On 2006-12-10, Steve Underwood <[email protected]> wrote:
>>>>I'm having trouble with mspgcc version 3.2.3 accessing a variable
>>>>that's been declared as volatile twice, when my code refers to it
>>>>only once.
>>>>
>>>>
>>[...]
>>
>>>>Note that the code is accessing the switch variable twice, in
>>>>the cmp instruction at 0xfc46 and in the mov instruction at
>>>>0xfc4c. This is fairly problematic, since when I switch on the
>>>>value of I2CIV in my I2C interrupt function I miss a large
>>>>number of interrupts!
>>>>
>>>I'm guessing you weren't optimizing your example code
>>
>>That's moot. The generated code is incorrect[1]. Compilers
>>are not permitted to generate incorrect code regardless of
>>optimization settings.
>>
>>[1] Unless I misunderstood the C standard's requirement for
>> the implementation of volatile variables.
>
> If you turn on optimisation, this problem goes away. As you
> say, that is a moot point if the compiler has produced wrong
> code. I don't know what the C spec actually says, though,
I read it once, but it's a little hard to follow.
> and I don't have a full copy of it to hand. Can anyone quote
> exactly what C99 says on this subject. I suspect GCC has done
> something compliant, but useless.
I'm sure asking on comp.lang.c would get a correct answer.
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