[Bug ld/26766] Support standalone PGO build

[mliska at suse dot cz]

https://sourceware.org/bugzilla/show_bug.cgi?id=26766

--- Comment #12 from Martin Liska <mliska at suse dot cz> ---
> I pass -flto=jobserver to the PGO build.  The separate --enable-lto-build
> isn't very useful.  You can build binutils with LTO by passing -flto to
> CFLAGS. I will rename --enable-pgo-bootstrap=lto to --enable-pgo-build=lto
> since the newly built binutils is used only for PGO training.

All right, as mentioned, it works for me.

About the jobserver support, when using GCC 11, one can see the following
warning when a sub-make is not run with '+' rule:

libtool: link: gcc -W -Wall -Wstrict-prototypes -Wmissing-prototypes -Wshadow
-Wstack-usage=262144 -Wwrite-strings -I../../gas/../zlib -g -O2
-fprofile-generate -flto=jobserver -o as-new app.o as.o atof-generic.o
compress-debug.o cond.o depend.o dwarf2dbg.o dw2gencfi.o ecoff.o ehopt.o expr.o
flonum-copy.o flonum-konst.o flonum-mult.o frags.o hash.o input-file.o
input-scrub.o listing.o literal.o macro.o messages.o output-file.o read.o
remap.o sb.o stabs.o subsegs.o symbols.o write.o config/tc-i386.o
config/obj-elf.o config/atof-ieee.o  ../opcodes/.libs/libopcodes.a
../bfd/.libs/libbfd.a -L/tmp/binutils-gdb/objdir/zlib -lz
../libiberty/libiberty.a -ldl
lto-wrapper: warning: jobserver is not available: '--jobserver-auth=' is not
present in 'MAKEFLAGS'

I can fix it with the following change:

diff -u gas/Makefile.orig gas/Makefile
--- gas/Makefile.orig   2020-10-26 18:41:45.992955514 +0100
+++ gas/Makefile        2020-10-26 18:42:21.976647698 +0100
@@ -1081,8 +1081,8 @@
        config/$(DEPDIR)/$(am__dirstamp)

 as-new$(EXEEXT): $(as_new_OBJECTS) $(as_new_DEPENDENCIES)
$(EXTRA_as_new_DEPENDENCIES) 
-       @rm -f as-new$(EXEEXT)
-       $(AM_V_CCLD)$(LINK) $(as_new_OBJECTS) $(as_new_LDADD) $(LIBS)
+       + @rm -f as-new$(EXEEXT)
+       + $(AM_V_CCLD)$(LINK) $(as_new_OBJECTS) $(as_new_LDADD) $(LIBS)

 itbl-test$(EXEEXT): $(itbl_test_OBJECTS) $(itbl_test_DEPENDENCIES)
$(EXTRA_itbl_test_DEPENDENCIES) 
        @rm -f itbl-test$(EXEEXT)

but I don't know how to modify the original gas/Makefile.am
?

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