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 2772 matching lines @@
 void LCodeGen::DoStringCharCodeAt(LStringCharCodeAt* instr) {
   class DeferredStringCharCodeAt: public LDeferredCode {
    public:
     DeferredStringCharCodeAt(LCodeGen* codegen, LStringCharCodeAt* instr)
         : LDeferredCode(codegen), instr_(instr) { }
     virtual void Generate() { codegen()->DoDeferredStringCharCodeAt(instr_); }
    private:
     LStringCharCodeAt* instr_;
   };
 
-  DeferredStringCharCodeAt* deferred
-      = new DeferredStringCharCodeAt(this, instr);
-
   Register scratch = scratch0();
   Register string = ToRegister(instr->string());
   Register index = no_reg;
   int const_index = -1;
   if (instr->index()->IsConstantOperand()) {
     const_index = ToInteger32(LConstantOperand::cast(instr->index()));
+    STATIC_ASSERT(String::kMaxLength <= Smi::kMaxValue);
+    if (!Smi::IsValid(const_index)) {
+      // Guaranteed to be out of bounds because of the assert above.
+      // So the bounds check that must dominate this instruction must
+      // have deoptimized already.
+      if (FLAG_debug_code) {
+        __ Abort("StringCharCodeAt: out of bounds index.");
+      }
+      // No code needs to be generated.
+      return;
+    }
   } else {
     index = ToRegister(instr->index());
   }
   Register result = ToRegister(instr->result());
 
+  DeferredStringCharCodeAt* deferred =
+      new DeferredStringCharCodeAt(this, instr);
+
   Label flat_string, ascii_string, done;
 
   // Fetch the instance type of the receiver into result register.
   __ ldr(result, FieldMemOperand(string, HeapObject::kMapOffset));
   __ ldrb(result, FieldMemOperand(result, Map::kInstanceTypeOffset));
 
   // We need special handling for non-flat strings.
   STATIC_ASSERT(kSeqStringTag == 0);
   __ tst(result, Operand(kStringRepresentationMask));
   __ b(eq, &flat_string);
@@ skipping 63 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. This is safe because of the checks in
+  // DoStringCharCodeAt above.
   if (instr->index()->IsConstantOperand()) {
     int const_index = ToInteger32(LConstantOperand::cast(instr->index()));
     __ mov(scratch, Operand(Smi::FromInt(const_index)));
     __ push(scratch);
   } else {
     Register index = ToRegister(instr->index());
     __ SmiTag(index);
     __ push(index);
   }
   __ CallRuntimeSaveDoubles(Runtime::kStringCharCodeAt);
@@ skipping 700 matching lines @@
 
 
 void LCodeGen::DoOsrEntry(LOsrEntry* instr) {
   Abort("DoOsrEntry unimplemented.");
 }
 
 
 #undef __
 
 } }  // namespace v8::internal