[wasm][revec] Introduce LinearScheduler

Add a simple, linear-time scheduler to check whether two nodes can be
scheduled to a same basic block without actually building basic blocks.

Bug: v8:12716
Change-Id: I20506f28a9126f881b7e4748f54b12551967ba76
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3388910Reviewed-by: Almothana Athamneh <almuthanna@chromium.org>
Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Commit-Queue: Hao A Xu <hao.a.xu@intel.com>
Cr-Commit-Position: refs/heads/main@{#81015}

BUILD.gn

@@ -3626,6 +3626,10 @@ v8_header_set("v8_internal_headers") {
     ]
   }
 
+  if (v8_enable_wasm_simd256_revec) {
+    sources += [ "src/compiler/linear-scheduler.h" ]
+  }
+
   if (!v8_enable_third_party_heap) {
     sources += filter_include(v8_third_party_heap_files, [ "*.h" ])
   } else {
@@ -4071,6 +4075,10 @@ if (v8_enable_webassembly) {
   ]
 }
 
+if (v8_enable_wasm_simd256_revec) {
+  v8_compiler_sources += [ "src/compiler/linear-scheduler.cc" ]
+}
+
 # The src/compiler files with optimizations.
 v8_source_set("v8_compiler_opt") {
   visibility = [ ":*" ]  # Only targets in this file can depend on this.

gni/v8.gni

@@ -69,6 +69,9 @@ declare_args() {
   # executed as standard JavaScript instead.
   v8_enable_webassembly = ""
 
+  # Enable 256-bit long vector re-vectorization pass in WASM compilation pipeline.
+  v8_enable_wasm_simd256_revec = false
+
   # Enable runtime call stats.
   v8_enable_runtime_call_stats = !is_on_release_branch
 

src/compiler/linear-scheduler.cc

+// Copyright 2013 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/linear-scheduler.h"
+
+#include "src/compiler/graph.h"
+#include "src/compiler/node-properties.h"
+#include "src/compiler/node.h"
+#include "src/zone/zone-containers.h"
+
+namespace v8 {
+namespace internal {
+namespace compiler {
+
+LinearScheduler::LinearScheduler(Zone* zone, Graph* graph)
+    : graph_(graph), control_level_(zone), early_schedule_position_(zone) {
+  ComputeControlLevel();
+}
+
+void LinearScheduler::ComputeControlLevel() {
+  Node* start = graph_->start();
+  SetControlLevel(start, 0);
+
+  // Do BFS from the start node and compute the level of
+  // each control node.
+  std::queue<Node*> queue({start});
+  while (!queue.empty()) {
+    Node* node = queue.front();
+    int level = GetControlLevel(node);
+    queue.pop();
+    for (Edge const edge : node->use_edges()) {
+      if (!NodeProperties::IsControlEdge(edge)) continue;
+      Node* use = edge.from();
+      if (control_level_.find(use) == control_level_.end() &&
+          use->opcode() != IrOpcode::kEnd) {
+        SetControlLevel(use, level + 1);
+        queue.push(use);
+      }
+    }
+  }
+}
+
+Node* LinearScheduler::GetEarlySchedulePosition(Node* node) {
+  DCHECK(!NodeProperties::IsControl(node));
+
+  auto it = early_schedule_position_.find(node);
+  if (it != early_schedule_position_.end()) return it->second;
+
+  std::stack<NodeState> stack;
+  stack.push({node, nullptr, 0});
+  Node* early_schedule_position = nullptr;
+  while (!stack.empty()) {
+    NodeState& top = stack.top();
+    if (NodeProperties::IsPhi(top.node)) {
+      // For phi node, the early schedule position is its control node.
+      early_schedule_position = NodeProperties::GetControlInput(top.node);
+    } else if (top.node->InputCount() == 0) {
+      // For node without inputs, the early schedule position is start node.
+      early_schedule_position = graph_->start();
+    } else {
+      // For others, the early schedule position is one of its inputs' early
+      // schedule position with maximal level.
+      if (top.input_index == top.node->InputCount()) {
+        // All inputs are visited, set early schedule position.
+        early_schedule_position = top.early_schedule_position;
+      } else {
+        // Visit top's input and find its early schedule position.
+        Node* input = top.node->InputAt(top.input_index);
+        Node* input_early_schedule_position = nullptr;
+        if (NodeProperties::IsControl(input)) {
+          input_early_schedule_position = input;
+        } else {
+          auto it = early_schedule_position_.find(input);
+          if (it != early_schedule_position_.end())
+            input_early_schedule_position = it->second;
+        }
+        if (input_early_schedule_position != nullptr) {
+          if (top.early_schedule_position == nullptr ||
+              GetControlLevel(top.early_schedule_position) <
+                  GetControlLevel(input_early_schedule_position)) {
+            top.early_schedule_position = input_early_schedule_position;
+          }
+          top.input_index += 1;
+        } else {
+          top.input_index += 1;
+          stack.push({input, nullptr, 0});
+        }
+        continue;
+      }
+    }
+
+    // Found top's early schedule position, set it to the cache and pop it out
+    // of the stack.
+    SetEarlySchedulePosition(top.node, early_schedule_position);
+    stack.pop();
+    // Update early schedule position of top's use.
+    if (!stack.empty()) {
+      NodeState& use = stack.top();
+      if (use.early_schedule_position == nullptr ||
+          GetControlLevel(use.early_schedule_position) <
+              GetControlLevel(top.early_schedule_position)) {
+        use.early_schedule_position = top.early_schedule_position;
+      }
+    }
+  }
+
+  DCHECK(early_schedule_position != nullptr);
+  return early_schedule_position;
+}
+
+bool LinearScheduler::SameBasicBlock(Node* node0, Node* node1) {
+  Node* early_schedule_position0 = NodeProperties::IsControl(node0)
+                                       ? node0
+                                       : GetEarlySchedulePosition(node0);
+  Node* early_schedule_position1 = NodeProperties::IsControl(node1)
+                                       ? node1
+                                       : GetEarlySchedulePosition(node1);
+  return early_schedule_position0 == early_schedule_position1;
+}
+
+}  // namespace compiler
+}  // namespace internal
+}  // namespace v8

