https://gcc.gnu.org/bugzilla/show_bug.cgi?id=121971
Bug ID: 121971
Summary: [15/16 Regression] Only warn about musttail on exotic
targets?
Product: gcc
Version: 15.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: bunk at stusta dot de
Target Milestone: ---
https://gcc.gnu.org/onlinedocs/gcc-15.1.0/gcc/Statement-Attributes.html#index-musttail-statement-attribute
...
If the compiler cannot generate a musttail tail call it reports an error. On
some targets, tail calls may not be supported at all.
...
In practice this looks like
https://buildd.debian.org/status/logs.php?pkg=protobuf&ver=3.21.12-12
(click on Maybe-Failed for the complete logs), and this is even an
understatement since ppc and 32-bit arm were already blacklisted:
https://sources.debian.org/src/protobuf/3.21.12-11/src/google/protobuf/port_def.inc#L257-L260
The 64-bit variants of x86 and arm seem to be properly working (and tend to
have the most relevant user bases), the current situation on more exotic
targets looks rather bleak.
The upstream fix is to use a whitelist instead:
https://github.com/protocolbuffers/protobuf/commit/719f3037032b2e952afe7fc49152cc4be38fa7a3
This bug is about the problem that not target-dependent code that wants to use
musttail currently needs such #ifdef's, which means in practice that there will
be some boilerplate #ifdef's pasted around widely.
It would be preferable if the compiler would only warn about musttail on more
exotic targets.
