Re: [PATCH v2] Implement new RTL optimizations pass: fold-mem-offsets.

[Jeff Law <jeffreyalaw@gmail.com>]

On 7/12/23 03:12, Manolis Tsamis wrote:
> On Mon, Jul 10, 2023 at 12:58 AM Hans-Peter Nilsson <hp@bitrange.com> wrote:
>>
>> On Sun, 9 Jul 2023, Hans-Peter Nilsson wrote:
>>
>>> On Thu, 15 Jun 2023, Manolis Tsamis wrote:
>>>
>>>> This is a new RTL pass that tries to optimize memory offset calculations
>>>> by moving them from add immediate instructions to the memory loads/stores.
>>
>>> It punts on all "use" insns that are not SET.
>>> Why not use single_set there too?
>>
>> Also, I don't see insn costs considered?
>> (Also: typo "immidiate".)
>>
> 
> The only change that this pass does is to change offsets where
> possible and then simplify add immediate instructions to register
> moves.
> I don't see how this could result in worse performance and by
> extension I don't see where insn costs could be used.
> Do you have any thoughts about where to use the costs?
If the offset crosses an architectural size boundary such that the 
instruction was longer, but still valid, it could affect the cost.

That's the most obvious case to me.  There may be others.

Any progress on that m68k issue?  I've also got a report of x264 failing 
to build on riscv64 with the V2 variant, but I haven't distilled that 
down to a testcase yet.

jeff