linux-kernel - Re: [PATCH] ARM: Use udiv/sdiv for __aeabi

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Date:	Fri, 08 Nov 2013 11:04:19 -0800
From:	Stephen Boyd <sboyd@...eaurora.org>
To:	Måns Rullgård <mans@...sr.com>
CC:	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ARM: Use udiv/sdiv for __aeabi_{u}idiv library functions

On 11/08/13 09:02, Måns Rullgård wrote:
> Stephen Boyd <sboyd@...eaurora.org> writes:
>
>> +int __aeabi_idiv(int numerator, int denominator)
>> +{
>> +	if (static_key_false(&cpu_has_idiv)) {
>> +		int ret;
>> +
>> +		asm volatile (
>> +		".arch_extension idiv\n"
>> +		"sdiv %0, %1, %2"
>> +		: "=&r" (ret)
> There is no need for the & in the output constraint.  Dropping it allows
> using one of the source registers as destination which may sometimes be
> beneficial.

Ok. Thanks. That does seem to improve things.

before:

00000000 <__aeabi_idiv>:
   0:   e320f000        nop     {0}
   4:   eafffffe        b       0 <___aeabi_idiv>
   8:   e713f110        sdiv    r3, r0, r1
   c:   e1a00003        mov     r0, r3
  10:   e12fff1e        bx      lr

00000014 <__aeabi_uidiv>:
  14:   e320f000        nop     {0}
  18:   eafffffe        b       0 <___aeabi_uidiv>
  1c:   e733f110        udiv    r3, r0, r1
  20:   e1a00003        mov     r0, r3
  24:   e12fff1e        bx      lr

after:

00000000 <__aeabi_idiv>:
   0:   e320f000        nop     {0}
   4:   eafffffe        b       0 <___aeabi_idiv>
   8:   e710f110        sdiv    r0, r0, r1
   c:   e12fff1e        bx      lr

00000010 <__aeabi_uidiv>:
  10:   e320f000        nop     {0}
  14:   eafffffe        b       0 <___aeabi_uidiv>
  18:   e730f110        udiv    r0, r0, r1
  1c:   e12fff1e        bx      lr


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