Re: [PATCH] Enable shrink wrapping for the RISC-V target.

[Palmer Dabbelt <palmer@dabbelt.com>]

On Wed, 02 Nov 2022 08:06:36 PDT (-0700), jlaw@ventanamicro.com wrote:
>
> On 11/2/22 07:54, Manolis Tsamis wrote:
>>
>> I've revisited this testcase and I think it's not possible to make it
>> work with the current implementation.
>> It's not possible to trigger shrink wrapping in this case since the
>> wrapping of registers is guarded by
>>   if (SMALL_OPERAND (offset)) { bitmap_set_bit (components, regno); }
>> Hence if a long stack is generated we get no shrink wrapping.

Ah, sorry, I must have just missed that when reading the code.  In that 
case we're essentailly just doing what the other port was, so we're 
safe.

>> I also tried to remove that restriction but it looks like it can't
>> work because we can't create
>> pseudo-registers during shrink wrapping and shrink wrapping can't work either.
>>
>> I believe this means that shrink wrapping cannot interfere with a long
>> stack frame
>> so there is nothing to test against in this case?
>
> It'd be marginally better to have such a test case to ensure we don't
> shrink wrap it -- that would ensure that someone doesn't accidentally
> introduce shrink wrapping with large offsets.   Just a bit of future
> proofing.

If there's passing test cases that fail with that check removed then 
it's probably good enough, though I think in this case just having a 
comment there saying why the short-stack check is necessary should be 
fine.