[turbofan] Avoid useless sign extension after sign extended load.

test/unittests/compiler/machine-operator-reducer-unittest.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/base/bits.h"
 #include "src/base/division-by-constant.h"
 #include "src/compiler/js-graph.h"
 #include "src/compiler/machine-operator-reducer.h"
 #include "src/compiler/typer.h"
 #include "test/unittests/compiler/graph-unittest.h"
@@ skipping 627 matching lines @@
       Reduction reduction = Reduce(node);
       EXPECT_TRUE(reduction.Changed());
       EXPECT_THAT(reduction.replacement(),
                   IsInt32Constant(base::bits::RotateRight32(x, y)));
     }
   }
 }
 
 
 // -----------------------------------------------------------------------------
+// Word32Sar
+
+
+TEST_F(MachineOperatorReducerTest, Word32SarWithWord32ShlAndLoad) {
+  Node* const p0 = Parameter(0);
+  Node* const p1 = Parameter(1);
+  {
+    Node* const l = graph()->NewNode(machine()->Load(kMachInt8), p0, p1,
+                                     graph()->start(), graph()->start());
+    Reduction const r = Reduce(graph()->NewNode(
+        machine()->Word32Sar(),
+        graph()->NewNode(machine()->Word32Shl(), l, Int32Constant(24)),
+        Int32Constant(24)));
+    ASSERT_TRUE(r.Changed());
+    EXPECT_EQ(l, r.replacement());
+  }
+  {
+    Node* const l = graph()->NewNode(machine()->Load(kMachInt16), p0, p1,
+                                     graph()->start(), graph()->start());
+    Reduction const r = Reduce(graph()->NewNode(
+        machine()->Word32Sar(),
+        graph()->NewNode(machine()->Word32Shl(), l, Int32Constant(16)),
+        Int32Constant(16)));
+    ASSERT_TRUE(r.Changed());
+    EXPECT_EQ(l, r.replacement());
+  }
+}
+
+
+// -----------------------------------------------------------------------------
 // Word32Shl
 
 
 TEST_F(MachineOperatorReducerTest, Word32ShlWithZeroShift) {
   Node* p0 = Parameter(0);
   Node* node = graph()->NewNode(machine()->Word32Shl(), p0, Int32Constant(0));
   Reduction r = Reduce(node);
   ASSERT_TRUE(r.Changed());
   EXPECT_EQ(p0, r.replacement());
 }
@@ skipping 560 matching lines @@
     Reduction r = Reduce(node);
     ASSERT_TRUE(r.Changed());
     EXPECT_THAT(r.replacement(),
                 IsStore(rep, base, index, value, effect, control));
   }
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8