Revert of [arm64] A shift of 0 is not allowed in ubfx.

src/compiler/arm64/instruction-selector-arm64.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/instruction-selector-impl.h"
 #include "src/compiler/node-matchers.h"
 #include "src/compiler/node-properties.h"
 
 namespace v8 {
 namespace internal {
@@ skipping 939 matching lines @@
       // The mask must be contiguous, and occupy the least-significant bits.
       DCHECK_EQ(0u, base::bits::CountTrailingZeros64(mask));
 
       // Select Ubfx for And(Shr(x, imm), mask) where the mask is in the least
       // significant bits.
       Int64BinopMatcher mleft(m.left().node());
       if (mleft.right().HasValue()) {
         // Any shift value can match; int64 shifts use `value % 64`.
         uint32_t lsb = static_cast<uint32_t>(mleft.right().Value() & 0x3f);
 
-        if (lsb != 0) {
-          // Ubfx cannot extract bits past the register size, however since
-          // shifting the original value would have introduced some zeros we can
-          // still use ubfx with a smaller mask and the remaining bits will be
-          // zeros.
-          if (lsb + mask_width > 64) mask_width = 64 - lsb;
+        // Ubfx cannot extract bits past the register size, however since
+        // shifting the original value would have introduced some zeros we can
+        // still use ubfx with a smaller mask and the remaining bits will be
+        // zeros.
+        if (lsb + mask_width > 64) mask_width = 64 - lsb;
 
-          Emit(kArm64Ubfx, g.DefineAsRegister(node),
-               g.UseRegister(mleft.left().node()),
-               g.UseImmediateOrTemp(mleft.right().node(), lsb),
-               g.TempImmediate(static_cast<int32_t>(mask_width)));
-          return;
-        }
+        Emit(kArm64Ubfx, g.DefineAsRegister(node),
+             g.UseRegister(mleft.left().node()),
+             g.UseImmediateOrTemp(mleft.right().node(), lsb),
+             g.TempImmediate(static_cast<int32_t>(mask_width)));
+        return;
       }
       // Other cases fall through to the normal And operation.
     }
   }
   VisitLogical<Int64BinopMatcher>(
       this, node, &m, kArm64And, CanCover(node, m.left().node()),
       CanCover(node, m.right().node()), kLogical64Imm);
 }
 
 
@@ skipping 1729 matching lines @@
 // static
 MachineOperatorBuilder::AlignmentRequirements
 InstructionSelector::AlignmentRequirements() {
   return MachineOperatorBuilder::AlignmentRequirements::
       FullUnalignedAccessSupport();
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8