Add Crankshaft support for smi-only elements

src/x64/lithium-codegen-x64.cc

Index: src/x64/lithium-codegen-x64.cc
diff --git a/src/x64/lithium-codegen-x64.cc b/src/x64/lithium-codegen-x64.cc
index e000feff1d2fcad336ddd1805698286df3018c1a..0bcfd2335abcd72c8069577d63bc22cca5b31ba9 100644
--- a/src/x64/lithium-codegen-x64.cc
+++ b/src/x64/lithium-codegen-x64.cc
@@ -3158,6 +3158,13 @@ void LCodeGen::DoStoreKeyedFastElement(LStoreKeyedFastElement* instr) {
   Register elements = ToRegister(instr->object());
   Register key = instr->key()->IsRegister() ? ToRegister(instr->key()) : no_reg;
 
+  // This instruction cannot handle the FAST_SMI_ONLY_ELEMENTS -> FAST_ELEMENTS
+  // conversion, so it deopts in that case.
+  if (instr->hydrogen()->ValueNeedsSmiCheck()) {
+    Condition cc = masm()->CheckSmi(value);
+    DeoptimizeIf(NegateCondition(cc), instr->environment());
+  }
+
   // Do the store.
   if (instr->key()->IsConstantOperand()) {
     ASSERT(!instr->hydrogen()->NeedsWriteBarrier());