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Date: Wed, 22 Apr 2020 16:29:19 +1000
From: Nicholas Piggin <npiggin@...il.com>
To: Rich Felker <dalias@...c.org>
Cc: Adhemerval Zanella <adhemerval.zanella@...aro.org>,
libc-alpha@...rceware.org, libc-dev@...ts.llvm.org,
linuxppc-dev@...ts.ozlabs.org, musl@...ts.openwall.com
Subject: Re: Powerpc Linux 'scv' system call ABI proposal take 2
Excerpts from Nicholas Piggin's message of April 22, 2020 4:18 pm:
> If we go further and try to preserve r3 as well by putting the return
> value in r9 or r0, we go backwards about 300 bytes. It's good for the
> lock loops and complex functions, but hurts a lot of simpler functions
> that have to add 'mr r3,r9' etc.
>
> Most of the time there are saved non-volatile GPRs around anyway though,
> so not sure which way to go on this. Text size savings can't be ignored
> and it's pretty easy for the kernel to do (we already save r3-r8 and
> zero them on exit, so we could load them instead from cache line that's
> should be hot).
>
> So I may be inclined to go this way, even if we won't see benefit now.
By, "this way" I don't mean r9 or r0 return value (which is larger code),
but r3 return value with r0,r4-r8 preserved.
Thanks,
Nick
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