src/compiler/linear-scheduler.h

+// Copyright 2013 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_LINEAR_SCHEDULER_H_
+#define V8_COMPILER_LINEAR_SCHEDULER_H_
+
+#include "src/base/flags.h"
+#include "src/common/globals.h"
+#include "src/compiler/node.h"
+#include "src/compiler/opcodes.h"
+#include "src/compiler/zone-stats.h"
+#include "src/zone/zone-containers.h"
+
+namespace v8 {
+namespace internal {
+namespace compiler {
+
+// A simple, linear-time scheduler to check whether two nodes are in a same
+// basic block without actually building basic block.
+class V8_EXPORT_PRIVATE LinearScheduler {
+ public:
+  explicit LinearScheduler(Zone* zone, Graph* graph);
+  bool SameBasicBlock(Node* node0, Node* node1);
+  // Get a node's early schedule position. It is the earliest block (represented
+  // by a control node) where a node could be scheduled.
+  Node* GetEarlySchedulePosition(Node* node);
+
+ private:
+  // Compute the level of each control node. The level is defined by the
+  // shortest control path from the start node.
+  void ComputeControlLevel();
+
+  struct NodeState {
+    Node* node;
+    Node* early_schedule_position;
+    int input_index;
+  };
+
+  int GetControlLevel(Node* control) const {
+    auto it = control_level_.find(control);
+    DCHECK(it != control_level_.end());
+    return it->second;
+  }
+
+  void SetControlLevel(Node* control, int level) {
+    DCHECK(control_level_.find(control) == control_level_.end());
+    control_level_[control] = level;
+  }
+
+  void SetEarlySchedulePosition(Node* node, Node* early_schedule_position) {
+    early_schedule_position_[node] = early_schedule_position;
+  }
+
+  Graph* graph_;
+  // A map from a control node to the control level of the corresponding basic
+  // block.
+  ZoneMap<Node*, int> control_level_;
+  // A map from a non-control node to its early schedule position.
+  ZoneMap<Node*, Node*> early_schedule_position_;
+};
+
+}  // namespace compiler
+}  // namespace internal
+}  // namespace v8
+
+#endif  // V8_COMPILER_LINEAR_SCHEDULER_H_

test/unittests/BUILD.gn

@@ -494,6 +494,10 @@ v8_source_set("unittests_sources") {
     ]
   }
 
+  if (v8_enable_wasm_simd256_revec) {
+    sources += [ "compiler/linear-scheduler-unittest.cc" ]
+  }
+
   if (v8_enable_wasm_gdb_remote_debugging) {
     sources += [ "wasm/wasm-gdbserver-unittest.cc" ]
   }

