Re: testsuite requires LTO?

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

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.

>
> --
> Steve