https://gcc.gnu.org/bugzilla/show_bug.cgi?id=121942
Bug ID: 121942
Summary: printed bool value is not what if-statement uses
Product: gcc
Version: 13.3.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: linasvepstas at gmail dot com
Target Milestone: ---
Multiple compiler versions affected. Different compilers behave differently,
but still badly.
A bool value is computed. The printed value is correct. When used in an
if-statement, it is incorrect. i.e. what is printed, and what is used, do not
match.
Full description in the cc file.
// Bug: boolean values seem to be mis-handled with -O2 optimization.
// Caution: yes, there are floats in this bug report. No, that's not
// "really" the problem, although they are entangled into it.
//
// The following attempts to compare vectors of floats.
// The compare is done by casting the floats to int64_t.
// Yes, there is reason to "hate this", but its not unusual.
// At any rate, that's not what this bug is about.
// The int64_t (and uint64_t)'s behave as expected.
// A bool is computed. The printed value of the bool is correct.
// Despite the bool being "true", the if-statement treats it as false.
// And not just once, but consistently.
//
// g++ -O2 insane-more-O2.cc -o insane-more-O2-bad -save-temps
// g++ -O1 insane-more-O2.cc -o insane-more-O2-good
//
// Offending compiler, linker, runtime loader:
// gcc (Ubuntu 13.3.0-6ubuntu2~24.04) 13.3.0
// GNU ld (GNU Binutils for Ubuntu) 2.42
// ldd (Ubuntu GLIBC 2.39-0ubuntu8.5) 2.39
//
// Also affected:
// gcc (Debian 12.2.0-14+deb12u1) 12.2.0
// GNU ld (GNU Binutils for Debian) 2.40
// ldd (Debian GLIBC 2.36-9+deb12u10) 2.36
