Re: warning: unsequenced modification and access to 'sa_avail'

[Philipp <p.stephani2@gmail.com>]

> Am 27.03.2021 um 17:05 schrieb Jeffrey Walton <noloader@gmail.com>:
> 
> Hi Everyone,
> 
> I'm building Emacs 27.2 on the Apple M1 machine. I think the compiler
> is complaining about undefined behavior:
> 
>    sa_avail -= (size), alloca (size)
> 
> I think it is equivalent to something like this:
> 
>    data[i] = data[i++];
> 
> /usr/bin/clang -c -I/usr/local/include -DNDEBUG -Demacs  -I. -I.
> -I../lib -I../lib         -I/usr/local/include/libxml2
> -I/usr/local/include              -MMD -MF deps/doc.d -MP
> -I/usr/local/include -I/usr/local/include/p11-kit-1    -Wno-switch
> -Wno-pointer-sign -Wno-string-plus-int -Wno-unknown-attributes
> -Wno-initializer-overrides -Wno-tautological-compare
> -Wno-tautological-constant-out-of-range-compare -g2 -O2 -fno-common
> -arch arm64 -fPIC -pthread  doc.c
> /usr/bin/clang -c -I/usr/local/include -DNDEBUG -Demacs  -I. -I.
> -I../lib -I../lib         -I/usr/local/include/libxml2
> -I/usr/local/include              -MMD -MF deps/editfns.d -MP
> -I/usr/local/include -I/usr/local/include/p11-kit-1    -Wno-switch
> -Wno-pointer-sign -Wno-string-plus-int -Wno-unknown-attributes
> -Wno-initializer-overrides -Wno-tautological-compare
> -Wno-tautological-constant-out-of-range-compare -g2 -O2 -fno-common
> -arch arm64 -fPIC -pthread  editfns.c
> editfns.c:2063:18: warning: unsequenced modification and access to 'sa_avail'
>      [-Wunsequenced]
>    .deletions = SAFE_ALLOCA (del_bytes),
>                 ^
> ./lisp.h:4817:9: note: expanded from macro 'SAFE_ALLOCA'
>                           ? AVAIL_ALLOCA (size)                        \
>                             ^
> ./lisp.h:4812:38: note: expanded from macro 'AVAIL_ALLOCA'
> #define AVAIL_ALLOCA(size) (sa_avail -= (size), alloca (size))
>                                     ^
> 

This has already been fixed by commit 6a4ed891d84b1ca1e4d68a6de9dd374f1fadd971, which hasn't made it into the release though.