https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116563
Bug ID: 116563
Summary: Wtautological-compare for memcmp and friends
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: rv at rasmusvillemoes dot dk
Target Milestone: ---
I was a bit surprised to learn that a semi-obvious bug like
memcmp(counter2, counter2, 16)
is not flagged by -Wtautological-compare. The optimizer certainly knows that
the call can be replaced by a constant 0.
Would it be possible to include cases like strcmp(x, x), strncmp(x, x, *),
memcmp(x, x, *) etc. in -Wtautological-compare ? Or, given that
Wtautological-compare is in -Wall, maybe introduce another warning for such
cases (or teach -Wtautological-compare an optional level).
For most of these bugs I think it's fine to only warn when the two arguments
are exactly the same at the source level. So strcmp(s, s+0) doesn't need to
warn, and could provide an easy work-around for a false-positive warning.
