[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-Original-Commit-Position: refs/heads/master@{#43090}
Committed: https://chromium.googlesource.com/v8/v8/+/c46ccef921ee754d60283d132b9d19f64ae7b1ff
Review-Url: https://codereview.chromium.org/2685943003
Cr-Commit-Position: refs/heads/master@{#43199}

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

@@ -946,7 +946,8 @@ void InstructionSelector::VisitWord64And(Node* node) {
     uint64_t mask = m.right().Value();
     uint64_t mask_width = base::bits::CountPopulation64(mask);
     uint64_t mask_msb = base::bits::CountLeadingZeros64(mask);
-    if ((mask_width != 0) && (mask_msb + mask_width == 64)) {
+    if ((mask_width != 0) && (mask_width != 64) &&
+        (mask_msb + mask_width == 64)) {
       // The mask must be contiguous, and occupy the least-significant bits.
       DCHECK_EQ(0u, base::bits::CountTrailingZeros64(mask));
 

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

@@ -6730,6 +6730,14 @@ 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