On Nov 29, 2007 2:27 AM, Michael Meissner <[EMAIL PROTECTED]> wrote: > One of the things that I've been interested in is adding support to GCC to > compile individual functions with specific target options. I first presented > a > draft at the Google mini-summit, and then another draft at the GCC developer > summit last July. > > In the x86 world this would mean saying that an individual function can use > SSE5 instructions or SSE4.1 instructions. This would simplify things for > people who need to write high performance libraries that run on different > architectures, and need to be optimal on each platform. Ultimately, the goal > is to allow hotspot functions to be compiled several times with different > target specific optimizations. I would welcome any thoughts or suggestions > about this proposal. > > The proposal is at: > http://gcc.gnu.org/wiki/FunctionSpecificOpt
Regarding the static constructors/destructors, we can version them as well. In case a person wishes to annotate them, he can use: __attribute__(sse4a) or change the constructor function name to name__v__sse4a__ or so. He can safely assume that it won't execute if the feature bit isn't present. We would simply ret if the feature bit isn't supported. Multiple attributes are supported for any function, and it shouldnt be a problem :-) This means the detection of features would be done before the program's actual execution. > > Part of the infrastructure work for doing this is already addressed in > function > adaption project and we will work together with that team: > http://gcc.gnu.org/wiki/functionAdaptation > > One of the things that I have considered and not added to the current proposal > is to change most of the -f, -O, -W options for a function. This would be > relatively simple to add once the infrastructure is in place, but it can > really > complicate things, since various optimizations depend on other optimizations > having been done. Similarly, the -mtune= and -march= options can overly > complicate matters. > As for setting -f, there are flags like: stack-protector-all which can not be set at a function level. The problem happens when a flag is set to 0/1 (not 2) and is valid for a whole compilation unit.. (It might be there, I'm saying); We should clearly split the common.opt/annotate it with the required information so we can determine which ones can not be unset when set or vice-versa. The warn/optimization levels would inherit/differenciate from the parent settings (compilation unit or enclosing function). > In addition, attribute(cold) and attribute(hot) will set the optimization > level > to -Os and -O3. > It might be possible that he wishes to optimize for size (not inline function calls/unroll loops, for instance) but he might want it versioned; . Versioning will increase text size only if all versions are loaded during runtime. > I will be away on vacation from December 3-8th, and not reading mail during > that time. > > -- > Michael Meissner, AMD > 90 Central Street, MS 83-29, Boxborough, MA, 01719, USA > [EMAIL PROTECTED] > > > -- Karthik
