Re: Some strict aliasing related fun

6 msg	FW: Errors issued while building GCC
1 msg	Re: Compiler fails to find header files.

Some strict aliasing related fun
\ Raymond Sheh (28 Nov 2007)
. \ corey taylor (28 Nov 2007)
. . \ Raymond Sheh (28 Nov 2007)
. . . \ corey taylor (28 Nov 2007)
. . . . \ Raymond Sheh (28 Nov 2007)
. \ Brian Dessent (28 Nov 2007)
. . \ Raymond Sheh (28 Nov 2007)
. \ Brian Dessent (28 Nov 2007)

3 msg	Compiler isn't finding system header files
2 msg	WG: [gnu.org #342187] licensing and copyright
69 msg	reduce compilation times?
1 msg	Re: gcc 4.2.2, libgomp under cygwin
9 msg	Installation Problem
2 msg	Inheritance problem
4 msg	public method hidden by protected one
3 msg	Issue with apache compilation : memmove & b...
2 msg	compiling fortran support in 4.2.2 on solaris
1 msg	build fails using gcc-4.2.1 (5531) on OSX 10.4....
2 msg	collect2: ld terminated with signal 11 [Segment...
1 msg	gcc - multilib - and specs files.
6 msg	Measuring short times
5 msg	GCC Problem, 32-bit vs. 64-bit?
5 msg	How do I use GNAT to develop an OS kernel?
2 msg	Targetting strange CPU architecture
5 msg	error installing previous gcc version

Subject:	Re: Some strict aliasing related fun
Group:	Gcc-help
From:	Brian Dessent
Date:	28 Nov 2007

Raymond Sheh wrote:

> > Specifying -fsome-optimization without an n >= 0 level of -On is a
> > no-op. In other words, optimization must be enabled in order to do any
> > optimization.

I meant > 0 here, as -O0 means no optimization.

> This is all being tested on pretty much a standard Kubuntu 7.10 (Gutsy
> Gibbon) install using the distro's GCC packages ... perhaps is there
> some way of seeing what the defaults are set to? Is it possible that for
> some reason some optimisation level (below -O1, if there is such a
> thing) is enabled by default?

If you don't specify any -O the default is -O0, which is no
optimizations.

I don't know why you are able to also trigger a failure without
optimizations just by giving -fstrict-aliasing -fschedule-insns, but
it's kind of beside the point since combining source that violates the
aliasing rules with -fstrict-aliasing is just setting yourself up for
failure, regardless of the details.

Brian