Re: [PATCH] gdb/i387-tdep.c: Avoid warning for "-Werror=strict-overflow"

[Pedro Alves <palves at redhat dot com>]

On 10/09/2014 11:05 AM, Walfred Tedeschi wrote:
> Am 10/3/2014 7:49 PM, schrieb Pedro Alves:
>> On 10/03/2014 05:44 PM, Joel Brobecker wrote:
>>>>> Sorry, but obfuscating code to make compilers happy is *not* the way to go.
>>>>>
>>>> OK, I can understand, but for me, these is no other better ways for it,
>>>> except let gdb give up "-Werror" (if always need "--disable-werror"
>>>> during "configure").
>>> I have to agree with Mark on this one, the proposed solution looks
>>> awful. There has to be another way. Maybe declaring a local constant
>>> whose value is I387_XMM0_REGNUM (tdep)?
>> Likely, after transformations and intra-procedural analyses, gcc would
>> end up with the same.
>>
>> This:
>>
>>   for (i = I387_ST0_REGNUM (tdep); i < I387_XMM0_REGNUM (tdep); i++)
>>
>> always iterates exactly 16 times, because I387_XMM0_REGNUM
>> is defined like:
>>
>>   #define I387_XMM0_REGNUM(tdep) (I387_ST0_REGNUM (tdep) + 16)
>>
>> An alternative I think might work would be to give that magic
>> 16 constant a name, say:
>>
>>   #define I387_NUM_ST_REGS 16
>>
>> and then do:
>>
>>   for (i = 0; i < i < I387_NUM_ST_REGS; i++)
>>     {
>>        int r = I387_ST0_REGNUM (tdep) + i;
>>
>>        ... use 'r' instead of 'i' ...
>>     }
>>
>> Thanks,
>> Pedro Alves
>>
> Later on we have introduced the _END macros, as can be seen on i387-tdep.h.
> Creating one or two of them migh be a good idea to homogeinize the way 
> we handle the registers.
> 
> This will finally also join together all ideas presented before in only one.
> 
> Using the end will then make
> 
> for (i = I387_ST0_REGNUM (tdep); i < I387_XMM0_REGNUM (tdep); i++)
> 
> to be
> 
> for (i = I387_ST0_REGNUM (tdep); i < I387_STEND_REGNUM (tdep); i++)
> 
> 
> We also define the number of regs for every technology in that file.

I'm imagining I387_STEND_REGNUM to be just one of:

  #define I387_STEND_REGNUM(tdep) (I387_ST0_REGNUM (tdep) + 16)
  #define I387_STEND_REGNUM(tdep) (I387_ST0_REGNUM (tdep) + I387_NUM_ST_REGS)

Thus exactly the same as I387_XMM0_REGNUM:

  #define I387_XMM0_REGNUM(tdep) (I387_ST0_REGNUM (tdep) + 16)

And so it would trigger the same GCC warning.

So we'd still need to do the local variable trick:

  end = I387_STEND_REGNUM (tdep);
  for (i = I387_ST0_REGNUM (tdep); i < end; i++)

Thanks,
Pedro Alves