test/unittests/compiler/linear-scheduler-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/linear-scheduler.h"
+
+#include "src/compiler/access-builder.h"
+#include "src/compiler/common-operator.h"
+#include "src/compiler/graph.h"
+#include "src/compiler/node.h"
+#include "src/compiler/opcodes.h"
+#include "src/compiler/operator.h"
+#include "src/compiler/simplified-operator.h"
+#include "test/unittests/compiler/compiler-test-utils.h"
+#include "test/unittests/test-utils.h"
+#include "testing/gmock/include/gmock/gmock.h"
+
+using testing::AnyOf;
+
+namespace v8 {
+namespace internal {
+namespace compiler {
+
+class LinearSchedulerTest : public TestWithIsolateAndZone {
+ public:
+  LinearSchedulerTest()
+      : TestWithIsolateAndZone(kCompressGraphZone),
+        graph_(zone()),
+        common_(zone()),
+        simplified_(zone()) {}
+
+  Graph* graph() { return &graph_; }
+  CommonOperatorBuilder* common() { return &common_; }
+  SimplifiedOperatorBuilder* simplified() { return &simplified_; }
+
+ private:
+  Graph graph_;
+  CommonOperatorBuilder common_;
+  SimplifiedOperatorBuilder simplified_;
+};
+
+namespace {
+
+const Operator kIntAdd(IrOpcode::kInt32Add, Operator::kPure, "Int32Add", 2, 0,
+                       0, 1, 0, 0);
+
+}  // namespace
+
+TEST_F(LinearSchedulerTest, BuildSimpleScheduleEmpty) {
+  Node* start = graph()->NewNode(common()->Start(0));
+  graph()->SetStart(start);
+
+  Node* end = graph()->NewNode(common()->End(1), graph()->start());
+  graph()->SetEnd(end);
+
+  LinearScheduler simple_scheduler(zone(), graph());
+  EXPECT_FALSE(simple_scheduler.SameBasicBlock(start, end));
+}
+
+TEST_F(LinearSchedulerTest, BuildSimpleScheduleOneParameter) {
+  graph()->SetStart(graph()->NewNode(common()->Start(0)));
+
+  Node* p1 = graph()->NewNode(common()->Parameter(0), graph()->start());
+  Node* zero = graph()->NewNode(common()->Int32Constant(0));
+  Node* ret = graph()->NewNode(common()->Return(), zero, p1, graph()->start(),
+                               graph()->start());
+
+  graph()->SetEnd(graph()->NewNode(common()->End(1), ret));
+
+  LinearScheduler simple_scheduler(zone(), graph());
+  EXPECT_TRUE(simple_scheduler.SameBasicBlock(p1, zero));
+  EXPECT_FALSE(simple_scheduler.SameBasicBlock(zero, ret));
+}
+
+TARGET_TEST_F(LinearSchedulerTest, FloatingDiamond) {
+  Node* start = graph()->NewNode(common()->Start(1));
+  graph()->SetStart(start);
+
+  Node* cond = graph()->NewNode(common()->Parameter(0), start);
+  Node* tv = graph()->NewNode(common()->Int32Constant(6));
+  Node* fv = graph()->NewNode(common()->Int32Constant(7));
+  Node* br = graph()->NewNode(common()->Branch(), cond, start);
+  Node* t = graph()->NewNode(common()->IfTrue(), br);
+  Node* f = graph()->NewNode(common()->IfFalse(), br);
+  Node* m = graph()->NewNode(common()->Merge(2), t, f);
+  Node* phi = graph()->NewNode(common()->Phi(MachineRepresentation::kTagged, 2),
+                               tv, fv, m);
+  Node* zero = graph()->NewNode(common()->Int32Constant(0));
+  Node* ret = graph()->NewNode(common()->Return(), zero, phi, start, start);
+  Node* end = graph()->NewNode(common()->End(1), ret);
+
+  graph()->SetEnd(end);
+
+  LinearScheduler simple_scheduler(zone(), graph());
+  EXPECT_FALSE(simple_scheduler.SameBasicBlock(t, f));
+  EXPECT_FALSE(simple_scheduler.SameBasicBlock(phi, t));
+  EXPECT_FALSE(simple_scheduler.SameBasicBlock(phi, f));
+}
+
+TARGET_TEST_F(LinearSchedulerTest, NestedFloatingDiamonds) {
