Re: testsuite requires LTO?

[Richard Biener <richard.guenther@gmail.com>]

On Tue, Apr 12, 2022 at 9:07 AM Richard Biener
<richard.guenther@gmail.com> wrote:
>
> On Tue, Apr 12, 2022 at 1:53 AM Steve Kargl via Gcc <gcc@gcc.gnu.org> wrote:
> >
> > If I configure gcc with the following
> >
> > ../gccx/configure --prefix=$HOME/work/x --enable-languages=c,c++,fortran \
> >   --enable-bootstrap --disable-nls --enable-checking --disable-multilib \
> >   --disable-libsanitizer --disable-lto.
> >
> > then bootstrap gcc, why do I see 1000s of failures with
> >
> > % cd gcc
> > % gmake -j7 check-c
> > ...
> > FAIL: gcc.dg/torture/pr64365.c   -O2 -flto  (test for excess errors)
> > FAIL: gcc.dg/torture/pr61786.c   -O2 -flto  (test for excess errors)
> > FAIL: gcc.dg/torture/pr63380-2.c   -O2 -flto  (test for excess errors)
> > FAIL: gcc.dg/torture/pr65270-2.c   -O2 -flto  (test for excess errors)
> >
> > Should the testsuite recognize that gcc is built without LTO support?
>
> Yes, it does, in testsuite/lib/gcc-dg.exp
>
> if [info exists TORTURE_OPTIONS] {
>     set DG_TORTURE_OPTIONS $TORTURE_OPTIONS
> } else {
>     # It is theoretically beneficial to group all of the O2/O3 options together,
>     # as in many cases the compiler will generate identical executables for
>     # all of them--and the c-torture testsuite will skip testing identical
>     # executables multiple times.
>     # Also note that -finline-functions is explicitly included in one of the
>     # items below, even though -O3 is also specified, because some ports may
>     # choose to disable inlining functions by default, even when optimizing.
>     set DG_TORTURE_OPTIONS [list \
>         { -O0 } \
>         { -O1 } \
>         { -O2 } \
>         { -O3 -fomit-frame-pointer -funroll-loops -fpeel-loops
> -ftracer -finline-functions } \
>         { -O3 -g } \
>         { -Os } ]
>
>     if [check_effective_target_lto] {
>         # When having plugin test both slim and fat LTO and plugin/nonplugin
>         # path.
>         if [check_linker_plugin_available] {
>            set LTO_TORTURE_OPTIONS [list \
>               { -O2 -flto -fno-use-linker-plugin -flto-partition=none } \
>               { -O2 -flto -fuse-linker-plugin -fno-fat-lto-objects }
>            ]
>         } else {
>            set LTO_TORTURE_OPTIONS [list \
>               { -O2 -flto -flto-partition=none } \
>               { -O2 -flto }
>            ]
>         }
>
> so either TORTURE_OPTIONS is set or check_effective_target_lto doesn't work.
> The check does simply
>
>     return [check_no_compiler_messages lto object {
>         void foo (void) { }
>     } "-flto"]
>
> so I wonder what your excess errors are?  The check above should also
> leave traces
> in the testsuite log.  It might be that --disable-lto doesn't disable
> gcc -c -flto but just
> disables lto1 building though.

I checked and it works fine for me, --disable-lto disables LTO support
and  there's
no extra FAILs in dg-torture.exp.  The testsuite log has

Executing on host: /tmp/obj/gcc/xgcc -B/tmp/obj/gcc/
-fdiagnostics-plain-output  -flto -c -o lto10207.o lto10207.c
(timeout = 300)
spawn -ignore SIGHUP /tmp/obj/gcc/xgcc -B/tmp/obj/gcc/
-fdiagnostics-plain-output -flto -c -o lto10207.o lto10207.c^M
cc1: error: LTO support has not been enabled in this configuration^M
compiler exited with status 1

which causes no -flto to be used.

Richard.

>
> >
> > --
> > Steve