On Mon, May 20, 2013 at 4:28 PM, Winfried Magerl <winfried.mag...@t-online.de> wrote: > Hi, > > On Mon, May 20, 2013 at 09:40:52AM -0300, Adhemerval Zanella wrote: >> Hi, >> >> Thanks for reporting it, I saw it too when building glibc with gcc-trunk. >> Carlos O'Donell already reported it could be an issue to glibc at >> http://sourceware.org/ml/libc-alpha/2013-02/msg00299.html and I also noted >> it causes PTL issues too at >> http://sourceware.org/ml/libc-alpha/2013-04/msg00124.html >> I have proposed a patch >> http://sourceware.org/ml/libc-alpha/2013-04/msg00196.html >> so configure can check if compiler transform loops into libc functions >> calls, but >> Andreas Jaeger and Roland McGrath didn't approve the approach. >> >> Although, the problem persist and I think we need to figure out how to >> proceed >> before 2.18 release. Based on the loader memset recursion call you observe I >> do >> suggest to use my approach and add '-fno-tree-loop-distribute-patterns' on >> rtld-memset.os object. >> >> Any comments? > > tree-loop-distribute-patterns is enabled on gcc-4.7.3 with -O3: > > # /usr/gcc47/bin/gcc --version > gcc (GCC) 4.7.3 > [....] > # /usr/gcc47/bin/gcc -c -Q -O3 --help=optimizers | fgrep > tree-loop-distribute-patterns > -ftree-loop-distribute-patterns [enabled] > > And it looks like it's the default for a long time: > > # fgrep OPT_ftree_loop_distribute_patterns gcc-*/gcc/opts.c > gcc-4.6.3/gcc/opts.c: { OPT_LEVELS_3_PLUS, > OPT_ftree_loop_distribute_patterns, NULL, 1 }, > gcc-4.7.0/gcc/opts.c: { OPT_LEVELS_3_PLUS, > OPT_ftree_loop_distribute_patterns, NULL, 1 }, > gcc-4.7.1/gcc/opts.c: { OPT_LEVELS_3_PLUS, > OPT_ftree_loop_distribute_patterns, NULL, 1 }, > gcc-4.7.2/gcc/opts.c: { OPT_LEVELS_3_PLUS, > OPT_ftree_loop_distribute_patterns, NULL, 1 }, > gcc-4.7.3/gcc/opts.c: { OPT_LEVELS_3_PLUS, > OPT_ftree_loop_distribute_patterns, NULL, 1 }, > gcc-4.8.0/gcc/opts.c: { OPT_LEVELS_3_PLUS, > OPT_ftree_loop_distribute_patterns, NULL, 1 }, > > I wonder what's the difference between gcc-4.7.3 and gcc-4.8.x for > 'tree-loop-distribute-patterns' ........
It's better in recognizing patterns that look like memset/memcpy. Don't use it if you build TUs which contain memset/memcpy implementations. Richard. > regards > > winfried >
