[Bug tree-optimization/112961] [13/14 Regression] middle-end Missed vectorization: failed to vectorize simple reduction max since GCC-13

[rguenth at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112961

--- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> ---
So in this case VN doesn't "fix" it because

Value numbering stmt = _29 = MAX_EXPR <_16, prephitmp_18>;
Setting value number of _29 to _29 (changed)
Making available beyond BB3 _29 for value _29
Value numbering stmt = prephitmp_23 = _29;
Setting value number of prephitmp_23 to _29 (changed)
...
Keeping eliminated stmt live as copy because of out-of-region uses

as the loop header is using this on the backedge and we are explicitly
excluding the latch block from processing to avoid CSE of PHIs(?).
I think including the latch block should be fine, but PR90402 is what
I added this special case for (the testcase still passes after reverting).