[Bug middle-end/112554] [14 Regression] RISC-V ICE: verify_ssa failed with -O3 --param riscv-autovec-preference=fixed-vlmax

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112554

--- Comment #1 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The trunk branch has been updated by Lehua Ding <lhtin@gcc.gnu.org>:

https://gcc.gnu.org/g:fc6f7ab4e078aaf52c37739da73eb6416f5ec788

commit r14-5516-gfc6f7ab4e078aaf52c37739da73eb6416f5ec788
Author: Juzhe-Zhong <juzhe.zhong@rivai.ai>
Date:   Thu Nov 16 10:58:16 2023 +0800

    VECT: Clear LOOP_VINFO_USING_SELECT_VL_P when loop is not partial
vectorized

    This patch fixes ICE:
    https://godbolt.org/z/z8T6o6qov

    <source>: In function 'b':
    <source>:2:6: error: missing definition
        2 | void b() {
          |      ^
    for SSA_NAME: loop_len_8 in statement:
    _1 = -loop_len_8;
    during GIMPLE pass: vect
    <source>:2:6: internal compiler error: verify_ssa failed
    0x7f1b56331082 __libc_start_main
            ???:0
    Please submit a full bug report, with preprocessed source (by using
-freport-bug).
    Please include the complete backtrace with any bug report.
    See <https://gcc.gnu.org/bugs/> for instructions.
    Compiler returned: 1

    The root cause is we generate such IR in vectorization:

      _1 = -loop_len_8;
      vect_cst__11 = {_1, _1};
      _18 = vect_vec_iv_.6_14 + vect_cst__11;

    loop_len_8 is uninitialized value.

    The IR _18 = vect_vec_iv_.6_14 + vect_cst__11; is generated because of we
are adding induction variable with
    the result of SELECT_VL instead of VF.

    The code is:

      else if (LOOP_VINFO_USING_SELECT_VL_P (loop_vinfo))
        {
          /* When we're using loop_len produced by SELEC_VL, the non-final
             iterations are not always processing VF elements.  So vectorize
             induction variable instead of

               _21 = vect_vec_iv_.6_22 + { VF, ... };

             We should generate:

               _35 = .SELECT_VL (ivtmp_33, VF);
               vect_cst__22 = [vec_duplicate_expr] _35;
               _21 = vect_vec_iv_.6_22 + vect_cst__22;  */
          gcc_assert (!slp_node);
          gimple_seq seq = NULL;
          vec_loop_lens *lens = &LOOP_VINFO_LENS (loop_vinfo);
          tree len = vect_get_loop_len (loop_vinfo, NULL, lens, 1, vectype, 0,
0);
          expr = force_gimple_operand (fold_convert (TREE_TYPE (step_expr),
                                                     unshare_expr (len)),
                                       &seq, true, NULL_TREE);
          new_name = gimple_build (&seq, MULT_EXPR, TREE_TYPE (step_expr),
expr,
                                   step_expr);
          gsi_insert_seq_before (&si, seq, GSI_SAME_STMT);
          step_iv_si = &si;
        }

    LOOP_VINFO_USING_SELECT_VL_P is set before loop vectorization analysis so
we don't know whether it is partial
    vectorization or not but the induction variable depends on SELECT_VL_P is
true.

    So update SELECT_VL_P as false when it is not partial vectorization.

            PR middle-end/112554

    gcc/ChangeLog:

            * tree-vect-loop.cc (vect_determine_partial_vectors_and_peeling):
            Clear SELECT_VL_P for non-partial vectorization.

    gcc/testsuite/ChangeLog:

            * gcc.target/riscv/rvv/autovec/pr112554.c: New test.