https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102681
--- Comment #21 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to Andrew Pinski from comment #14)
> Created attachment 51650 [details]
> Little more reduced
>
> So FRE is able to figure out for the following:
> # _20 = PHI <0(2), 1(3)>
> # const_upper_26 = PHI <const_upper_27(D)(2), _19(3)>
> ....
> # _30 = PHI <0(12), 1(13)>
> # const_upper_33 = PHI <const_upper_34(D)(12), _29(13)>
>
> That _30 is the same as _20 but not _26 is the same as _33 even though it
> does figure out that _19 and _29 are the same as _10. If it is able to
> figure that out, then things would just work.
>
> Richi,
> I assume FRE does not Value number default SSA names (non-parm) the same
> which is why this is happening is that correct?
The issue with CSE here is that with RPO VN I made unvisited vars
VARYING due to on-demand handling. While vn_visit_phis has special
handling for undefs the hashtable insert/lookup do not.
I am testing the following to rectify this (which then CSEs this PHI).
diff --git a/gcc/tree-ssa-sccvn.c b/gcc/tree-ssa-sccvn.c
index ae0172a143e..893b1d0ddaa 100644
--- a/gcc/tree-ssa-sccvn.c
+++ b/gcc/tree-ssa-sccvn.c
@@ -4499,7 +4499,12 @@ vn_phi_lookup (gimple *phi, bool backedges_varying_p)
tree def = PHI_ARG_DEF_FROM_EDGE (phi, e);
if (TREE_CODE (def) == SSA_NAME
&& (!backedges_varying_p || !(e->flags & EDGE_DFS_BACK)))
- def = SSA_VAL (def);
+ {
+ if (ssa_undefined_value_p (def, false))
+ def = VN_TOP;
+ else
+ def = SSA_VAL (def);
+ }
vp1->phiargs[e->dest_idx] = def;
}
vp1->type = TREE_TYPE (gimple_phi_result (phi));
@@ -4543,7 +4548,12 @@ vn_phi_insert (gimple *phi, tree result, bool
backedges_varying_p)
tree def = PHI_ARG_DEF_FROM_EDGE (phi, e);
if (TREE_CODE (def) == SSA_NAME
&& (!backedges_varying_p || !(e->flags & EDGE_DFS_BACK)))
- def = SSA_VAL (def);
+ {
+ if (ssa_undefined_value_p (def, false))
+ def = VN_TOP;
+ else
+ def = SSA_VAL (def);
+ }
vp1->phiargs[e->dest_idx] = def;
}
vp1->value_id = VN_INFO (result)->value_id;
