[turbofan] Canonicalize x - K to x + -K.

src/compiler/machine-operator-reducer.cc

 // 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/machine-operator-reducer.h"
 
 #include "src/base/bits.h"
 #include "src/base/division-by-constant.h"
 #include "src/codegen.h"
 #include "src/compiler/diamond.h"
@@ skipping 57 matching lines @@
 
 
 Node* MachineOperatorReducer::Int32Add(Node* lhs, Node* rhs) {
   Node* const node = graph()->NewNode(machine()->Int32Add(), lhs, rhs);
   Reduction const reduction = ReduceInt32Add(node);
   return reduction.Changed() ? reduction.replacement() : node;
 }
 
 
 Node* MachineOperatorReducer::Int32Sub(Node* lhs, Node* rhs) {
-  return graph()->NewNode(machine()->Int32Sub(), lhs, rhs);
+  Node* const node = graph()->NewNode(machine()->Int32Sub(), lhs, rhs);
+  Reduction const reduction = ReduceInt32Sub(node);
+  return reduction.Changed() ? reduction.replacement() : node;
 }
 
 
 Node* MachineOperatorReducer::Int32Mul(Node* lhs, Node* rhs) {
   return graph()->NewNode(machine()->Int32Mul(), lhs, rhs);
 }
 
 
 Node* MachineOperatorReducer::Int32Div(Node* dividend, int32_t divisor) {
   DCHECK_NE(0, divisor);
@@ skipping 120 matching lines @@
         node->ReplaceInput(0, msub.left().node());
         node->ReplaceInput(1, msub.right().node());
         return Changed(node);
       }
       // TODO(turbofan): fold HeapConstant, ExternalReference, pointer compares
       if (m.LeftEqualsRight()) return ReplaceBool(true);  // x == x => true
       break;
     }
     case IrOpcode::kInt32Add:
       return ReduceInt32Add(node);
-    case IrOpcode::kInt32Sub: {
-      Int32BinopMatcher m(node);
-      if (m.right().Is(0)) return Replace(m.left().node());  // x - 0 => x
-      if (m.IsFoldable()) {                                  // K - K => K
-        return ReplaceInt32(static_cast<uint32_t>(m.left().Value()) -
-                            static_cast<uint32_t>(m.right().Value()));
-      }
-      if (m.LeftEqualsRight()) return ReplaceInt32(0);  // x - x => 0
-      break;
-    }
+    case IrOpcode::kInt32Sub:
+      return ReduceInt32Sub(node);
     case IrOpcode::kInt32Mul: {
       Int32BinopMatcher m(node);
       if (m.right().Is(0)) return Replace(m.right().node());  // x * 0 => 0
       if (m.right().Is(1)) return Replace(m.left().node());   // x * 1 => x
       if (m.IsFoldable()) {                                   // K * K => K
         return ReplaceInt32(m.left().Value() * m.right().Value());
       }
       if (m.right().Is(-1)) {  // x * -1 => 0 - x
         node->set_op(machine()->Int32Sub());
         node->ReplaceInput(0, Int32Constant(0));
@@ skipping 229 matching lines @@
   Int32BinopMatcher m(node);
   if (m.right().Is(0)) return Replace(m.left().node());  // x + 0 => x
   if (m.IsFoldable()) {                                  // K + K => K
     return ReplaceUint32(bit_cast<uint32_t>(m.left().Value()) +
                          bit_cast<uint32_t>(m.right().Value()));
   }
   return NoChange();
 }
 
 
+Reduction MachineOperatorReducer::ReduceInt32Sub(Node* node) {
+  DCHECK_EQ(IrOpcode::kInt32Sub, node->opcode());
+  Int32BinopMatcher m(node);
+  if (m.right().Is(0)) return Replace(m.left().node());  // x - 0 => x
+  if (m.IsFoldable()) {                                  // K - K => K
+    return ReplaceInt32(static_cast<uint32_t>(m.left().Value()) -
+                        static_cast<uint32_t>(m.right().Value()));
+  }
+  if (m.LeftEqualsRight()) return ReplaceInt32(0);  // x - x => 0
+  if (m.right().HasValue()) {                       // x - K => x + -K
+    node->set_op(machine()->Int32Add());
+    node->ReplaceInput(1, Int32Constant(-m.right().Value()));
+    Reduction const reduction = ReduceInt32Add(node);
+    return reduction.Changed() ? reduction : Changed(node);
+  }
+  return NoChange();
+}
+
+
 Reduction MachineOperatorReducer::ReduceInt32Div(Node* node) {
   Int32BinopMatcher m(node);
   if (m.left().Is(0)) return Replace(m.left().node());    // 0 / x => 0
   if (m.right().Is(0)) return Replace(m.right().node());  // x / 0 => 0
   if (m.right().Is(1)) return Replace(m.left().node());   // x / 1 => x
   if (m.IsFoldable()) {                                   // K / K => K
     return ReplaceInt32(
         base::bits::SignedDiv32(m.left().Value(), m.right().Value()));
   }
   if (m.LeftEqualsRight()) {  // x / x => x != 0
@@ skipping 425 matching lines @@
 MachineOperatorBuilder* MachineOperatorReducer::machine() const {
   return jsgraph()->machine();
 }
 
 
 Graph* MachineOperatorReducer::graph() const { return jsgraph()->graph(); }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8