[turbofan] Optimize Int32Mod by power-of-two.

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/codegen.h"
 #include "src/compiler/generic-node-inl.h"
 #include "src/compiler/graph.h"
@@ skipping 244 matching lines @@
       if (m.IsFoldable() && !m.right().Is(0)) {  // K / K => K
         return ReplaceInt32(m.left().Value() / m.right().Value());
       }
       if (m.right().IsPowerOf2()) {  // x / 2^n => x >> n
         node->set_op(machine()->Word32Shr());
         node->ReplaceInput(1, Int32Constant(WhichPowerOf2(m.right().Value())));
         return Changed(node);
       }
       break;
     }
-    case IrOpcode::kInt32Mod: {
-      Int32BinopMatcher m(node);
-      if (m.right().Is(1)) return ReplaceInt32(0);   // x % 1  => 0
-      if (m.right().Is(-1)) return ReplaceInt32(0);  // x % -1 => 0
-      // TODO(turbofan): if (m.left().Is(0))
-      // TODO(turbofan): if (m.right().IsPowerOf2())
-      // TODO(turbofan): if (m.right().Is(0))
-      // TODO(turbofan): if (m.LeftEqualsRight())
-      if (m.IsFoldable() && !m.right().Is(0)) {  // K % K => K
-        return ReplaceInt32(m.left().Value() % m.right().Value());
-      }
-      break;
-    }
+    case IrOpcode::kInt32Mod:
+      return ReduceInt32Mod(node);
     case IrOpcode::kUint32Mod: {
       Uint32BinopMatcher m(node);
       if (m.right().Is(1)) return ReplaceInt32(0);  // x % 1 => 0
       // TODO(turbofan): if (m.left().Is(0))
       // TODO(turbofan): if (m.right().Is(0))
       // TODO(turbofan): if (m.LeftEqualsRight())
       if (m.IsFoldable() && !m.right().Is(0)) {  // K % K => K
         return ReplaceInt32(m.left().Value() % m.right().Value());
       }
       if (m.right().IsPowerOf2()) {  // x % 2^n => x & 2^n-1
@@ skipping 215 matching lines @@
       }
       break;
     }
     default:
       break;
   }
   return NoChange();
 }
 
 
+Reduction MachineOperatorReducer::ReduceInt32Mod(Node* const node) {
+  Int32BinopMatcher m(node);
+  if (m.right().Is(1)) return ReplaceInt32(0);   // x % 1  => 0
+  if (m.right().Is(-1)) return ReplaceInt32(0);  // x % -1 => 0
+  // TODO(turbofan): if (m.left().Is(0))
+  // TODO(turbofan): if (m.right().Is(0))
+  // TODO(turbofan): if (m.LeftEqualsRight())
+  if (m.IsFoldable() && !m.right().Is(0)) {  // K % K => K
+    return ReplaceInt32(m.left().Value() % m.right().Value());
+  }
+  if (m.right().IsPowerOf2()) {
+    int32_t const divisor = m.right().Value();
+    Node* zero = Int32Constant(0);
+    Node* mask = Int32Constant(divisor - 1);
+    Node* dividend = m.left().node();
+
+    Node* check = graph()->NewNode(machine()->Int32LessThan(), dividend, zero);
+    Node* branch =
+        graph()->NewNode(common()->Branch(), check, graph()->start());
+
+    Node* if_true = graph()->NewNode(common()->IfTrue(), branch);
+    Node* neg = graph()->NewNode(
+        machine()->Int32Sub(), zero,
+        graph()->NewNode(
+            machine()->Word32And(),
+            graph()->NewNode(machine()->Int32Sub(), zero, dividend), mask));
+
+    Node* if_false = graph()->NewNode(common()->IfFalse(), branch);
+    Node* pos = graph()->NewNode(machine()->Word32And(), dividend, mask);
+
+    Node* merge = graph()->NewNode(common()->Merge(2), if_true, if_false);
+    Node* phi = graph()->NewNode(common()->Phi(kMachInt32, 2), neg, pos, merge);
+    return Replace(phi);
+  }
+  return NoChange();
+}
+
+
 Reduction MachineOperatorReducer::ReduceProjection(size_t index, Node* node) {
   switch (node->opcode()) {
     case IrOpcode::kInt32AddWithOverflow: {
       DCHECK(index == 0 || index == 1);
       Int32BinopMatcher m(node);
       if (m.IsFoldable()) {
         int32_t val;
         bool ovf = base::bits::SignedAddOverflow32(m.left().Value(),
                                                    m.right().Value(), &val);
         return ReplaceInt32((index == 0) ? val : ovf);
@@ skipping 32 matching lines @@
 MachineOperatorBuilder* MachineOperatorReducer::machine() const {
   return jsgraph()->machine();
 }
 
 
 Graph* MachineOperatorReducer::graph() const { return jsgraph()->graph(); }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8