Bug 1825014 part 1 - Assert GetFrameArgument index is in bounds in debug builds. r=iain

  const LAllocation* index = lir->index();

  size_t argvOffset = JitFrameLayout::offsetOfActualArgs();

  // This instruction is used to access actual arguments and formal arguments.

  // The number of Values on the stack is |max(numFormals, numActuals)|, so we

  // assert |index < numFormals || index < numActuals| in debug builds.

  DebugOnly<size_t> numFormals = gen->outerInfo().script()->function()->nargs();

  if (index->isConstant()) {

    int32_t i = index->toConstant()->toInt32();

#ifdef DEBUG

    if (uint32_t(i) >= numFormals) {

      Label ok;

      Register argc = result.scratchReg();

      masm.loadNumActualArgs(FramePointer, argc);

      masm.branch32(Assembler::Above, argc, Imm32(i), &ok);

      masm.assumeUnreachable("Invalid argument index");

      masm.bind(&ok);

    }

#endif

    Address argPtr(FramePointer, sizeof(Value) * i + argvOffset);

    masm.loadValue(argPtr, result);

  } else {

    Register i = ToRegister(index);

#ifdef DEBUG

    Label ok;

    Register argc = result.scratchReg();

    masm.branch32(Assembler::Below, i, Imm32(numFormals), &ok);

    masm.loadNumActualArgs(FramePointer, argc);

    masm.branch32(Assembler::Above, argc, i, &ok);

    masm.assumeUnreachable("Invalid argument index");

    masm.bind(&ok);

#endif

    BaseValueIndex argPtr(FramePointer, i, argvOffset);

    masm.loadValue(argPtr, result);

  }