https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98117
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |rsandifo at gcc dot gnu.org
--- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> ---
In fact there is alrady
/* Create: niters >> log2(vf) */
/* If it's known that niters == number of latch executions + 1 doesn't
overflow, we can generate niters >> log2(vf); otherwise we generate
(niters - vf) >> log2(vf) + 1 by using the fact that we know ratio
will be at least one. */
so we know about this "defect". The computation method translates easily
to the range case (unconditionally). Unfortunately for some 'degenerate'
cases where we arrive with const_vf == 1 we'll compute [1, 0] "ranges"
this way which ICEs in niter compute.
The question is whether we can construct cases we miscompile with such
large niter and VF == 1 (full SLP). As noted when I added niter_m1 all
uses of 'niter' would have to go away :/
For now I'm testing the "ugly"
diff --git a/gcc/tree-vect-loop-manip.c b/gcc/tree-vect-loop-manip.c
index 36179188f6d..36f218e7f6e 100644
--- a/gcc/tree-vect-loop-manip.c
+++ b/gcc/tree-vect-loop-manip.c
@@ -2034,13 +2034,21 @@ vect_gen_vector_loop_niters (loop_vec_info loop_vinfo,
tree niters,
niters_vector = force_gimple_operand (niters_vector, &stmts, true, var);
gsi_insert_seq_on_edge_immediate (pe, stmts);
/* Peeling algorithm guarantees that vector loop bound is at least ONE,
- we set range information to make niters analyzer's life easier. */
+ we set range information to make niters analyzer's life easier.
+ Note the number of latch iteration value can be TYPE_MAX_VALUE so
+ we have to represent the vector niter TYPE_MAX_VALUE + 1 >> log_vf.
*/
if (stmts != NULL && log_vf)
set_range_info (niters_vector, VR_RANGE,
- wi::to_wide (build_int_cst (type, 1)),
- wi::to_wide (fold_build2 (RSHIFT_EXPR, type,
- TYPE_MAX_VALUE (type),
- log_vf)));
+ wi::one (TYPE_PRECISION (type)),
+ /* ??? Avoid creating [1, 0]. */
+ const_vf == 1
+ ? wi::max_value (TYPE_PRECISION (type),
+ TYPE_SIGN (type))
+ : (wi::rshift (wi::max_value (TYPE_PRECISION (type),
+ TYPE_SIGN (type))
+ - (const_vf - 1),
+ exact_log2 (const_vf), TYPE_SIGN (type))
+ + 1));
}
*niters_vector_ptr = niters_vector;
*step_vector_ptr = step_vector;
