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people:holger [2007/08/20 06:27]
holger
people:holger [2007/08/20 11:37] (current)
holger
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     Status: unfortunately no difference at all. local branch exists, may be included in the attr changes for completeness.     Status: unfortunately no difference at all. local branch exists, may be included in the attr changes for completeness.
   * somewhere in between: install git, learn to use it, research documentation on attributes (useful link: http://​www.ohse.de/​uwe/​articles/​gcc-attributes.html)   * somewhere in between: install git, learn to use it, research documentation on attributes (useful link: http://​www.ohse.de/​uwe/​articles/​gcc-attributes.html)
 +
  
  
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   * Break up string.c in used and unused functions. also set pure attributes. status: done, not yet merged.   * Break up string.c in used and unused functions. also set pure attributes. status: done, not yet merged.
  
 +  * optimizing memset. status: should be optimal in size now (also all the other functions in string.h) checked in as "​memset"​ branch. this is an overall win in codesize (most notably for undinet, multiboot ​ and monojob). warnings mentioned here earlier have been successfully silenced, also the code saw a lot more optimizations (memmove optimization,​ memcpy break-even checked and adjusted, cx load trick for all possible functions and values).
 +  * included attributes on hci subdir (branch for that is slightly incorrectly named "​curses"​). also split up curses a bit further, but only marginally (most of it isn't used anyway) - branch that includes this in addition to the former is "​cursessplit"​
 +  * biggest win with attributes was not to inline certain functions (as earlier results on -fno-inline and -finline-limit suggested). investigated all the functions that turned out to decrease in size with a more aggressive inline-limit and found several cases where the effect could be pinpointed to a function or two. set these to noinline (because otherwise, gcc's default inline limit with -Os seems mostly fine - i think it just doesn'​t take the lower call overhead with regparm properly into account). most interesting result was that for minimal codesize with the new regparm calling conventions,​ we actually don't want to have the list functions static inline anymore (even the really simple __list_del is only marginally a win inlined, the others aren'​t). branch named "​inline"​ committed (which is based on the memset branch because before that memset/​memmove would also have been candidates for noinline)
 +  * other than noinline in certain cases, attributes unfortunately turned out to be mostly insignificant for code size. nonnull helps only in special cases (by optimizing away any explicit pointer checks that might be inside), but as it gives us additional compile time checks, it's probably still a good idea (included them in the parts that were committed for other reasons, see above). pure mostly makes no difference either (haven'​t seen effects of more than +/- 2-3 bytes, seems to even out, and we don't have a lot of them - same). don't think i spotted a const function yet.
  
  
  
 +  * commited the malloc annotations (to strings branch, as that wasn't merged yet anyway)
  
  
-==== Currently in progress ==== 
  
-  * optimizing memset. status: first take at memset optimization (that actually looks good for all the tests i could think of ;) checked in as memset branch. had a "save 1 byte" idea that could also be applied to memcpy. will check and correct new break-even for extern memcpy while i'm at it. this is an overall win in codesize (most notably for undinet, multiboot ​ and monojob). warnings mentioned here earlier have been successfully silenced, also the code saw some more optimizations (memmove, cx load trick for all possible functions and values). i think it should be optimal in size now. 
-  * more malloc annotations (will merge and push after strings is merged) - status: have something i can commit and check in as soon as strings is merged. 
-  * included attributes on hci subdir. curses split up a bit further, but only marginally (most of it isn't used anyway) 
  
- +==== Things to do now that we have "​pencils down" for code ====
-==== Things to be done next ==== +
- +
-  * start annotating functions with attributes, starting with the common ones (may be a large amount of work that might not lead to anything useful, but at least we know that then - and it might inspire ideas on other modifications to commonly used functions) +
- +
-==== Other things still to do ====+
  
   * write up some docs for the conversions that helped, give some background, maybe illustrated by examples of the generated code before and after.   * write up some docs for the conversions that helped, give some background, maybe illustrated by examples of the generated code before and after.
   * write up docs on when functions (or other symbols) should be attributed by what.   * write up docs on when functions (or other symbols) should be attributed by what.
-  * whatever else comes up 
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