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

runtime/vm/intermediate_language_mips.cc

Index: runtime/vm/intermediate_language_mips.cc
diff --git a/runtime/vm/intermediate_language_mips.cc b/runtime/vm/intermediate_language_mips.cc
index 7342fb698f6d42b1d7d01eee8f7d4a6afed788b4..b34ac4cc2e91e6b3a8ffea1a3c24eb4486f200ac 100644
--- a/runtime/vm/intermediate_language_mips.cc
+++ b/runtime/vm/intermediate_language_mips.cc
@@ -2940,6 +2940,14 @@ void CheckedSmiOpInstr::EmitNativeCode(FlowGraphCompiler* compiler) {
       __ SubuDetectOverflow(result, left, right, CMPRES1);
       __ bltz(CMPRES1, slow_path->entry_label());
       break;
+    case Token::kMUL:
+      __ sra(TMP, left, kSmiTagSize);
+      __ mult(TMP, right);
+      __ mflo(result);
+      __ mfhi(CMPRES2);
+      __ sra(CMPRES1, result, 31);
+      __ bne(CMPRES1, CMPRES2, slow_path->entry_label());
+      break;
     case Token::kBIT_OR:
       // Operation part of combined smi check.
       break;