Re: Bug#456034: fenix: compile with -O1
On 14/12/2007, Simon Ruggier <simon80@gmail.com> wrote:
> On 12/14/07, Jon Dowland <lists@alcopop.org> wrote:
> > My understanding is that -O2 should never result in incorrect/failing
> > code and -O3 can, but I'm not sure where I get that notion frmo.
>
> I would have thought one would get it from the gcc man page, but when
> I looked, I couldn't find anything explicit.
It can be found through 'info': info gcc
Section: 3.10 Options That Control Optimization
"`-O2'
Optimize even more. GCC performs nearly all supported
optimizations that do not involve a space-speed tradeoff. The
compiler does not perform loop unrolling or function inlining when
you specify `-O2'. As compared to `-O', this option increases
both compilation time and the performance of the generated code.
`-O2' turns on all optimization flags specified by `-O'. It also
turns on the following optimization flags:
-fthread-jumps
-fcrossjumping
-foptimize-sibling-calls
-fcse-follow-jumps -fcse-skip-blocks
-fgcse -fgcse-lm
-fexpensive-optimizations
-fstrength-reduce
-frerun-cse-after-loop -frerun-loop-opt
-fcaller-saves
-fpeephole2
-fschedule-insns -fschedule-insns2
-fsched-interblock -fsched-spec
-fregmove
-fstrict-aliasing
-fdelete-null-pointer-checks
-freorder-blocks -freorder-functions
-falign-functions -falign-jumps
-falign-loops -falign-labels
-ftree-vrp
-ftree-pre
Please note the warning under `-fgcse' about invoking `-O2' on
programs that use computed gotos.
"
Not sure if that helps.
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