https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68576
--- Comment #5 from bin.cheng <amker.cheng at gmail dot com> ---
The type conversion comses from lim, below code:
/* In case this is a stmt that is not unconditionally executed
when the target loop header is executed and the stmt may
invoke undefined integer or pointer overflow rewrite it to
unsigned arithmetic. */
if (is_gimple_assign (stmt)
&& INTEGRAL_TYPE_P (TREE_TYPE (gimple_assign_lhs (stmt)))
&& TYPE_OVERFLOW_UNDEFINED (TREE_TYPE (gimple_assign_lhs (stmt)))
&& arith_code_with_undefined_signed_overflow
(gimple_assign_rhs_code (stmt))
&& (!ALWAYS_EXECUTED_IN (bb)
|| !(ALWAYS_EXECUTED_IN (bb) == level
|| flow_loop_nested_p (ALWAYS_EXECUTED_IN (bb), level))))
gsi_insert_seq_on_edge (e, rewrite_to_defined_overflow (stmt));
Once it's introduced, SCEV can't resolve it but assume possible overflow.
By mannually disabling lim pass, SCEV works as expected and now outer loop can
be parallelized.