+  Node* start = graph()->NewNode(common()->Start(2));
+  graph()->SetStart(start);
+
+  Node* p0 = graph()->NewNode(common()->Parameter(0), start);
+
+  Node* tv = graph()->NewNode(common()->Int32Constant(7));
+  Node* br = graph()->NewNode(common()->Branch(), p0, graph()->start());
+  Node* t = graph()->NewNode(common()->IfTrue(), br);
+  Node* f = graph()->NewNode(common()->IfFalse(), br);
+
+  Node* map = graph()->NewNode(
+      simplified()->LoadElement(AccessBuilder::ForFixedArrayElement()), p0, p0,
+      start, f);
+  Node* br1 = graph()->NewNode(common()->Branch(), map, graph()->start());
+  Node* t1 = graph()->NewNode(common()->IfTrue(), br1);
+  Node* f1 = graph()->NewNode(common()->IfFalse(), br1);
+  Node* m1 = graph()->NewNode(common()->Merge(2), t1, f1);
+  Node* ttrue = graph()->NewNode(common()->Int32Constant(1));
+  Node* ffalse = graph()->NewNode(common()->Int32Constant(0));
+  Node* phi1 = graph()->NewNode(
+      common()->Phi(MachineRepresentation::kTagged, 2), ttrue, ffalse, m1);
+
+  Node* m = graph()->NewNode(common()->Merge(2), t, f);
+  Node* phi = graph()->NewNode(common()->Phi(MachineRepresentation::kTagged, 2),
+                               tv, phi1, m);
+  Node* ephi1 = graph()->NewNode(common()->EffectPhi(2), start, map, m);
+
+  Node* zero = graph()->NewNode(common()->Int32Constant(0));
+  Node* ret = graph()->NewNode(common()->Return(), zero, phi, ephi1, start);
+  Node* end = graph()->NewNode(common()->End(1), ret);
+
+  graph()->SetEnd(end);
+
+  LinearScheduler simple_scheduler(zone(), graph());
+  EXPECT_TRUE(simple_scheduler.SameBasicBlock(map, f));
+  EXPECT_FALSE(simple_scheduler.SameBasicBlock(map, br1));
+  EXPECT_TRUE(simple_scheduler.SameBasicBlock(ephi1, phi));
+}
+
+TARGET_TEST_F(LinearSchedulerTest, LoopedFloatingDiamond) {
+  Node* start = graph()->NewNode(common()->Start(2));
+  graph()->SetStart(start);
+
+  Node* p0 = graph()->NewNode(common()->Parameter(0), start);
+
+  Node* c = graph()->NewNode(common()->Int32Constant(7));
+  Node* loop = graph()->NewNode(common()->Loop(2), start, start);
+  Node* ind = graph()->NewNode(common()->Phi(MachineRepresentation::kTagged, 2),
+                               p0, p0, loop);
+  Node* add = graph()->NewNode(&kIntAdd, ind, c);
+
+  Node* br = graph()->NewNode(common()->Branch(), add, loop);
+  Node* t = graph()->NewNode(common()->IfTrue(), br);
+  Node* f = graph()->NewNode(common()->IfFalse(), br);
+
+  Node* br1 = graph()->NewNode(common()->Branch(), p0, graph()->start());
+  Node* t1 = graph()->NewNode(common()->IfTrue(), br1);
+  Node* f1 = graph()->NewNode(common()->IfFalse(), br1);
+  Node* m1 = graph()->NewNode(common()->Merge(2), t1, f1);
+  Node* phi1 = graph()->NewNode(
+      common()->Phi(MachineRepresentation::kTagged, 2), add, p0, m1);
+
+  loop->ReplaceInput(1, t);    // close loop.
+  ind->ReplaceInput(1, phi1);  // close induction variable.
+
+  Node* zero = graph()->NewNode(common()->Int32Constant(0));
+  Node* ret = graph()->NewNode(common()->Return(), zero, ind, start, f);
+  Node* end = graph()->NewNode(common()->End(2), ret, f);
+
+  graph()->SetEnd(end);
+
+  LinearScheduler simple_scheduler(zone(), graph());
+  EXPECT_TRUE(simple_scheduler.SameBasicBlock(ind, loop));
+  EXPECT_TRUE(simple_scheduler.SameBasicBlock(phi1, m1));
+  EXPECT_FALSE(simple_scheduler.SameBasicBlock(loop, m1));
+}
+
+}  // namespace compiler
+}  // namespace internal
+}  // namespace v8