Re: New option to do fine grain control [on|off] of micro-arch specific features : -mtune-ctrl=....

["Joseph S. Myers" <joseph at codesourcery dot com>]

On Sun, 4 Aug 2013, Andi Kleen wrote:

> Richard Biener <richard.guenther@gmail.com> writes:
> >
> > The patch fails to add documentation.
> 
> That seems like a feature, it's likely not useful for the general
> public. More for specialized tools that automatically search
> for the best tuning.

If such a tool is not part of GCC itself, then it is a user of GCC and 
documentation should be provided for those writing such a tool.

Options should be undocumented in very limited cases such as multiple 
variant spellings where only one should be used but others are accepted 
because they were historically, or whether the user interface to an option 
is separate from the internal option passed to cc1 (the documentation is 
of options as passed to the driver, but the .opt file may describe options 
passed to cc1 as a result of other options being passed to the driver), or 
the option really is only for use within the build of GCC itself.  
Otherwise, the strong presumption is that all options should be 
documented, with appropriate caveats as applicable about the cases where 
an option is useful.

> > And I am nervous about testing
> > coverage - is this considered a development option only or are random
> > combinations expected to work in all situations? I expect not, thus
> > this looks like a dangerous option?
> 
> When it's undocumented it doesn't need to work in every situation?

No input files and command-line arguments whatsoever to the driver should 
result in ICEs, including undocumented options.

-- 
Joseph S. Myers
joseph@codesourcery.com