Skip site navigation (1) Skip section navigation (2)

Re: fix for strict-alias warnings

From: Manfred Spraul <manfred(at)colorfullife(dot)com>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Andrew Dunstan <andrew(at)dunslane(dot)net>,"Patches (PostgreSQL)" <pgsql-patches(at)postgresql(dot)org>
Subject: Re: fix for strict-alias warnings
Date: 2003-10-14 21:01:14
Message-ID: 3F8C641A.2010700@colorfullife.com (view raw or flat)
Thread:
Lists: pgsql-hackerspgsql-patches
Tom Lane wrote:

>Manfred Spraul <manfred(at)colorfullife(dot)com> writes:
>  
>
>>After some massaging, I've succeeded in generating bad code using a 
>>slightly modified MemSetAligned macro (parameters -O2 
>>-fstrict-aliasing): gcc pipelined the x*x around the memset.
>>    
>>
>
>As I already explained, we do not care about the MemSetAligned case.
>Is gcc 3.3 smart enough to optimize away the pointer alignment test
>in the full macro?
>
3.2 optimizes away the pointer alignment test, but then doesn't pipeline 
the "x*x" calculation. It might be due to a known (and now fixed) bug in 
gcc where is lost track of constants, and thus didn't succeed in 
optimizing long calculations.

I don't have gcc 3.3 installed, but IMHO it would be insane to leave 
strict alias analysis enabled - writing to *(int32*)addr violates the 
alias rules, the bad code generated with MemSetAligned proved that.
Is someone around with 3.3 who could test MemSet?

--
    Manfred



In response to

Responses

pgsql-hackers by date

Next:From: Jon JensenDate: 2003-10-14 21:04:45
Subject: Re: postgres --help-config
Previous:From: Peter EisentrautDate: 2003-10-14 20:45:17
Subject: Re: fix for strict-alias warnings

pgsql-patches by date

Next:From: Ian BarwickDate: 2003-10-14 21:14:48
Subject: psql tab completion bug and possible fix
Previous:From: Peter EisentrautDate: 2003-10-14 20:45:17
Subject: Re: fix for strict-alias warnings

Privacy Policy | About PostgreSQL
Copyright © 1996-2014 The PostgreSQL Global Development Group