Re: RFC: #pragma optimization_level

[Mark Mitchell <mark at codesourcery dot com>]

Dale Johannesen wrote:

> So I guess question 1 is, Mark, do you feel negatively enough about this
> feature to block its acceptance in mainline?

I'm not sure that I *could* block it, but, no, I don't feel that negatively.

I think that a #pragma (or attribute) that affects only optimization 
options is less problematic than generic option processing (.e.g, 
flag_writable_strings, as in the email you reference).

I do think that you need to clearly document how inlining plays with 
this.  In particular, if you inline a -O2 function into a -O0 function, 
what happens?  (My suggestion would be that the caller's optimization 
pragmas win.)

Also, you should document what set of optimization options can be 
specified.  I think it should only be ones that do not change the ABI; 
things like -O2, or turning off particular passes are OK, while options 
that change calling conventions, etc., should be disallowed.

Also, you need to say what happens in the situation where the user has 
done "-O2 -fno-gcse" and the #pragma now says "-O2".  Does that reenable 
GCSE?  (I think it should.)

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Mark Mitchell
CodeSourcery, LLC
mark@codesourcery.com
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