https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94429
Bug ID: 94429
Summary: Bogus sequence point warning
Product: gcc
Version: 9.3.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: ofekshilon at gmail dot com
Target Milestone: ---
This code:
int main()
{
int a = 1;
a = ++a ;
}
built with -std=c++17 -Wall (or just -Wsequence-point)
gives:
<source>:4:5: warning: operation on 'a' may be undefined [-Wsequence-point]
4 | a = ++a ;
| ~~^~~~~
Since c++17 this is no longer undefined:
https://timsong-cpp.github.io/cppwp/n4659/expr.ass#1
Moreover, it seems that sometime ago the gcc team was aware of it:
https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html#index-Wsequence-point
"The C++17 standard will define the order of evaluation of operands in more
cases: in particular it requires that the right-hand side of an assignment be
evaluated before the left-hand side, so the above examples are no longer
undefined. But this option will still warn about them, to help people avoid
writing code that is undefined in C and earlier revisions of C++."
I (and others,
https://stackoverflow.com/questions/60937761/sequence-points-is-this-gcc-warning-a-bug)
consider this definitely a bug. When I'm writing in C++17 and need to produce
warning-free code, I don't expect to work around the compiler saying I should
write code that would be valid in other language versions.
