On Fri, May 21, 2021 at 5:25 AM Martin Liška <mli...@suse.cz> wrote: > > On 5/20/21 2:54 PM, Richard Biener wrote: > > On Thu, May 20, 2021 at 2:34 PM Martin Liška <mli...@suse.cz> wrote: > >> > >> Hello. > >> > >> I've got a patch candidate that leverages partial linking for a couple of > >> selected object files. > >> > >> I'm sending make all-host- jX results for my machine: > >> > >> before: 3m18s (user 32m52s) > >> https://gist.githubusercontent.com/marxin/223890df4d8d8e490b6b2918b77dacad/raw/1dd5eae5001295ba0230a689f7edc67284c9b742/gcc-all-host.svg > >> > >> after: 2m57m (user 35m) > >> https://gist.githubusercontent.com/marxin/223890df4d8d8e490b6b2918b77dacad/raw/d659b2187cf622167841efbbe6bc93cb33855fa9/gcc-all-host-partial-lto.svg > >> > >> One can utilize it with: > >> make -j16 all-host PARTIAL_LTO=1 > >> > >> @Segher, Andrew: Can you please measure time improvement for your slow > >> bootstrap? > >> One can also tweak --param=lto-partitions=16 param value. > >> > >> Thoughts? > > > > You're LTO linking multiple objects here - that's almost as if you > > were doing this > > for the whole of libbackend.a ... so $(OBJS)_CLFAGS += -flto and in the > > libbackend.a rule do a similar partial link trick. > > Yeah, apart from that one can't likely do partial linking for an archive: > > $ g++ -no-pie -flto=auto --param=lto-partitions=16 -flinker-output=nolto-rel > -r libbackend.a > collect2: fatal error: ld terminated with signal 11 [Segmentation fault], > core dumped > compilation terminated. > > while ld.bfd immediately finishes. > > > > > That gets you half of a LTO bootstrap then. > > > > So why did you go from applying this per-file to multiple files? Does > > $(LINKER) > > have a proper rule to pick up a jobserver? > > > > When upstreaming in any form you probably have to gate it on bootstrap-lto > > being not active. > > Sure, that's reasonable, we can likely detect a -flto option in $(COMPILE), > right? > > One more thing I face is broken dependency: > $ make clean && make -j32 PARTIAL_LTO=1 > > g++ -fcf-protection -fno-PIE -c -g -DIN_GCC -fPIC -fno-exceptions > -fno-rtti -fasynchronous-unwind-tables -W -Wall -Wno-narrowing > -Wwrite-strings -Wcast-qual -Wno-error=format-diag -Wmissing-format-attribute > -Woverloaded-virtual -pedantic -Wno-long-long -Wno-variadic-macros > -Wno-overlength-strings -fno-common -Wno-unused -DHAVE_CONFIG_H -I. -I. > -I/home/marxin/Programming/gcc/gcc -I/home/marxin/Programming/gcc/gcc/. > -I/home/marxin/Programming/gcc/gcc/../include > -I/home/marxin/Programming/gcc/gcc/../libcpp/include > -I/home/marxin/Programming/gcc/gcc/../libcody > -I/home/marxin/Programming/gcc/gcc/../libdecnumber > -I/home/marxin/Programming/gcc/gcc/../libdecnumber/bid -I../libdecnumber > -I/home/marxin/Programming/gcc/gcc/../libbacktrace -o gimple-match-lto.o > -MT gimple-match-lto.o -MMD -MP -MF ./.deps/gimple-match-lto.TPo > gimple-match.c -flto > g++ -fcf-protection -fno-PIE -c -g -DIN_GCC -fPIC -fno-exceptions > -fno-rtti -fasynchronous-unwind-tables -W -Wall -Wno-narrowing > -Wwrite-strings -Wcast-qual -Wno-error=format-diag -Wmissing-format-attribute > -Woverloaded-virtual -pedantic -Wno-long-long -Wno-variadic-macros > -Wno-overlength-strings -fno-common -Wno-unused -DHAVE_CONFIG_H -I. -I. > -I/home/marxin/Programming/gcc/gcc -I/home/marxin/Programming/gcc/gcc/. > -I/home/marxin/Programming/gcc/gcc/../include > -I/home/marxin/Programming/gcc/gcc/../libcpp/include > -I/home/marxin/Programming/gcc/gcc/../libcody > -I/home/marxin/Programming/gcc/gcc/../libdecnumber > -I/home/marxin/Programming/gcc/gcc/../libdecnumber/bid -I../libdecnumber > -I/home/marxin/Programming/gcc/gcc/../libbacktrace -o generic-match-lto.o > -MT generic-match-lto.o -MMD -MP -MF ./.deps/generic-match-lto.TPo > generic-match.c -flto > > In file included from ./tm.h:26, > from /home/marxin/Programming/gcc/gcc/backend.h:28, > from > /home/marxin/Programming/gcc/gcc/generic-match-head.c:23, > from generic-match.c:4: > /home/marxin/Programming/gcc/gcc/config/i386/i386.h:2286:10: fatal error: > insn-attr-common.h: No such file or directory > 2286 | #include "insn-attr-common.h" > | ^~~~~~~~~~~~~~~~~~~~ > compilation terminated. > make: *** [Makefile:2678: generic-match-lto.o] Error 1 > make: *** Waiting for unfinished jobs.... > > In file included from ./tm.h:26, > from /home/marxin/Programming/gcc/gcc/backend.h:28, > from > /home/marxin/Programming/gcc/gcc/gimple-match-head.c:23, > from gimple-match.c:4: > /home/marxin/Programming/gcc/gcc/config/i386/i386.h:2286:10: fatal error: > insn-attr-common.h: No such file or directory > 2286 | #include "insn-attr-common.h" > | ^~~~~~~~~~~~~~~~~~~~ > > I explicitly added: > gimple-match.o: gimple-match.c $(generated_files) > generic-match.o: generic-match.c $(generated_files) > > But it's not obeyed.
Please remember that not all targets support LTO so a fallback to a non-partial-LTO build needs to be provided and automatically invoked for those targets. Thanks, David
