Avoid division by zero via constant_multiple_p

With recent SLP vectorization patches I see RISC-V divison by zero
for gfortran.dg/matmul_10.f90 and others in get_group_load_store_type
which does

              && can_div_trunc_p (group_size
                                  * LOOP_VINFO_VECT_FACTOR (loop_vinfo) - gap,
                                  nunits, &tem, &remain)
              && (known_eq (remain, 0u)
                  || (constant_multiple_p (nunits, remain, &num)
                      && (vector_vector_composition_type (vectype, num,
                                                          &half_vtype)
                          != NULL_TREE))))
            overrun_p = false;

where for [2, 2] / [0, 2] the condition doesn't reflect what we
are trying to test - that, when remain is zero or, when non-zero,
nunits is a multiple of remain, we can avoid touching a gap via
loading smaller pieces and vector composition.

It isn't safe to change the known_eq to maybe_eq so instead
require known_ne (remain, 0u) before doing constant_multiple_p.
There's the corresponding code in vectorizable_load that's known
to have a latent similar issue, so sync that up as well.

	* tree-vect-stmts.cc (get_group_load_store_type): Check
	known_ne (remain, 0u) before doing constant_multiple_p.
	(vectorizable_load): Likewise.

diff --git a/gcc/tree-vect-stmts.cc b/gcc/tree-vect-stmts.cc
index 03c65f0958c63406750cad4fd8d6fb554efba6f2..72a29c0584b949a30bc44f20b108aeef950b3bb4 100644 (file)
--- a/gcc/tree-vect-stmts.cc
+++ b/gcc/tree-vect-stmts.cc
@@ -2126,7 +2126,8 @@ get_group_load_store_type (vec_info *vinfo, stmt_vec_info stmt_info,
                                  * LOOP_VINFO_VECT_FACTOR (loop_vinfo) - gap,
                                  nunits, &tem, &remain)
              && (known_eq (remain, 0u)
-                 || (constant_multiple_p (nunits, remain, &num)
+                 || (known_ne (remain, 0u)
+                     && constant_multiple_p (nunits, remain, &num)
                      && (vector_vector_composition_type (vectype, num,
                                                          &half_vtype)
                          != NULL_TREE))))
@@ -11519,7 +11520,8 @@ vectorizable_load (vec_info *vinfo,
                          {
                            /* remain should now be > 0 and < nunits.  */
                            unsigned num;
-                           if (constant_multiple_p (nunits, remain, &num))
+                           if (known_ne (remain, 0u)
+                               && constant_multiple_p (nunits, remain, &num))
                              {
                                tree ptype;
                                new_vtype