On Thu, 19 Oct 2023, Tamar Christina wrote:
> Hi All,
>
> As the testcase shows, when a PHI node dominates the loop there is no new
> definition inside the loop. As such there would be no PHI nodes to update.
>
> When we maintain LCSSA form we create an intermediate node in between the two
> loops to thread alongt the value. However later on when we update the second
> loop we don't have any PHI nodes to update and so adjust_phi_and_debug_stmts
> does nothing. This leaves us with an incorrect phi node. Normally this does
> nothing and just gets ignored. But in the case of the vUSE chain we end up
> corrupting the chain.
>
> As such whenever a PHI node's argument dominates the loop, we should remove
> the newly created PHI node after edge redirection.
>
> The one exception to this is when the loop has been versioned. In such cases
> the versioned loop may not use the value but the second loop can.
>
> When this happens and we add the loop guard unless the join block has the PHI
> it can't find the original value for use inside the guard block.
>
> The next refactoring in the series moves the formation of the guard block
> inside peeling itself. Here we have all the information and wouldn't
> need to re-create it later.
>
> Bootstrapped Regtested on aarch64-none-linux-gnu, x86_64-linux-gnu
> and no issues and issues in libgomp fixed.
>
> Ok for master?
OK.
Thanks,
Richard.
> Thanks,
> Tamar
>
> gcc/ChangeLog:
>
> PR tree-optimization/111860
> * tree-vect-loop-manip.cc (slpeel_tree_duplicate_loop_to_edge_cfg):
> Remove PHI nodes that dominate loop.
>
> gcc/testsuite/ChangeLog:
>
> PR tree-optimization/111860
> * gcc.dg/vect/pr111860.c: New test.
>
> --- inline copy of patch --
> diff --git a/gcc/testsuite/gcc.dg/vect/pr111860.c
> b/gcc/testsuite/gcc.dg/vect/pr111860.c
> new file mode 100644
> index
> 0000000000000000000000000000000000000000..36f0774601040418bc6b7f27c9425b2bf93b18cb
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/vect/pr111860.c
> @@ -0,0 +1,16 @@
> +/* { dg-do compile } */
> +
> +int optimize_path_n, optimize_path_d;
> +int *optimize_path_d_0;
> +extern void path_threeOpt( long);
> +void optimize_path() {
> + int i;
> + long length;
> + i = 0;
> + for (; i <= optimize_path_n; i++)
> + optimize_path_d = 0;
> + i = 0;
> + for (; i < optimize_path_n; i++)
> + length += optimize_path_d_0[i];
> + path_threeOpt(length);
> +}
> diff --git a/gcc/tree-vect-loop-manip.cc b/gcc/tree-vect-loop-manip.cc
> index
> 1f7779b9834c3aef3c6a993fab916224fab03147..db1d4f867ead5c6079cda3ff0d0870234d11e39d
> 100644
> --- a/gcc/tree-vect-loop-manip.cc
> +++ b/gcc/tree-vect-loop-manip.cc
> @@ -1633,6 +1633,21 @@ slpeel_tree_duplicate_loop_to_edge_cfg (class loop
> *loop, edge loop_exit,
> {
> tree new_arg = gimple_phi_arg (phi, 0)->def;
> new_phi_args.put (new_arg, gimple_phi_result (phi));
> +
> + if (TREE_CODE (new_arg) != SSA_NAME)
> + continue;
> + /* If the PHI node dominates the loop then we shouldn't create
> + a new LC-SSSA PHI for it in the intermediate block. Unless the
> + the loop has been versioned. If it has then we need the PHI
> + node such that later when the loop guard is added the original
> + dominating PHI can be found. */
> + basic_block def_bb = gimple_bb (SSA_NAME_DEF_STMT (new_arg));
> + if (loop == scalar_loop
> + && (!def_bb || !flow_bb_inside_loop_p (loop, def_bb)))
> + {
> + auto gsi = gsi_for_stmt (phi);
> + remove_phi_node (&gsi, true);
> + }
> }
>
> /* Copy the current loop LC PHI nodes between the original loop exit
>
>
>
>
>
--
Richard Biener <rguent...@suse.de>
SUSE Software Solutions Germany GmbH,
Frankenstrasse 146, 90461 Nuernberg, Germany;
GF: Ivo Totev, Andrew McDonald, Werner Knoblich; (HRB 36809, AG Nuernberg)
