https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97603
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Component|tree-optimization |rtl-optimization
Last reconfirmed| |2020-10-28
Ever confirmed|0 |1
Status|UNCONFIRMED |NEW
--- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> ---
I guess it could be formulated as code-hoisting opportunity when we make
a - b (or b - a) anticipated on the edges from the a != b compare. What's
then missing is transforming
int tem = a - b;
if (a != b)
...
into
tem = a - b;
if (tem != 0)
but IIRC we essentially do the reverse transform via match.pd. Here
the main issue is that the GIMPLE IL doesn't reflect what targets
usually do, that is, flags registers are not modeled and instead we
branch on the actual compare rather than its outcome and a subtract
doesn't set flags.
Eventually this is sth for RTL if-conversion though where those details
are exposed.
