Bugfix: assert in lithium compile for LMaybeGrowElements

src/crankshaft/mips64/lithium-codegen-mips64.cc

Index: src/crankshaft/mips64/lithium-codegen-mips64.cc
diff --git a/src/crankshaft/mips64/lithium-codegen-mips64.cc b/src/crankshaft/mips64/lithium-codegen-mips64.cc
index d14efafd4d6f55c3ff5cd7d33f50ff40bfbb82b8..55499973150c88d3fee8e48b645ef1981d3d7bec 100644
--- a/src/crankshaft/mips64/lithium-codegen-mips64.cc
+++ b/src/crankshaft/mips64/lithium-codegen-mips64.cc
@@ -4390,7 +4390,15 @@ void LCodeGen::DoDeferredMaybeGrowElements(LMaybeGrowElements* instr) {
 
     LOperand* key = instr->key();
     if (key->IsConstantOperand()) {
-      __ li(a3, Operand(ToSmi(LConstantOperand::cast(key))));
+      LConstantOperand* constant_key = LConstantOperand::cast(key);
+      int32_t int_key = ToInteger32(constant_key);
+      if (Smi::IsValid(int_key)) {
+        __ li(a3, Operand(Smi::FromInt(int_key)));
+      } else {
+        // We should never get here at runtime because there is a smi check on
+        // the key before this point.
+        __ stop("expected smi");
+      }
     } else {
       __ mov(a3, ToRegister(key));
       __ SmiTag(a3);