Replace manual untagging of smi with proper Smi methods

runtime/vm/intermediate_language_ia32.cc

Index: runtime/vm/intermediate_language_ia32.cc
diff --git a/runtime/vm/intermediate_language_ia32.cc b/runtime/vm/intermediate_language_ia32.cc
index 1ee8f707340a455c8bfe7334c5cb08d0796022e0..f67900c7885b2a7b8d29ba35a62522b5d2c6a6c8 100644
--- a/runtime/vm/intermediate_language_ia32.cc
+++ b/runtime/vm/intermediate_language_ia32.cc
@@ -6083,8 +6083,7 @@ void ShiftMintOpInstr::EmitNativeCode(FlowGraphCompiler* compiler) {
   if (locs()->in(1).IsConstant()) {
     // Code for a constant shift amount.
     ASSERT(locs()->in(1).constant().IsSmi());
-    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: {