Optimization Switches

[Andrew Haley]

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On 08/26/2010 12:56 PM, sharjeel@cse.iitb.ac.in wrote:
> Hi,
> I wish to selectively enable specific optimizations to observe its effect
> on the source. My project requires me to do this analysis. It seemed, the
> -f* flags would enable me to do that. But it turns out that individual
> optimizations can't be enabled like that, and all the optimizations at a
> specific level gets enabled when I use a  -Ox switch. This faq  at
> http://gcc.gnu.org/wiki/FAQ#optimization-options, says this too.
> 
> So here are my two questions :
> 
> a) Is there any way to observe the effect of a particular optimization,
> without the obvious option of using a lot of -fno switches.

Use the -fdump-tree-all and the RTL dumps.

> b) And do the -f* switches serve any purpose, if I can't enable individual
> optimizations using them.

You can turn some individual optimizations on and off, but only if optimization
is enabled.

Andrew.