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Re: Ask for help

From: John Fine <johnsfine at verizon dot net>
To: gcc-help at gcc dot gnu dot org
Cc: wanxia dot wei at unb dot ca, Andrew Haley <aph at redhat dot com>
Date: Tue, 17 Mar 2009 11:02:38 -0400
Subject: Re: Ask for help
References: <1237301131.49bfb78bd12ec@webmail.unb.ca>

If your meaning for the word "performance" is the usual meaning, the earlier response by Andrew Haley answers the whole question.

But the way you phrased the question makes me think you meant "behavior" when you wrote "performance".

-fno-strict-aliasing can give you correct behavior from a program that incorrectly uses a reinterpret_cast or similar operation. That should be considered a bug, and if there are few of those in your code, you should find and correct them.

Some old code has enough incorrect reinterpret_cast operations that correcting them is impractical and you need the -fno-strict-aliasing

I'm not sure what -DNDEBUG or -static might change in the behavior or performance of your code. I'm just guessing that -fno-strict-aliasing is the important difference.

Wei, Wanxia wrote:

gcc -m32 -O3 -DNDEBUG -fno-strict-aliasing -static –lm

gcc -m32 –O3 –lm

...

 the
different performance of the two executables of my C program means there are bugs in
this program?

Follow-Ups:
- Re: Ask for help
  - From: Wei, Wanxia

References:
- Ask for help
  - From: Wei, Wanxia

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