);
+    Node* if_true = graph()->NewNode(common()->IfTrue(), branch);
+    Node* if_false = graph()->NewNode(common()->IfFalse(), branch);
+    Node* merge = graph()->NewNode(common()->Merge(2), if_true, if_false);
+    i = merges_.insert(std::make_pair(cond, merge)).first;
+  }
+
+  DCHECK_EQ(cond, i->first);
+
+  // Create a Phi hanging off the previously determined merge.
+  node->set_op(common()->Phi(p.type(), 2));
+  node->ReplaceInput(0, node->InputAt(1));
+  node->ReplaceInput(1, node->InputAt(2));
+  node->ReplaceInput(2, i->second);
+  return Changed(node);
+}
+
+}  // namespace compiler
+}  // namespace internal
+}  // namespace v8

src/compiler/select-lowering.h

@@ -0,0 +1,46 @@
+// Copyright 2014 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.
+
+#ifndef V8_COMPILER_SELECT_LOWERING_H_
+#define V8_COMPILER_SELECT_LOWERING_H_
+
+#include <map>
+
+#include "src/compiler/graph-reducer.h"
+#include "src/zone-allocator.h"
+
+namespace v8 {
+namespace internal {
+namespace compiler {
+
+// Forward declarations.
+class CommonOperatorBuilder;
+class Graph;
+
+
+// Lowers Select nodes to diamonds.
+class SelectLowering FINAL : public Reducer {
+ public:
+  SelectLowering(Graph* graph, CommonOperatorBuilder* common);
+  ~SelectLowering();
+
+  Reduction Reduce(Node* node) OVERRIDE;
+
+ private:
+  typedef std::map<Node*, Node*, std::less<Node*>,
+                   zone_allocator<std::pair<Node* const, Node*>>> Merges;
+
+  CommonOperatorBuilder* common() const { return common_; }
+  Graph* graph() const { return graph_; }
+
+  CommonOperatorBuilder* common_;
+  Graph* graph_;
+  Merges merges_;
+};
+
+}  // namespace compiler
+}  // namespace internal
+}  // namespace v8
+
+#endif  // V8_COMPILER_SELECT_LOWERING_H_

test/unittests/compiler/select-lowering-unittest.cc

@@ -0,0 +1,62 @@
+// Copyright 2014 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/select-lowering.h"
+#include "test/unittests/compiler/graph-unittest.h"
+#include "test/unittests/compiler/node-test-utils.h"
+#include "testing/gmock-support.h"
+
+using testing::AllOf;
+using testing::Capture;
+using testing::CaptureEq;
+
+namespace v8 {
+namespace internal {
+namespace compiler {
+
+class SelectLoweringTest : public GraphTest {
+ public:
+  SelectLoweringTest() : GraphTest(5), lowering_(graph(), common()) {}
+
+ protected:
+  Reduction Reduce(Node* node) { return lowering_.Reduce(node); }
+
+ private:
+  SelectLowering lowering_;
+};
+
+
+TEST_F(SelectLoweringTest, SelectWithSameConditions) {
+  Node* const p0 = Parameter(0);
+  Node* const p1 = Parameter(1);
+  Node* const p2 = Parameter(2);
+  Node* const p3 = Parameter(3);
+  Node* const p4 = Parameter(4);
+
+  Capture<Node*> branch;
+  Capture<Node*> merge;
+  {
+    Reduction const r =
+        Reduce(graph()->NewNode(common()->Select(kMachInt32), p0, p1, p2));
+    ASSERT_TRUE(r.Changed());
+    EXPECT_THAT(
+        r.replacement(),
+        IsPhi(
+            kMachInt32, p1, p2,
+            AllOf(CaptureEq(&merge),
+                  IsMerge(IsIfTrue(CaptureEq(&branch)),
+                          IsIfFalse(AllOf(CaptureEq(&branch),
+                                          IsBranch(p0, graph()->start())))))));
+  }
+  {
+    Reduction const r =
+        Reduce(graph()->NewNode(common()->Select(kMachInt32), p0, p3, p4));
+    ASSERT_TRUE(r.Changed());
+    EXPECT_THAT(r.replacement(), IsPhi(kMachInt32, p3, p4, CaptureEq(&merge)));
+  }
+}
+
+}  // namespace compiler
+}  // namespace internal
+}  // namespace v8

test/unittests/unittests.gyp

@@ -52,6 +52,7 @@
         'compiler/node-test-utils.cc',
         'compiler/node-test-utils.h',
         'compiler/register-allocator-unittest.cc',
+        'compiler/select-lowering-unittest.cc',
         'compiler/simplified-operator-reducer-unittest.cc',
         'compiler/simplified-operator-unittest.cc',
         'compiler/value-numbering-reducer-unittest.cc',

tools/gyp/v8.gyp

@@ -489,6 +489,8 @@
         '../../src/compiler/schedule.h',
         '../../src/compiler/scheduler.cc',
         '../../src/compiler/scheduler.h',
+        '../../src/compiler/select-lowering.cc',
+        '../../src/compiler/select-lowering.h',
         '../../src/compiler/simplified-lowering.cc',
         '../../src/compiler/simplified-lowering.h',
         '../../src/compiler/simplified-operator-reducer.cc',