On Mon, Sep 3, 2012 at 1:46 PM, Georg-Johann Lay <a...@gjlay.de> wrote: > Gabriel Dos Reis schrieb: > >> On Mon, Sep 3, 2012 at 11:29 AM, Georg-Johann Lay <a...@gjlay.de> wrote: >>> >>> AVR-Libc comes with hand-optimized float support functions written >>> in assembler. These functions use the same naming conventions like >>> libgcc. There are situations where this name clashed lead to performance >>> regression because the functions from libgcc are linked. One example >>> are the new fixed-point support that convert fixed-point to/from float >>> and reference float/int conversion functions from within libgcc. >>> >>> The float implementation in libm.a have been discussed several times >>> with the only result that it is very unlikely that the code will >>> ever be integrated into libgcc because the original authors are no >>> more around. And is is much less work to add a new configure switch >>> than to port and integrate the code, given there were no license issues. >>> One point against such an extension was that such change to the compiler >>> establishes a dependency between the compiler and AVR-Libc, but this >>> decision has been made long ago by accepting code that actually should >>> had been added to libgcc -- but was not for whatever reason. >>> >>> This patch removes that performance regressions by removing the >>> doubly implemented functions from libgcc by means of a new configure >>> option --with-avrlibc. >> >> >> Johann, >> >> as I stated yesterday, I do not understand why there needs to be yet >> another >> configure option. The NATURAL libc for ARV targets is ARV-libc. We >> should not need a switch for that. > > > There is also newlib that is used with avr-gcc. I know this because > some bugs are only triggered for newlib. If there are users that > report bugs if avr-gcc is build for newlib, I'd guess these users are > actually interested in using newlib.
I did not say there was no other libc library. I said that the *natural* libc appears to be AVR-libc. We don't configure GCC/g++ saying --with-libstdc++. -- Gaby > > It's clear that the proposed changes do *not* work with newlib > because newlib does not mimic parts of libgcc. > > Johann > > >>> Moreover, some specs are adjusted so that -lm is treated very much like >>> -lgcc so that the user need not specify -lm by hand for core float >>> support like int/float conversions. >>> >>> Without this patch, LTO compilations also lead to performance regression >>> because lto adds -plugin-opt=-pass-through=-lgcc etc. prior to the -lm >>> specified by the user. >>> >>> Other cases where code is improved are C++ programs, see PR28718 for a >>> discussion. >>> >>> >>> There are less fails in gcc.dg/fixed-point, presumably because the >>> rounding >>> is as expected by the test cases, i.e. there are no rounding errors as >>> mentioned in the review for PR54222: >>> http://gcc.gnu.org/ml/gcc-patches/2012-08/msg01586.html >>> >>> Ok to install? >>> >>> >>> Johann >>> >>> >>> PR target/54461 >>> * configure.ac (noconfigdirs,target=avr-*-*): Add target-newlib, >>> target-libgloss if configured --with-avrlibc. >>> * configure: Regenerate. >>> >>> libgcc/ >>> PR target/54461 >>> * config.host (tmake_file,host=avr-*-*): Add avr/t-avrlibc if >>> configured --with-avrlibc. >>> * config/avr/t-avrlibc: New file. >>> >>> gcc/ >>> PR target/54461 >>> * config.gcc (tm_file,target=avr-*-*): Add avr/avrlibc.h if >>> configured --with-avrlibc. >>> (tm_defines,target=avr-*-*): Add WITH_AVRLIBC if configured >>> --with-avrlibc. >>> * config/avr/avrlibc.h: New file. >>> * config/avr/avr-c.c: Build-in define __WITH_AVRLIBC__ if >>> configured --with-avrlibc. >> >> >
