Re: [PATCH v3 02/16] vect: Change IV increment position to standard_iv_increment_position

Thu, 08 Oct 2026 06:24:11 -0700 

On 07/10/2026 09:52, Alfie Richards wrote:

On 06/10/2026 22:07, Tamar Christina wrote:



-----Original Message-----
From: Alfie Richards <[email protected]>
Sent: 17 September 2026 15:40
To: [email protected]
Cc: Alex Coplan <[email protected]>; Alice Carlotti
<[email protected]>; Andrea Pinski
<[email protected]>; Richard Biener <[email protected]>;
Tamar Christina <[email protected]>; Zdenek Dvorak <[email protected]>;
Robin Dapp <[email protected]>; Richard Sandiford
<[email protected]>; Kyrylo Tkachov <[email protected]>;
Alfie Richards <[email protected]>
Subject: [PATCH v3 02/16] vect: Change IV increment position to
standard_iv_increment_position

Change both vect_set_loop_controls_directly and
vect_update_ivs_after_vectorizer_for_early_breaks to use
standard_iv_increment_position.

This moves the IV increment to the end of the loop which is required for
situations where the IV increment is loop variant and calculated in the
loop body, such as HSSR.

gcc/ChangeLog:

    * tree-vect-loop-manip.cc (vect_set_loop_controls_directly):
    Use standard_iv_increment_position instead of
    vect_iv_increment_position .
    * tree-vect-loop.cc
    (vect_update_ivs_after_vectorizer_for_early_breaks):
    Likewise.



Patch is OK, but any reason not to change 
vect_set_loop_condition_partial_vectors_avx512
and vect_set_loop_condition_normal so all loop controls are 
materialized in the same place

consistently?

Nope, fair point, will change that, test, and push.


Update, it seems like there is good reason :)


I think PR 126301 also applies to 
vect_set_loop_condition_partial_vectors_avx512 and 
vect_set_loop_condition_normal which prevents this from working when peeled.


I will hold off pushing this patch until we work out how to solve this.

KR,
Alfie>

Thanks,
Alfie>

Thanks,
Tamar


---
  gcc/tree-vect-loop-manip.cc | 13 +++++--------
  gcc/tree-vect-loop.cc       |  3 +--
  2 files changed, 6 insertions(+), 10 deletions(-)

diff --git a/gcc/tree-vect-loop-manip.cc b/gcc/tree-vect-loop-manip.cc
index b54353399d9..78445e1f9aa 100644
--- a/gcc/tree-vect-loop-manip.cc
+++ b/gcc/tree-vect-loop-manip.cc
@@ -599,8 +599,8 @@ vect_set_loop_controls_directly (class loop *loop,
loop_vec_info loop_vinfo,
    tree index_before_incr, index_after_incr;
    gimple_stmt_iterator incr_gsi;
    bool insert_after;
-  edge exit_e = LOOP_VINFO_MAIN_EXIT (loop_vinfo);
-  vect_iv_increment_position (exit_e, &incr_gsi, &insert_after);
+  standard_iv_increment_position (loop, &incr_gsi, &insert_after);
+
    if (LOOP_VINFO_USING_DECREMENTING_IV_P (loop_vinfo))
      {

        /* Create an IV that counts down from niters_total and whose 
step

@@ -670,7 +670,6 @@ vect_set_loop_controls_directly (class loop *loop,
loop_vec_info loop_vinfo,

    tree zero_index = build_int_cst (compare_type, 0);
    tree test_index, test_limit, first_limit;
-  gimple_stmt_iterator *test_gsi;
    if (might_wrap_p)
      {

        /* In principle the loop should stop iterating once the 
incremented

@@ -709,7 +708,6 @@ vect_set_loop_controls_directly (class loop *loop,
loop_vec_info loop_vinfo,
                   nitems_total, adjust);

        test_limit = gimple_build (preheader_seq, MINUS_EXPR, 
compare_type,

                   test_limit, adjust);
-      test_gsi = &incr_gsi;

        /* Get a safe limit for the first iteration.  */
        if (nitems_skip)
@@ -740,7 +738,6 @@ vect_set_loop_controls_directly (class loop *loop,
loop_vec_info loop_vinfo,
        if (nitems_skip)
      test_limit = gimple_build (preheader_seq, PLUS_EXPR, compare_type,
                     test_limit, nitems_skip);
-      test_gsi = &loop_cond_gsi;

        first_limit = test_limit;
      }
@@ -749,7 +746,7 @@ vect_set_loop_controls_directly (class loop *loop,
loop_vec_info loop_vinfo,
       a demotion).  */
    gimple_seq test_seq = NULL;
    test_index = gimple_convert (&test_seq, compare_type, test_index);
-  gsi_insert_seq_before (test_gsi, test_seq, GSI_SAME_STMT);
+  gsi_insert_seq_after (&incr_gsi, test_seq, GSI_NEW_STMT);

    /* Provide a definition of each control in the group.  */
    tree next_ctrl = NULL_TREE;
@@ -858,14 +855,14 @@ vect_set_loop_controls_directly (class loop *loop,
loop_vec_info loop_vinfo,
        gimple_seq stmts = NULL;
        next_ctrl = vect_gen_while (&stmts, ctrl_type, test_index,
                        this_test_limit, "next_mask");
-      gsi_insert_seq_before (test_gsi, stmts, GSI_SAME_STMT);
+      gsi_insert_seq_after (&incr_gsi, stmts, GSI_SAME_STMT);
      }
        else
      {
        next_ctrl = make_temp_ssa_name (compare_type, NULL,
"next_len");

        gimple_seq seq = vect_gen_len (next_ctrl, test_index, 
this_test_limit,

                       length_limit);
-      gsi_insert_seq_before (test_gsi, seq, GSI_SAME_STMT);
+      gsi_insert_seq_after (&incr_gsi, seq, GSI_SAME_STMT);
      }

        vect_set_loop_control (loop, ctrl, init_ctrl, next_ctrl);
diff --git a/gcc/tree-vect-loop.cc b/gcc/tree-vect-loop.cc
index c7407098dc1..fdd224b50f9 100644
--- a/gcc/tree-vect-loop.cc
+++ b/gcc/tree-vect-loop.cc
@@ -11186,8 +11186,7 @@

vect_update_ivs_after_vectorizer_for_early_breaks (loop_vec_info 
loop_vinfo)

    /* Write the adjustments at the end of the iv increment.  */
    bool insert_after;
    gimple_stmt_iterator incr_gsi;
-  vect_iv_increment_position (LOOP_VINFO_MAIN_EXIT (loop_vinfo),
&incr_gsi,
-                  &insert_after);
+  standard_iv_increment_position (loop, &incr_gsi, &insert_after);

    if (insert_after)
      gsi_insert_seq_after (&incr_gsi, stmts, GSI_NEW_STMT);
--
2.43.0





























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