This is the mail archive of the gcc@gcc.gnu.org mailing list for the GCC project.

Index Nav:	[Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav:	[Date Prev] [Date Next]	[Thread Prev] [Thread Next]
Other format:	[Raw text]

Re: Suboptimal code generated for _Bool

From: Andi Kleen <ak at muc dot de>
To: "Marcin 'Qrczak' Kowalczyk" <qrczak at knm dot org dot pl>
Cc: gcc at gcc dot gnu dot org
Date: Sun, 20 Jun 2004 22:27:13 +0200
Subject: Re: Suboptimal code generated for _Bool
References: <1087726447.12404.51.camel@qrnik> <1087734119.9628.3.camel@qrnik>

Marcin 'Qrczak' Kowalczyk <qrczak@knm.org.pl> writes:

> .L4:
>         testb   %dl, %dl
>         jne     .L3
>         xorl    %eax, %eax
> .L3:
>         rep ; ret
>
> BTW, what is the "rep ; ret" in the last line?

That works around a limitation in the Athlon branch predictor.
In some cases it cannot predict a branch to ret, and adding the prefix
avoids that.

-Andi

References:
- Suboptimal code generated for _Bool
  - From: Marcin 'Qrczak' Kowalczyk
- Re: Suboptimal code generated for _Bool
  - From: Marcin 'Qrczak' Kowalczyk

Index Nav:	[Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav:	[Date Prev] [Date Next]	[Thread Prev] [Thread Next]