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Re: [PATCH] Fixes tree-loop-distribute-patterns issues
- From: OndÅej BÃlka <neleai at seznam dot cz>
- To: "Joseph S. Myers" <joseph at codesourcery dot com>
- Cc: Roland McGrath <roland at hack dot frob dot com>, Adhemerval Zanella <azanella at linux dot vnet dot ibm dot com>, Carlos O'Donell <carlos at redhat dot com>, "GNU C. Library" <libc-alpha at sourceware dot org>, Siddhesh Poyarekar <siddhesh at redhat dot com>
- Date: Fri, 21 Jun 2013 02:43:38 +0200
- Subject: Re: [PATCH] Fixes tree-loop-distribute-patterns issues
- References: <51C0AFB7 dot 1060009 at linux dot vnet dot ibm dot com> <20130618205608 dot 9CCE22C0AC at topped-with-meat dot com> <51C1BFE9 dot 4070805 at linux dot vnet dot ibm dot com> <51C1CEFC dot 9000100 at redhat dot com> <51C1FE4C dot 3020400 at linux dot vnet dot ibm dot com> <20130619221130 dot 7B91A2C10E at topped-with-meat dot com> <51C31177 dot 90303 at linux dot vnet dot ibm dot com> <20130620175832 dot 0E6FA2C133 at topped-with-meat dot com> <20130620213141 dot GA4833 at domone dot kolej dot mff dot cuni dot cz> <Pine dot LNX dot 4 dot 64 dot 1306202232290 dot 14606 at digraph dot polyomino dot org dot uk>
On Thu, Jun 20, 2013 at 10:33:21PM +0000, Joseph S. Myers wrote:
> On Thu, 20 Jun 2013, Ondrej Bilka wrote:
>
> > Actually you should split simple_* to separate files and compile them with
> > O0.
> >
> > Doing otherwise makes their performance dependent on gcc version and
> > this makes results even more unreliable.
>
> I expect -O0 performance to depend a lot more on GCC version than -O2.
>
You expect but could you prove it? Please provide two versions of gcc
where you get different simple-* function when compiling with -O0 -S
Versions I checked are
Debian 4.5.3-12
Debian 4.7.1-2
gcc version 4.9.0 20130516 (experimental) (GCC)
Assemblies produced are same for following fragment:
void
*memset (char *s, int c, int n)
{
int i;
for(i=0 ;i<n; i++) s[i] = c;
return s;
}