https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98848
--- Comment #6 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
So what about punting if the lhs of the possible over_widen pattern is a PHI on
loop header?
--- gcc/tree-vect-patterns.c.jj 2021-01-04 10:25:38.650235896 +0100
+++ gcc/tree-vect-patterns.c 2021-02-01 10:13:51.755008757 +0100
@@ -1579,6 +1579,20 @@ vect_recog_over_widening_pattern (vec_in
tree type = TREE_TYPE (lhs);
tree_code code = gimple_assign_rhs_code (last_stmt);
+ /* Punt if lhs might be used in a reduction. */
+ if (loop_vec_info loop_vinfo = dyn_cast<loop_vec_info> (vinfo))
+ {
+ use_operand_p use_p;
+ imm_use_iterator iter;
+ FOR_EACH_IMM_USE_FAST (use_p, iter, lhs)
+ {
+ gimple *use_stmt = USE_STMT (use_p);
+ if (gimple_code (use_stmt) == GIMPLE_PHI
+ && gimple_bb (use_stmt) == LOOP_VINFO_LOOP (loop_vinfo)->header)
+ return NULL;
+ }
+ }
+
/* Keep the first operand of a COND_EXPR as-is: only the other two
operands are interesting. */
unsigned int first_op = (code == COND_EXPR ? 2 : 1);
doesn't regress any vect.exp=*over-widen* tests and let's this testcase be
vectorized.
