[Bug tree-optimization/77824] unreachable code in SLSR GIMPLE pass

[wschmidt at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77824

--- Comment #6 from Bill Schmidt <wschmidt at gcc dot gnu.org> ---
I've done some poking around, and I see copies showing up frequently in some of
GCC's own libraries, as well as in SPEC CPU2006 code.  With a patched compiler
to key on SSA_NAME for copies, I've seen that many of these copies are for
induction variables, though not all.  I have yet to find a case where handling
the copies in SLSR changes the code.

I'll plan to commit the obvious fix here.  It doesn't seem practical to try to
create a test case guaranteed to have copies in the code by the time we hit
SLSR, though.