[gcc r14-5516] VECT: Clear LOOP_VINFO_USING_SELECT_VL_P when loop is not partial vectorized

[gcc r14-5516] VECT: Clear LOOP_VINFO_USING_SELECT_VL_P when loop is not partial vectorized

[Lehua Ding]

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.

Diff:
---
 gcc/testsuite/gcc.target/riscv/rvv/autovec/pr112554.c | 12 ++++++++++++
 gcc/tree-vect-loop.cc                                 | 13 +++++++++++++
 2 files changed, 25 insertions(+)

diff --git a/gcc/testsuite/gcc.target/riscv/rvv/autovec/pr112554.c b/gcc/testsuite/gcc.target/riscv/rvv/autovec/pr112554.c
new file mode 100644
index 00000000000..4afa7c2b15c
--- /dev/null
+++ b/gcc/testsuite/gcc.target/riscv/rvv/autovec/pr112554.c
@@ -0,0 +1,12 @@
+/* { dg-do compile } */
+/* { dg-options "-march=rv64gcv -mabi=lp64d -O3 --param=riscv-autovec-preference=fixed-vlmax" } */
+
+int a;
+void b() {
+  unsigned long c = 18446744073709551612UL;
+d:
+  --c;
+  a ^= c;
+  if (c)
+    goto d;
+}
diff --git a/gcc/tree-vect-loop.cc b/gcc/tree-vect-loop.cc
index fb8d999ee6b..3f59139cb01 100644
--- a/gcc/tree-vect-loop.cc
+++ b/gcc/tree-vect-loop.cc
@@ -2657,6 +2657,19 @@ vect_determine_partial_vectors_and_peeling (loop_vec_info loop_vinfo)
     = (!LOOP_VINFO_USING_PARTIAL_VECTORS_P (loop_vinfo)
        && need_peeling_or_partial_vectors_p);
 
+  /* We set LOOP_VINFO_USING_SELECT_VL_P as true before loop vectorization
+     analysis that we don't know whether the loop is vectorized by partial
+     vectors (More details see tree-vect-loop-manip.cc).
+
+     However, SELECT_VL vectorizaton style should only applied on partial
+     vectorization since SELECT_VL is the GIMPLE IR that calculates the
+     number of elements to be process for each iteration.
+
+     After loop vectorization analysis, Clear LOOP_VINFO_USING_SELECT_VL_P
+     if it is not partial vectorized loop.  */
+  if (!LOOP_VINFO_USING_PARTIAL_VECTORS_P (loop_vinfo))
+    LOOP_VINFO_USING_SELECT_VL_P (loop_vinfo) = false;
+
   return opt_result::success ();
 }