regexec.c: recent commit triggers new build-time warning

[jkeenan]

At v5.37.1-53-g431ea43db2 (committed Fri Jul 1 21:34:26 2022 -0600) I am observing these build-time warnings when compiling perl on FreeBSD-12 using clang10 as the compiler.

regexec.c:10165:31: warning: comparison of integers of different signs: 'PERL_UINT_FAST8_T' (aka 'unsigned int') and 'PERL_INT_FAST8_T' (aka 'int') [-Wsign-compare]
                for (i = 0; i < Binfo.count; i++) {
                            ~ ^ ~~~~~~~~~~~
regexec.c:10202:27: warning: comparison of integers of different signs: 'PERL_UINT_FAST8_T' (aka 'unsigned int') and 'PERL_INT_FAST8_T' (aka 'int') [-Wsign-compare]
            for (i = 0; i < Binfo.count; i++) {
                        ~ ^ ~~~~~~~~~~~

I was not getting these build-time warnings as recently as v5.37.1-29-gc25af7d977 (committed June 27). (At that commit, I was only getting the -Wunused-function warning previously reported in #19877.)

What is puzzling is that the statements in regexec.c at which the warnings are being emitted have been in blead for several years.

bb3825626ed (Karl Williamson          2020-11-13 09:38:21 -0700 10165)                 for (i = 0; i < Binfo.count; i++) {

commit bb3825626ed2b1217a2ac184eff66d0d4ed6e070
Author:     Karl Williamson <khw@cpan.org>
AuthorDate: Fri Nov 13 09:38:21 2020 -0700
Commit:     Karl Williamson <khw@cpan.org>
CommitDate: Sat Dec 19 21:36:46 2020 -0700

    regexec.c: Revamp S_setup_EXACTISH_ST() loop end conditions

So some very recent commit must have triggered the emission of these warnings.

[jkeenan]

Bisecting with this invocation:

~/bin/perl/identify-build-transitions \
        --compiler=clang \
        --gitdir="$GIT_WORKDIR/perl2" \
        --branch=blead \
        --first=c25af7d9772eae07700757f7061ca84e56c5c058 \
        --last=431ea43db26622d369b66e8ebcbf5abb1b899c0d \
        --configure_command='sh ./Configure -des -Dusedevel -Duseithreads -Dcc=clang 1>/dev/null 2>&1' \
        --probe=warning \
        --verbose

... indicates that the warnings first began to be emitted (on FreeBSD-12) at this commit:

commit 6e37db9b2eefdb70c52184da55586fe1cae6cffc
Author:     Karl Williamson <khw@cpan.org>
AuthorDate: Fri Jul 1 14:30:13 2022 -0600
Commit:     Karl Williamson <khw@cpan.org>
CommitDate: Fri Jul 1 14:32:31 2022 -0600

    regexec.c: Avoid compiler msgs

@khwilliamson, can you take a look?

[khwilliamson]

Try smoke-me/khw-comparison branch

[jkeenan]

Try smoke-me/khw-comparison branch

That looks good; please merge. Thanks.