https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84402
--- Comment #49 from Martin Liška <marxin at gcc dot gnu.org> ---
One more observation I made, apparently we're trying to sort (in Makefile.in)
OBJS with the biggest at the very beginning:
1295 # Language-independent object files.
1296 # We put the *-match.o and insn-*.o files first so that a parallel make
1297 # will build them sooner, because they are large and otherwise tend to
be
1298 # the last objects to finish building.
1299 OBJS = \
1300 gimple-match.o \
1301 generic-match.o \
1302 insn-attrtab.o \
1303 insn-automata.o \
That's fine, plus we introduce dependency for all objects to depend on
generated_files:
4441 # In order for parallel make to really start compiling the expensive
4442 # objects from $(OBJS) as early as possible, build all their
4443 # prerequisites strictly before all objects.
4444 $(ALL_HOST_OBJS) : | $(generated_files)
Using that, we should see gimple-match.o being spawned very soon, but it's not
the case. Imagine you have already built all-host and let's see what happens:
$ rm -f gimple-match.o ; rm -f tree*.o && make -j4 --debug=b libbackend.a 2>&1
| less
...
File 'gimple-match.o' does not exist.
Prerequisite 'cs-bconfig.h' is newer than target 'bconfig.h'.
Must remake target 'bconfig.h'.
Prerequisite 'cstamp-h' is newer than target 'auto-host.h'.
Must remake target 'auto-host.h'.
Prerequisite 's-options' is newer than target
'optionlist'.
Must remake target 'optionlist'.
Prerequisite 's-gtyp-input' is newer than target
'gtyp-input.list'.
Must remake target 'gtyp-input.list'.
Prerequisite 's-bversion' is newer than target
'bversion.h'.
Must remake target 'bversion.h'.
Prerequisite 'cs-config.h' is newer than target 'config.h'.
Must remake target 'config.h'.
...
File 'tree-vrp.o' does not exist.
File 'tree.o' does not exist.
Prerequisite 's-i386-bt' is newer than target 'i386-builtin-types.inc'.
Must remake target 'i386-builtin-types.inc'.
File 'gimple-match.o' does not exist.
Prerequisite 's-modes-h' is newer than target 'insn-modes.h'.
Must remake target 'insn-modes.h'.
Prerequisite 's-modes-inline-h' is newer than target
'insn-modes-inline.h'.
Must remake target 'insn-modes-inline.h'.
Prerequisite 's-version' is newer than target 'version.h'.
Must remake target 'version.h'.
Prerequisite 's-options-h' is newer than target 'options.h'.
Must remake target 'options.h'.
Prerequisite 's-genrtl-h' is newer than target 'genrtl.h'.
Must remake target 'genrtl.h'.
Prerequisite 's-modes-m' is newer than target 'min-insn-modes.cc'.
Must remake target 'min-insn-modes.cc'.
...
File 'gimple-match.o' does not exist.
Prerequisite 's-gtype' is newer than target 'gtype-desc.h'.
Must remake target 'gtype-desc.h'.
Prerequisite 's-constants' is newer than target
'insn-constants.h'.
Must remake target 'insn-constants.h'.
...
Must remake target 'tree-affine.o'.
g++ -fno-PIE -c -g -DIN_GCC -fno-exceptions -fno-rtti
-fasynchronous-unwind-tables -W -Wall -Wno-narrowing -Wwrite-strings
-Wcast-qual -Wmissing-format-attribute -Woverloaded-virtual -pedantic
-Wno-long-long -Wno-variadic-macros -Wno-overlength-strings -fno-common
-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 tree-affine.o -MT
tree-affine.o -MMD -MP -MF ./.deps/tree-affine.TPo
/home/marxin/Programming/gcc/gcc/tree-affine.cc
File 'tree-call-cdce.o' does not exist.
Must remake target 'tree-call-cdce.o'.
g++ -fno-PIE -c -g -DIN_GCC -fno-exceptions -fno-rtti
-fasynchronous-unwind-tables -W -Wall -Wno-narrowing -Wwrite-strings
-Wcast-qual -Wmissing-format-attribute -Woverloaded-virtual -pedantic
-Wno-long-long -Wno-variadic-macros -Wno-overlength-strings -fno-common
-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 tree-call-cdce.o -MT
tree-call-cdce.o -MMD -MP -MF ./.deps/tree-call-cdce.TPo
/home/marxin/Programming/gcc/gcc/tree-call-cdce.cc
File 'tree-cfg.o' does not exist.
Must remake target 'tree-cfg.o'.
g++ -fno-PIE -c -g -DIN_GCC -fno-exceptions -fno-rtti
-fasynchronous-unwind-tables -W -Wall -Wno-narrowing -Wwrite-strings
-Wcast-qual -Wmissing-format-attribute -Woverloaded-virtual -pedantic
-Wno-long-long -Wno-variadic-macros -Wno-overlength-strings -fno-common
-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 tree-cfg.o -MT
tree-cfg.o -MMD -MP -MF ./.deps/tree-cfg.TPo
/home/marxin/Programming/gcc/gcc/tree-cfg.cc
File 'tree-cfgcleanup.o' does not exist.
Must remake target 'tree-cfgcleanup.o'.
So gimple-match.o has a complex dependencies that are somehow under
investigation and that's why it doesn't start early :/
It's likely related to various ' $(STAMP) $name' we use, if I consider
one:
gtyp-input.list: s-gtyp-input ; @true
s-gtyp-input: Makefile
@: $(call write_entries_to_file,$(GTFILES),tmp-gi.list)
$(SHELL) $(srcdir)/../move-if-change tmp-gi.list gtyp-input.list
$(STAMP) s-gtyp-input
Here we touch 's-gtyp-input' later than gtyp-input.list is created and thus
gtyp-input.list always need
to be remade becase it's dependency s-gtyp-input is newer. Similarly for many
other rules:
gimple-match.cc: s-match gimple-match-head.cc ; @true
s-match: build/genmatch$(build_exeext) $(srcdir)/match.pd cfn-operators.pd
$(RUN_GEN) build/genmatch$(build_exeext) --gimple $(srcdir)/match.pd \
> tmp-gimple-match.cc
$(RUN_GEN) build/genmatch$(build_exeext) --generic $(srcdir)/match.pd \
> tmp-generic-match.cc
$(SHELL) $(srcdir)/../move-if-change tmp-gimple-match.cc \
gimple-match.cc
$(SHELL) $(srcdir)/../move-if-change tmp-generic-match.cc \
generic-match.cc
$(STAMP) s-match
Here it's even more complicated, I think s-match should be only updated if
generic-match.cc is touched,
otherwise, we again end up younger s-match than gimple-match.cc.
Can please any GNU make expect judge here? Starting e.g. gimple-match.cc early
would really help
to speed up the build process.
