Sorry for wrong description on the log:

After this patch, the IR is:

  _36 = .SELECT_VL (ivtmp_34, POLY_INT_CST [4, 4]);
  _22 = (int) _36;
  vect_cst__21 = [vec_duplicate_expr] _22;



juzhe.zhong@rivai.ai
 
From: Juzhe-Zhong
Date: 2023-11-08 18:53
To: gcc-patches
CC: richard.sandiford; rguenther; kito.cheng; kito.cheng; Juzhe-Zhong
Subject: [PATCH] Middle-end: Fix bug of induction variable vectorization for RVV
PR: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112438
 
SELECT_VL result is not necessary always VF in non-final iteration.
 
Current GIMPLE IR is wrong:
 
# vect_vec_iv_.21_25 = PHI <_24(4), { 0, 1, 2, ... }(3)>
...
_24 = vect_vec_iv_.21_25 + { POLY_INT_CST [4, 4], ... };
 
After this patch which is correct for SELECT_VL:
 
# vect_vec_iv_.8_22 = PHI <_21(4), { 0, 1, 2, ... }(3)>
...
_35 = .SELECT_VL (ivtmp_33, POLY_INT_CST [4, 4]);
_21 = vect_vec_iv_.8_22 + { POLY_INT_CST [4, 4], ... };
 
kito, could you give more explanation ?
 
PR middle/112438
 
gcc/ChangeLog:
 
* tree-vect-loop.cc (vectorizable_induction): Fix bug.
 
gcc/testsuite/ChangeLog:
 
* gcc.target/riscv/rvv/autovec/pr112438.c: New test.
 
---
.../gcc.target/riscv/rvv/autovec/pr112438.c   | 35 +++++++++++++++++
gcc/tree-vect-loop.cc                         | 39 +++++++++++++++----
2 files changed, 67 insertions(+), 7 deletions(-)
create mode 100644 gcc/testsuite/gcc.target/riscv/rvv/autovec/pr112438.c
 
diff --git a/gcc/testsuite/gcc.target/riscv/rvv/autovec/pr112438.c b/gcc/testsuite/gcc.target/riscv/rvv/autovec/pr112438.c
new file mode 100644
index 00000000000..b326d56a52c
--- /dev/null
+++ b/gcc/testsuite/gcc.target/riscv/rvv/autovec/pr112438.c
@@ -0,0 +1,35 @@
+/* { dg-do compile } */
+/* { dg-options "-march=rv64gcv -mabi=lp64d -O3 -fno-vect-cost-model -ffast-math -fdump-tree-optimized-details" } */
+
+void
+foo (int n, int *__restrict in, int *__restrict out)
+{
+  for (int i = 0; i < n; i += 1)
+    {
+      out[i] = in[i] + i;
+    }
+}
+
+void
+foo2 (int n, float * __restrict in, 
+float * __restrict out)
+{
+  for (int i = 0; i < n; i += 1)
+    {
+      out[i] = in[i] + i;
+    }
+}
+
+void
+foo3 (int n, float * __restrict in, 
+float * __restrict out, float x)
+{
+  for (int i = 0; i < n; i += 1)
+    {
+      out[i] = in[i] + i* i;
+    }
+}
+
+/* We don't want to see vect_vec_iv_.21_25 + { POLY_INT_CST [4, 4], ... }.  */
+/* { dg-final { scan-tree-dump-not "\\+ \{ POLY_INT_CST" "optimized" } } */
+
diff --git a/gcc/tree-vect-loop.cc b/gcc/tree-vect-loop.cc
index a544bc9b059..3e103946168 100644
--- a/gcc/tree-vect-loop.cc
+++ b/gcc/tree-vect-loop.cc
@@ -10309,10 +10309,30 @@ vectorizable_induction (loop_vec_info loop_vinfo,
     new_name = step_expr;
   else
     {
+      gimple_seq seq = NULL;
+      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;  */
+   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);
+ }
       /* iv_loop is the loop to be vectorized. Generate:
  vec_step = [VF*S, VF*S, VF*S, VF*S]  */
-      gimple_seq seq = NULL;
-      if (SCALAR_FLOAT_TYPE_P (TREE_TYPE (step_expr)))
+      else if (SCALAR_FLOAT_TYPE_P (TREE_TYPE (step_expr)))
{
  expr = build_int_cst (integer_type_node, vf);
  expr = gimple_build (&seq, FLOAT_EXPR, TREE_TYPE (step_expr), expr);
@@ -10323,8 +10343,13 @@ vectorizable_induction (loop_vec_info loop_vinfo,
       expr, step_expr);
       if (seq)
{
-   new_bb = gsi_insert_seq_on_edge_immediate (pe, seq);
-   gcc_assert (!new_bb);
+   if (LOOP_VINFO_USING_SELECT_VL_P (loop_vinfo))
+     gsi_insert_seq_before (&si, seq, GSI_SAME_STMT);
+   else
+     {
+       new_bb = gsi_insert_seq_on_edge_immediate (pe, seq);
+       gcc_assert (!new_bb);
+     }
}
     }
@@ -10332,9 +10357,9 @@ vectorizable_induction (loop_vec_info loop_vinfo,
   gcc_assert (CONSTANT_CLASS_P (new_name)
      || TREE_CODE (new_name) == SSA_NAME);
   new_vec = build_vector_from_val (step_vectype, t);
-  vec_step = vect_init_vector (loop_vinfo, stmt_info,
-        new_vec, step_vectype, NULL);
-
+  vec_step
+    = vect_init_vector (loop_vinfo, stmt_info, new_vec, step_vectype,
+ LOOP_VINFO_USING_SELECT_VL_P (loop_vinfo) ? &si : NULL);
   /* Create the following def-use cycle:
      loop prolog:
-- 
2.36.3