Re: optimization/9319: slower code generated for simple loop on linux

[Amnon Cohen <amnon_cohen@yahoo.com>]

The following reply was made to PR optimization/9319; it has been noted by GNATS.

From: Amnon Cohen <amnon_cohen@yahoo.com>
To: ebotcazou@gcc.gnu.org, gcc-bugs@gcc.gnu.org, gcc-prs@gcc.gnu.org,
  nobody@gcc.gnu.org, gcc-gnats@gcc.gnu.org
Cc: amnon@verisity.com
Subject: Re: optimization/9319: slower code generated for simple loop on linux
Date: Thu, 16 Jan 2003 05:30:27 -0800 (PST)

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 Hi ebotcazou,
 Thanks for getting back to me so fast.
 I have done a few more tests, and it seems 
 that this is a regression
 on all platforms  (not just intel) introduced by
 gcc3.1
 Note that the while loop in the example is equivalent
 to
 for (i=0; i<n; i++) s+=i;
 
 The for loop generates faster code.
 
 Another problem, if we compile with
 -funroll-all-loops,
 the loop does not get unrolled on gcc3.2.1, whereas
 it does on gcc3.0
 
 
 Here is the information you asked for.
 For the newer compiler which shows the regression
 
 >gcc321 -v
 Reading specs from
 /usr/local/lib/gcc-lib/i686-pc-linux-gnu/3.2.1/specs
 Configured with: ./configure 
 Thread model: posix
 gcc version 3.2.1
 
 Wheras the old version
 >gcc3 -v
 Reading specs from
 /usr/local/lib/gcc-lib/i686-pc-linux-gnu/3.0.3/specs
 Configured with: ./configure 
 Thread model: single
 gcc version 3.0.3
 
 I have attached the assembler files 
 (produced by gcc -S loop3.c)
 
 The performance is significantly reduced on intel
 linux and on Solaris (I have not sent solaris asm
 files, let me know if you need them). So I do 
 not think that this is architecture related
 
 Please let me know if you need any more info!
 
 - Amnon
 
 --- ebotcazou@gcc.gnu.org wrote:
 > Synopsis: slower code generated for simple loop on
 > linux
 > 
 > Responsible-Changed-From-To: unassigned->ebotcazou
 > Responsible-Changed-By: ebotcazou
 > Responsible-Changed-When: Thu Jan 16 03:58:11 2003
 > Responsible-Changed-Why:
 >     Investigating.
 > State-Changed-From-To: open->feedback
 > State-Changed-By: ebotcazou
 > State-Changed-When: Thu Jan 16 03:58:11 2003
 > State-Changed-Why:
 >     Could you provide us with more details ? What
 > does gcc -v output for each compiler ? Could you
 > post the assembly code generated for the loop by
 > each compiler (gcc -O3 -S) ? On what hardware did
 > you experience the performance hit ?
 > 
 > http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=9319
 
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