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From: Roland McGrath <roland@hack.frob.com>
To: Will Newton <will.newton@linaro.org>
Cc: libc-ports@sourceware.org,    Patch Tracking <patches@linaro.org>
Subject: Re: [PATCH, v5] ARM: Add Cortex-A15 optimized NEON and VFP memcpy routines, with IFUNC.
Date: Wed, 01 May 2013 17:01:00 -0000	[thread overview]
Message-ID: <20130501170134.265AC2C096@topped-with-meat.com> (raw)
In-Reply-To: Will Newton's message of  Wednesday, 1 May 2013 16:26:04 +0100 <CANu=DmhgUNKBos95su4qaeMRwWWij_Ss3_GhXjJmJChcMjFruA@mail.gmail.com>

> > If __SOFTFP__ is predefined by the compiler, then the compiler is presuming
> > VFP support anyway.  So you can make this:
> >
> > #ifdef __SOFTFP__
> >         ldr     r1, .Lmemcpy_arm
> >         tst     r0, #HWCAP_ARM_VFP
> >         ldrne   r1, .Lmemcpy_vfp
> > #else
> >         ldr     r1, .Lmemcpy_vfp
> > #endif
> >
> > (and also conditionalize .Lmemcpy_arm, below).
> 
> I'm not sure I follow the logic here, could you elaborate?

I dropped a "not" in my first sentence, which might have been confusing.
The compiler predefines __SOFTFP__ unless it's presuming VFP support.  If
__SOFTFP__ is not defined, then the compiler is already generating code
that effectively presumes HWCAP_ARM_VFP will be set, so you might as well
just elide any code testing it at runtime and statically do whatever you
would do if HWCAP_ARM_VFP were set at runtime.


Thanks,
Roland

  reply	other threads:[~2013-05-01 17:01 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2013-04-30 16:54 Will Newton
2013-04-30 17:08 ` Joseph S. Myers
2013-05-01  9:11   ` Will Newton
2013-04-30 17:18 ` Roland McGrath
2013-05-01 15:26   ` Will Newton
2013-05-01 17:01     ` Roland McGrath [this message]
2013-05-01 18:43       ` Will Newton
2013-05-02 19:54         ` Roland McGrath
2013-05-01 12:53 ` Richard Henderson
2013-05-01 16:50   ` Roland McGrath

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