https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80620
--- Comment #7 from Richard Biener <rguenth at gcc dot gnu.org> ---
Now needs sth before r247596 to reproduce.
The whole
PRE_EXPR_NARY (expr) = newnary;
constant = fully_constant_expression (expr);
PRE_EXPR_NARY (expr) = nary;
if (constant != expr)
{
/* For non-CONSTANTs we have to make sure we can eventually
insert the expression. Which means we need to have a
leader for it. */
if (constant->kind != CONSTANT)
{
/* Do not allow simplifications to non-constants over
backedges as this will likely result in a loop PHI node
to be inserted and increased register pressure.
See PR77498 - this avoids doing predcoms work in
a less efficient way. */
if (find_edge (pred, phiblock)->flags & EDGE_DFS_BACK)
;
else
{
unsigned value_id = get_expr_value_id (constant);
constant = find_leader_in_sets (value_id, set1, set2,
AVAIL_OUT (pred));
if (constant)
return constant;
mitigates the fact that
tree result = vn_nary_op_lookup_pieces (newnary->length,
newnary->opcode,
newnary->type,
&newnary->op[0],
&nary);
if (result && is_gimple_min_invariant (result))
return get_or_alloc_expr_for_constant (result);
doesn't allow SSA name result to prevail here. That is vn_nary_simplify
also just looks up the expr now even if not simplified. It also gets
fed leaders which are not necessarily final values and thus do not have
range-info cleared.
The SCCVN band-aid to clear SSA_NAME_RANGE_INFO doesn't apply here because
nothing is value-numbered to a.4_4 besides itself. But phi-translation
effectively value-numbers an expression to it.
