Compiler Optimization - Revision history

Tim Bird at 15:44, 18 December 2012

2012-12-18T15:44:33Z

Tim Bird: add to categories

2011-02-05T00:54:35Z

add to categories

Peter Huewe: Added Safe CFlags link, changed Tim Riker Link

2010-05-18T00:52:16Z

Added Safe CFlags link, changed Tim Riker Link

Berkus: fix formatting

2009-04-07T01:26:32Z

fix formatting

Berkus: add verbatim excerpt about dangers of -O3

2009-04-07T01:25:37Z

add verbatim excerpt about dangers of -O3

Berkus: add link to -Ox optimizations article

2009-04-07T01:21:01Z

add link to -Ox optimizations article

RBot: Bot (Edward's framework)

2007-03-06T03:32:10Z

Bot (Edward's framework)

New page

Here's a good overview on compiler optimizations:
http://en.wikipedia.org/wiki/Compiler_optimization

Here's some info about GCC optimization techniques:
http://www.redhat.com/software/gnupro/technical/gnupro_gcc.html

If you know of a good reference for what the effect of
-Os are with gcc, please put it here:

In the following [http://gcc.gnu.org/ml/gcc/2004-04/msg01409.html e-mail],
Jim Wilson, who apparently supports gcc, writes:

<pre>
From: Jim Wilson <wilson at specifixinc dot com>
Date: Thu, 29 Apr 2004 15:58:28 -0700
Subject: Re: optimization issue about -O2 and -Os
------------------------------------------------------------
...
The -Os option is buggy. You might want to report a bug into our bugzilla
bug datase. See http://gcc.gnu.org/bugs.html for more info on reporting bugs.

Though the -Os option is based on the -O2 option, it is a different option, that
generates different code, and has different bugs.
</pre>

[[Tim Riker]]: this is a bit overly dramtic. -Os is widely used and widely supported. The link is to a thread about general information and does not refer to any specific bug from what I can see. Try -Os out. If you have issues, try -O2 instead. In general -Os will work. Be very careful in tweaking kernel optimizations. There is kernel code that only works with the existing optimizations.

@@ Line 32: / Line 32: @@
 Gentoo has also a very good overview over [http://en.gentoo-wiki.com/wiki/Safe_Cflags Safe Cflags] for different architectures and cpus.
 [[Category:System Size]]
 [[Category:Compiler]]

← Older revision		Revision as of 00:54, 5 February 2011
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	Gentoo has also a very good overview over [http://en.gentoo-wiki.com/wiki/Safe_Cflags Safe Cflags] for different architectures and cpus.		Gentoo has also a very good overview over [http://en.gentoo-wiki.com/wiki/Safe_Cflags Safe Cflags] for different architectures and cpus.
		+
		+	[[Category:System Size]]
		+	[[Category:Compiler]]

← Older revision		Revision as of 00:52, 18 May 2010
Line 28:		Line 28:
	</pre>		</pre>

−	[[Tim Riker]]: this is a bit overly dramtic. -Os is widely used and widely supported. The link is to a thread about general information and does not refer to any specific bug from what I can see. Try -Os out. If you have issues, try -O2 instead. In general -Os will work. Be very careful in tweaking kernel optimizations. There is kernel code that only works with the existing optimizations.	+	[[User:TimRiker\|Tim Riker]]: this is a bit overly dramtic. -Os is widely used and widely supported. The link is to a thread about general information and does not refer to any specific bug from what I can see. Try -Os out. If you have issues, try -O2 instead. In general -Os will work. Be very careful in tweaking kernel optimizations. There is kernel code that only works with the existing optimizations.
		+
		+
		+	Gentoo has also a very good overview over [http://en.gentoo-wiki.com/wiki/Safe_Cflags Safe Cflags] for different architectures and cpus.

@@ Line 8: / Line 8: @@
 A note of warning from [http://www.gentoo.org/doc/en/gcc-optimization.xml Gentoo wiki] on optimization flags:
-<pre>
 -O3: This is the highest level of optimization possible, and also the riskiest. It will take a longer time to compile your code with this option, and in fact it should not be used system-wide with gcc 4.x. The behavior of gcc has changed significantly since version 3.x. In 3.x, -O3 has been shown to lead to marginally faster execution times over -O2, but this is no longer the case with gcc 4.x. Compiling all your packages with -O3 will result in larger binaries that require more memory, and will significantly increase the odds of compilation failure or unexpected program behavior (including errors). The downsides outweigh the benefits; remember the principle of diminishing returns. Using -O3 is not recommended for gcc 4.x.
-</pre>
 In the following [http://gcc.gnu.org/ml/gcc/2004-04/msg01409.html e-mail],

← Older revision		Revision as of 01:25, 7 April 2009
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	Effects of optimization options are explained in [http://www.linuxjournal.com/article/7269 this LJ article].		Effects of optimization options are explained in [http://www.linuxjournal.com/article/7269 this LJ article].
		+
		+	A note of warning from [http://www.gentoo.org/doc/en/gcc-optimization.xml Gentoo wiki] on optimization flags:
		+	<pre>
		+	-O3: This is the highest level of optimization possible, and also the riskiest. It will take a longer time to compile your code with this option, and in fact it should not be used system-wide with gcc 4.x. The behavior of gcc has changed significantly since version 3.x. In 3.x, -O3 has been shown to lead to marginally faster execution times over -O2, but this is no longer the case with gcc 4.x. Compiling all your packages with -O3 will result in larger binaries that require more memory, and will significantly increase the odds of compilation failure or unexpected program behavior (including errors). The downsides outweigh the benefits; remember the principle of diminishing returns. Using -O3 is not recommended for gcc 4.x.
		+	</pre>

	In the following [http://gcc.gnu.org/ml/gcc/2004-04/msg01409.html e-mail],		In the following [http://gcc.gnu.org/ml/gcc/2004-04/msg01409.html e-mail],

@@ Line 5: / Line 5: @@
 http://www.redhat.com/software/gnupro/technical/gnupro_gcc.html
-If you know of a good reference for what the effect of
+Effects of optimization options are explained in [http://www.linuxjournal.com/article/7269 this LJ article].
--Os are with gcc, please put it here:
 In the following [http://gcc.gnu.org/ml/gcc/2004-04/msg01409.html e-mail],