[Bug sanitizer/112748] memmove(ptr, ptr, n) call optimized out even at -O0 with -fsanitize=undefined

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112748

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
           Keywords|                            |documentation
                 CC|                            |dodji at gcc dot gnu.org,
                   |                            |dvyukov at gcc dot gnu.org,
                   |                            |jakub at gcc dot gnu.org,
                   |                            |kcc at gcc dot gnu.org,
                   |                            |marxin at gcc dot gnu.org
     Ever confirmed|0                           |1
          Component|middle-end                  |sanitizer
   Last reconfirmed|                            |2023-11-29

--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> ---
Confirmed.  We fold all calls early after gimplification and folding is known
to also affect -O0.  This behavior is independent of sanitizing which happens
partly before and partly only after this folding takes place.

We also simplify 1 + 1 or x + 0 with -O0 or turn printf("%s", "Hello")
into puts("Hello") for example.

Documenting this behavior might be good.  Gating some of the simplifications
on optimization might be also reasonable.