From: Dominik Vogt <vogt@linux.vnet.ibm.com>
To: libffi-discuss@sourceware.org
Subject: Re: [PATCH 3/4] s390: Reorganize assembly
Date: Tue, 23 Dec 2014 09:54:00 -0000 [thread overview]
Message-ID: <20141223095439.GA4745@linux.vnet.ibm.com> (raw)
In-Reply-To: <54984712.2050609@redhat.com>
On Mon, Dec 22, 2014 at 08:30:10AM -0800, Richard Henderson wrote:
> On 12/22/2014 04:25 AM, Dominik Vogt wrote:
> > Or rather the attached patch stat replaces
> >
> > stm %r2,%r3,0(%r12)
> > nop
> >
> > with
> >
> > st %r2,0(%r12)
> > st %r3,4(%r12)
>
> Is that really an improvement?
>
> (1) You now need a branch for the (presumed) normal "int" case.
Well, depends on whether we talk about 64 bit or 31 bit:
64 bit
------
+ saves decoding two nop instructions for int64_t
+ saves four bytes
31 bit
------
+ saves decoding two nop instructions for int64_t
- replaces a nop with a jump instruction for int32_t
Of course one could have a different order of types depending on
the platform to eliminate the disadvantage of the 31 bit case.
> (2) Is stm really that much faster than two st? I would have
> thought the reverse, actually.
No, stm+nop is potentially slower than two st. That's why the
patch uses the two st instructions.
P.S.: Just noticed there's a duplicate ".balign" in the patched
code.
Ciao
Dominik ^_^ ^_^
--
Dominik Vogt
IBM Germany
next prev parent reply other threads:[~2014-12-23 9:54 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-12-18 21:33 [PATCH 0/4] s390 improvements Richard Henderson
2014-12-18 21:33 ` [PATCH 1/4] s390: Kill trailing whitespace Richard Henderson
2014-12-18 21:33 ` [PATCH 2/4] s390: Avoid aliasing warnings Richard Henderson
2014-12-18 21:33 ` [PATCH 4/4] s390: Use pc-relative insns in 31-bit mode Richard Henderson
2014-12-18 21:33 ` [PATCH 3/4] s390: Reorganize assembly Richard Henderson
2014-12-22 12:12 ` Dominik Vogt
2014-12-22 12:25 ` Dominik Vogt
2014-12-22 16:30 ` Richard Henderson
2014-12-23 9:54 ` Dominik Vogt [this message]
2014-12-19 15:07 ` [PATCH 0/4] s390 improvements Ulrich Weigand
2014-12-19 15:33 ` Richard Henderson
2014-12-19 16:15 ` Ulrich Weigand
2014-12-19 16:37 ` Richard Henderson
2014-12-19 17:08 ` Ulrich Weigand
2014-12-19 16:43 ` [PATCH 5/4] s390: Inline and tidy ffi_prep_args Richard Henderson
2014-12-22 11:34 ` [PATCH 0/4] s390 improvements Dominik Vogt
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