riscv32 : -mno-strict-align has no effect

[Henri Cloetens]

Hello,

To this regard, again, I read in the "PowerISA_public.v3.0B.pdf" ,
page 25, (quote):

 > Some instructions require their storage operands to
 > have certain alignments. In addition, alignment may
 > affect performance. In general, the best performance is
 > obtained when storage operands are aligned.

This clearly states that for PowerPc, not all memory accesses need to be
aligned. If you want a processor with unaligned access, I would recommend
you to check the different types of PowerPc processors.

Best Regards,

Henri.

On 01/21/2020 09:21 AM, Henri Cloetens wrote:
> Hello,
>
> I dont know why you want to work on a target with unaligned accesses, 
> but there are
> real ones that have this. I am working on a custom processor, and it 
> has it. As far as
> I know - not sure, have to check - there are also other target that 
> have it.
>
> Best Regards,
>
> Henri.
>
>
> On 01/20/2020 11:23 PM, Jim Wilson wrote:
>> On Sun, Jan 19, 2020 at 5:39 PM Alex Rocha Prado <alex.prado@nxp.com> 
>> wrote:
>>> It happens that both line generate the same code, so there is some 
>>> kind of problem with gcc, correct ?
>> -mno-strict-align does have an effect, but it isn't very useful.  The
>> problem here is that gcc knows that the target does not support
>> unaligned accesses, so it is refusing to produce them even when
>> -mno-strict-align is used.  Unfortunately, the only supported target
>> with unaligned accesses is the fake -mtune=size target, which exists
>> only for use with the -Os option.  So if you use -mtune=size
>> -mno-strict-align you can get the result you probably want. However,
>> I wouldn't recommend doing that, as I can't guarantee that -mtune=size
>> will work the same in the future.  If you do have a target that
>> supports unaligned accesses, then you should add support for that
>> target to gcc, and then using -mtune=yourtarget -mno-strict-align will
>> work.  If you don't have a target that supports unaligned accesses,
>> then why do you want the compiler to emit broken code?
>>
>> This alignment stuff should probably be rewritten at some point to
>> make the usage of the options more obvious, but I have no idea when
>> that will happen.  At the moment, there is no incentive, as gcc
>> doesn't have support for any RISC-V targets that support unaligned
>> accesses.
>>
>> Jim
>>
>
>