VM: Fix a couple of issues in the AOT optimizer, add fast path smi multiply.

runtime/vm/intermediate_language_x64.cc

Index: runtime/vm/intermediate_language_x64.cc
diff --git a/runtime/vm/intermediate_language_x64.cc b/runtime/vm/intermediate_language_x64.cc
index 1738532b8acfe29782089f7cdfe2583f659b9f05..7e39b45d861db400d65605922a5307b93f5a240e 100644
--- a/runtime/vm/intermediate_language_x64.cc
+++ b/runtime/vm/intermediate_language_x64.cc
@@ -2829,6 +2829,7 @@ LocationSummary* CheckedSmiOpInstr::MakeLocationSummary(Zone* zone,
     case Token::kGTE:
     case Token::kADD:
     case Token::kSUB:
+    case Token::kMUL:
       summary->set_out(0, Location::RequiresRegister());
       break;
     case Token::kBIT_OR:
@@ -2866,6 +2867,12 @@ void CheckedSmiOpInstr::EmitNativeCode(FlowGraphCompiler* compiler) {
       __ subq(result, right);
       __ j(OVERFLOW, slow_path->entry_label());
       break;
+    case Token::kMUL:
+      __ movq(result, left);
+      __ SmiUntag(result);
+      __ imulq(result, right);
+      __ j(OVERFLOW, slow_path->entry_label());
+      break;
     case Token::kBIT_OR:
       ASSERT(left == result);
       __ orq(result, right);