VECT: Clear LOOP_VINFO_USING_SELECT_VL_P when loop is not partial vectorized

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.