Fix Smi::IsValid assert in StringCharCodeAt deferred code.

src/arm/lithium-codegen-arm.cc

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 2869 matching lines @@
   Register result = ToRegister(instr->result());
   Register scratch = scratch0();
 
   // TODO(3095996): Get rid of this. For now, we need to make the
   // result register contain a valid pointer because it is already
   // contained in the register pointer map.
   __ mov(result, Operand(0));
 
   __ PushSafepointRegisters();
   __ push(string);
-  // Push the index as a smi.
+  // Push the index as a smi. It's safe because this instruction must
+  // be dominated by a bounds check and because of the assert.
+  STATIC_ASSERT(String::kMaxLength <= Smi::kMaxValue);
   if (instr->index()->IsConstantOperand()) {
     int const_index = ToInteger32(LConstantOperand::cast(instr->index()));
+    if (!Smi::IsValid(const_index)) {
+      // Guaranteed to be out of bounds, so we can use "-1" to have a
+      // valid smi.
+      const_index = -1;
+    }
     __ mov(scratch, Operand(Smi::FromInt(const_index)));
     __ push(scratch);
   } else {
     Register index = ToRegister(instr->index());
     __ SmiTag(index);
     __ push(index);
   }
   __ CallRuntimeSaveDoubles(Runtime::kStringCharCodeAt);
   RecordSafepointWithRegisters(
       instr->pointer_map(), 2, Safepoint::kNoDeoptimizationIndex);
@@ skipping 698 matching lines @@
 
 
 void LCodeGen::DoOsrEntry(LOsrEntry* instr) {
   Abort("DoOsrEntry unimplemented.");
 }
 
 
 #undef __
 
 } }  // namespace v8::internal