[Bug lto/98275] New: -flto=auto fails if nthreads_var is zero, must not pass -j0

[Bug lto/98275] New: -flto=auto fails if nthreads_var is zero, must not pass -j0

[pexu@gcc-bugzilla.mail.kapsi.fi]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98275

            Bug ID: 98275
           Summary: -flto=auto fails if nthreads_var is zero, must not
                    pass -j0
           Product: gcc
           Version: 10.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: lto
          Assignee: unassigned at gcc dot gnu.org
          Reporter: pexu@gcc-bugzilla.mail.kapsi.fi
                CC: marxin at gcc dot gnu.org
  Target Milestone: ---
              Host: mingw64

Hi. 

When using `-flto=auto' if the number of threads is not detected, i.e.
`nthreads_var' equals to zero, lto-wrapper must not pass -j0 to GNU make as -j
expects a positive, non-zero integer (if any given).

>From GNU make manual: ``If the ‘-j’ option is followed by an integer, this is
the number of recipes to execute at once; this is called the number of job
slots. If there is nothing looking like an integer after the ‘-j’ option, there
is no limit on the number of job slots.''.

gcc/lto-wrapper.c:
2001               snprintf (jobs, 31, "-j%ld",
2002                         auto_parallel ? nthreads_var : parallel);

$ make -j0
make: the '-j' option requires a positive integer argument

Tried GNU make 4.2.1 (2016 vintage) and 4.2.93 (2020).  For the latest trunk
argument parsing happens at src/main.c around line 2961 [1];  It basically does
``int i = atoi(arg); if (i < 1 || not-all-chars-are-digits) { handle-bad-arg
}''.


[1] https://git.savannah.gnu.org/cgit/make.git/tree/src/main.c#n2961

[Bug lto/98275] -flto=auto fails if nthreads_var is zero, must not pass -j0

[marxin at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98275

Martin Liška <marxin at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |11.0
             Status|UNCONFIRMED                 |ASSIGNED
   Last reconfirmed|                            |2020-12-14
     Ever confirmed|0                           |1
           Assignee|unassigned at gcc dot gnu.org      |marxin at gcc dot gnu.org

--- Comment #1 from Martin Liška <marxin at gcc dot gnu.org> ---
Thank you for the bug report.

Can you please test the following patch:

diff --git a/gcc/lto-wrapper.c b/gcc/lto-wrapper.c
index 68ccb156521..da1305c1696 100644
--- a/gcc/lto-wrapper.c
+++ b/gcc/lto-wrapper.c
@@ -1780,6 +1780,8 @@ cont1:
        {
          char buf[256];
          init_num_threads ();
+         if (nthreads_var == 0)
+           nthreads_var = 1;
          if (verbose)
            fprintf (stderr, "LTO parallelism level set to %ld\n",
                     nthreads_var);

[Bug lto/98275] -flto=auto fails if nthreads_var is zero, must not pass -j0

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98275

--- Comment #2 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Martin Liska <marxin@gcc.gnu.org>:

https://gcc.gnu.org/g:cab1b0ebc00ea53040afcbe4b91e653a87915092

commit r11-6040-gcab1b0ebc00ea53040afcbe4b91e653a87915092
Author: Martin Liska <mliska@suse.cz>
Date:   Tue Dec 15 09:59:04 2020 +0100

    lto: set nthreads_var to 1 if it is zero

    gcc/ChangeLog:

            PR lto/98275
            * lto-wrapper.c: Do not use -j0 when we are unable to detect
            number of cores.

[Bug lto/98275] -flto=auto fails if nthreads_var is zero, must not pass -j0

[marxin at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98275

Martin Liška <marxin at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|---                         |FIXED

--- Comment #3 from Martin Liška <marxin at gcc dot gnu.org> ---
Should be fixed now.

[Bug lto/98275] -flto=auto fails if nthreads_var is zero, must not pass -j0

[pexu@gcc-bugzilla.mail.kapsi.fi]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98275

--- Comment #4 from Pekka S <pexu@gcc-bugzilla.mail.kapsi.fi> ---
(I wrote this prior the ticked was modifed and the patch committed.)

Thanks.

Applied the patch on the latest trunk, built aarch64-none-gcc cross compiler
(mingw64).  Using -flto=auto -v reports `LTO parallelism level set to 1' and
`make -f <temporary.mk> -j1 all';  Linking now succeeds.

Tested using GNU make 4.2.93 and 4.3 (msys2).

I do not know whether or not the number of processors should be actually
detectable.  I presume I'll be simply using -flto=N (N>1) as it appears to work
just fine.

As a side note behaviour is now slightly different between -flto=auto if
nthreads_var<=1 and -flto=N where N<=1.