[turbofan] Replace shr of masked bits with zero

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/base/ieee754.h"
 #include "src/codegen.h"
@@ skipping 135 matching lines @@
       if (m.left().IsWord32Xor() && m.right().Is(-1)) {
         Int32BinopMatcher mleft(m.left().node());
         if (mleft.right().Is(-1)) {  // (x ^ -1) ^ -1 => x
           return Replace(mleft.left().node());
         }
       }
       break;
     }
     case IrOpcode::kWord32Shl:
       return ReduceWord32Shl(node);
-    case IrOpcode::kWord32Shr: {
-      Uint32BinopMatcher m(node);
-      if (m.right().Is(0)) return Replace(m.left().node());  // x >>> 0 => x
-      if (m.IsFoldable()) {                                  // K >>> K => K
-        return ReplaceInt32(m.left().Value() >> m.right().Value());
-      }
-      return ReduceWord32Shifts(node);
-    }
+    case IrOpcode::kWord32Shr:
+      return ReduceWord32Shr(node);
     case IrOpcode::kWord32Sar:
       return ReduceWord32Sar(node);
     case IrOpcode::kWord32Ror: {
       Int32BinopMatcher m(node);
       if (m.right().Is(0)) return Replace(m.left().node());  // x ror 0 => x
       if (m.IsFoldable()) {                                  // K ror K => K
         return ReplaceInt32(
             base::bits::RotateRight32(m.left().Value(), m.right().Value()));
       }
       break;
@@ skipping 634 matching lines @@
                            Uint32Constant(~((1U << m.right().Value()) - 1U)));
         NodeProperties::ChangeOp(node, machine()->Word32And());
         Reduction reduction = ReduceWord32And(node);
         return reduction.Changed() ? reduction : Changed(node);
       }
     }
   }
   return ReduceWord32Shifts(node);
 }
 
+Reduction MachineOperatorReducer::ReduceWord32Shr(Node* node) {
+  Uint32BinopMatcher m(node);
+  if (m.right().Is(0)) return Replace(m.left().node());  // x >>> 0 => x
+  if (m.IsFoldable()) {                                  // K >>> K => K
+    return ReplaceInt32(m.left().Value() >> m.right().Value());
+  }
+  if (m.left().IsWord32And() && m.right().HasValue()) {
+    Uint32BinopMatcher mleft(m.left().node());
+    if (mleft.right().HasValue()) {
+      uint32_t shift = m.right().Value() & 0x1f;
+      uint32_t mask = mleft.right().Value();
+      if ((mask >> shift) == 0) {
+        // (m >>> s) == 0 implies ((x & m) >>> s) == 0
+        return ReplaceInt32(0);
+      }
+    }
+  }
+  return ReduceWord32Shifts(node);
+}
 
 Reduction MachineOperatorReducer::ReduceWord32Sar(Node* node) {
   Int32BinopMatcher m(node);
   if (m.right().Is(0)) return Replace(m.left().node());  // x >> 0 => x
   if (m.IsFoldable()) {                                  // K >> K => K
     return ReplaceInt32(m.left().Value() >> m.right().Value());
   }
   if (m.left().IsWord32Shl()) {
     Int32BinopMatcher mleft(m.left().node());
     if (mleft.left().IsComparison()) {
@@ skipping 274 matching lines @@
 MachineOperatorBuilder* MachineOperatorReducer::machine() const {
   return jsgraph()->machine();
 }
 
 
 Graph* MachineOperatorReducer::graph() const { return jsgraph()->graph(); }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8