[vm, compiler] Don't clobber non-writable inputs in BinarySmiOp(>>>).

TEST=ci
Bug: https://github.com/dart-lang/sdk/issues/46797
Change-Id: Ia9494ddc1d39b83e2572b8b5a7f208da2540ccd1
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/210501
Reviewed-by: Alexander Markov <alexmarkov@google.com>
Commit-Queue: Ryan Macnak <rmacnak@google.com>

runtime/tests/vm/dart/regress_46797_test.dart

@@ -0,0 +1,21 @@
+// Copyright (c) 2021, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// VMOptions=--optimization-counter-threshold=100
+
+int var74 = -43;
+
+@pragma("vm:never-inline")
+foo(int var74) {
+  if (var74 >>> 0xC == 675872701) {
+    print("side-effect");
+  }
+}
+
+main() {
+  for (var i = 0; i < 200; i++) {
+    foo(43);
+  }
+  foo(-43);
+}

runtime/vm/compiler/backend/il_arm64.cc

@@ -3541,8 +3541,8 @@ void BinarySmiOpInstr::EmitNativeCode(FlowGraphCompiler* compiler) {
         const intptr_t kCountLimit = 0x3F;
         intptr_t value = Smi::Cast(constant).Value();
         ASSERT((value >= 0) && (value <= kCountLimit));
-        __ SmiUntag(left);
-        __ LsrImmediate(result, left, value);
+        __ SmiUntag(result, left);
+        __ LsrImmediate(result, result, value);
         if (deopt != nullptr) {
           __ SmiTagAndBranchIfOverflow(result, deopt);
         } else {