Revert of [arm64] A shift of 0 is not allowed in ubfx. (patchset #2 id:20001...

Revert of [arm64] A shift of 0 is not allowed in ubfx. (patchset #2 id:20001 of https://codereview.chromium.org/2685943003/ )

Reason for revert:
Reverting due to causing Word64AndWithImmediateWithWord64Sh to fail locally (but not on the bot).

BUG=v8:5956

Original issue's description:
> [arm64] A shift of 0 is not allowed in ubfx.
>
> R=bmeurer@chromium.org, v8-arm-ports@googlegroups.com
> BUG=v8:5951
>
> Review-Url: https://codereview.chromium.org/2685943003
> Cr-Commit-Position: refs/heads/master@{#43090}
> Committed: https://chromium.googlesource.com/v8/v8/+/c46ccef921ee754d60283d132b9d19f64ae7b1ff

TBR=bmeurer@chromium.org,v8-arm-ports@googlegroups.com,martyn.capewell@arm.com,ahaas@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=v8:5951

Review-Url: https://codereview.chromium.org/2687373002
Cr-Commit-Position: refs/heads/master@{#43105}

src/compiler/arm64/instruction-selector-arm64.cc

@@ -957,19 +957,17 @@ void InstructionSelector::VisitWord64And(Node* node) {
         // 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;
-
-          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;
-        }
+        // 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;
       }
       // Other cases fall through to the normal And operation.
     }

test/cctest/compiler/test-run-machops.cc

@@ -6730,14 +6730,6 @@ TEST(Regression5923) {
   }
 }
 
-TEST(Regression5951) {
-  BufferedRawMachineAssemblerTester<int64_t> m(MachineType::Int64());
-  m.Return(m.Word64And(m.Word64Shr(m.Parameter(0), m.Int64Constant(0)),
-                       m.Int64Constant(0xffffffffffffffffl)));
-  int64_t input = 1234;
-  CHECK_EQ(input, m.Call(input));
-}
-
 #endif  // V8_TARGET_ARCH_64_BIT
 
 }  // namespace compiler