RE: [PATCH v3] RISCV: Add -m(no)-omit-leaf-frame-pointer support.

["Wang, Yanzhang" <yanzhang.wang@intel.com>]

Hi Jeff,

Do you have any further comments about this patch ?

Thanks,
Yanzhang

> -----Original Message-----
> From: Jeff Law <jeffreyalaw@gmail.com>
> Sent: Friday, July 21, 2023 12:11 PM
> To: Kito Cheng <kito.cheng@gmail.com>; Wang, Yanzhang
> <yanzhang.wang@intel.com>
> Cc: gcc-patches@gcc.gnu.org; juzhe.zhong@rivai.ai; kito.cheng@sifive.com;
> Li, Pan2 <pan2.li@intel.com>
> Subject: Re: [PATCH v3] RISCV: Add -m(no)-omit-leaf-frame-pointer support.
> 
> 
> 
> On 7/20/23 21:49, Kito Cheng wrote:
> > LGTM, I think long jump is another issue and making ra become a fixed
> > register will escalate to an ABI issue, so that should not be a
> > blocker for this patch.
> I'll take a look tomorrow, but I'm supportive of what Yanzhang is trying to
> do in principle.  I've got a few hot items to deal with tonight though.
> 
> WRT making $ra fixed.  In practice fixing a register just takes it out of
> the pool of things available to the allocator.  Furthermore $ra is always
> considered clobbered at call sites.  So while one could view it as an ABI
> change, it's not one that's actually observable in practice.
> I suspect that's one of the reasons why $ra is used by the assembler in
> this manner -- it minimizes both the ABI and performance impacts.
> 
> jeff