Replace manual untagging of smi with proper Smi methods

runtime/vm/intermediate_language_arm.cc

Index: runtime/vm/intermediate_language_arm.cc
diff --git a/runtime/vm/intermediate_language_arm.cc b/runtime/vm/intermediate_language_arm.cc
index 995c1cd866cb947eb2d25850a61dac94d9bcb201..7af5dade7f23147802be7d8574e418bc6bf78877 100644
--- a/runtime/vm/intermediate_language_arm.cc
+++ b/runtime/vm/intermediate_language_arm.cc
@@ -6544,8 +6544,7 @@ void ShiftMintOpInstr::EmitNativeCode(FlowGraphCompiler* compiler) {
   if (locs()->in(1).IsConstant()) {
     // Code for a constant shift amount.
     ASSERT(locs()->in(1).constant().IsSmi());

[Vyacheslav Egorov (Google), 2017/07/12 16:56:27]

I think this ASSERT can be deleted because Smi::Cast(...) contains the same
assert.

[alexmarkov, 2017/07/12 17:37:37]

You are right, it can be deleted. However, I think the explicit ASSERT makes
this code a little bit more readable. Also, it is more convenient to get an
assertion failure message at a more specific place rather than inside generic
Smi::Cast() which is called from many other places.

So I would prefer to leave it here, if you don't mind.

-    const int32_t shift =
-        reinterpret_cast<int32_t>(locs()->in(1).constant().raw()) >> 1;
+    const int32_t shift = Smi::Cast(locs()->in(1).constant()).Value();
     ASSERT(shift >= 0);
     switch (op_kind()) {
       case Token::kSHR: {