Fix test Regression6046b.

src/compiler/mips/instruction-selector-mips.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/adapters.h"
 #include "src/base/bits.h"
 #include "src/compiler/instruction-selector-impl.h"
 #include "src/compiler/node-matchers.h"
 #include "src/compiler/node-properties.h"
 
@@ skipping 480 matching lines @@
   }
   VisitRRO(this, kMipsShl, node);
 }
 
 
 void InstructionSelector::VisitWord32Shr(Node* node) {
   Int32BinopMatcher m(node);
   if (m.left().IsWord32And() && m.right().HasValue()) {
     uint32_t lsb = m.right().Value() & 0x1f;
     Int32BinopMatcher mleft(m.left().node());
-    if (mleft.right().HasValue()) {
+    if (mleft.right().HasValue() && mleft.right().Value() != 0) {
       // Select Ext for Shr(And(x, mask), imm) where the result of the mask is
       // shifted into the least-significant bits.
       uint32_t mask = (mleft.right().Value() >> lsb) << lsb;
       unsigned mask_width = base::bits::CountPopulation32(mask);
       unsigned mask_msb = base::bits::CountLeadingZeros32(mask);
       if ((mask_msb + mask_width + lsb) == 32) {
         MipsOperandGenerator g(this);
         DCHECK_EQ(lsb, base::bits::CountTrailingZeros32(mask));
         Emit(kMipsExt, g.DefineAsRegister(node),
              g.UseRegister(mleft.left().node()), g.TempImmediate(lsb),
@@ skipping 1414 matching lines @@
     DCHECK(IsMipsArchVariant(kLoongson) || IsMipsArchVariant(kMips32r1) ||
            IsMipsArchVariant(kMips32r2));
     return MachineOperatorBuilder::AlignmentRequirements::
         NoUnalignedAccessSupport();
   }
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8