Re: [PATCH] middle-end: don't keep .MEM guard nodes for PHI nodes who dominate loop [PR111860]

[Richard Biener <rguenther@suse.de>]

On Fri, 20 Oct 2023, Tamar Christina wrote:

> Hi All,
> 
> The previous patch tried to remove PHI nodes that dominated the first loop,
> however the correct fix is to only remove .MEM nodes.
> 
> This patch thus makes the condition a bit stricter and only tries to remove
> MEM phi nodes.
> 
> I couldn't figure out a way to easily determine if a particular PHI is vUSE
> related, so the patch does:
> 
> 1. check if the definition is a vDEF and not defined in main loop.
> 2. check if the definition is a PHI and not defined in main loop. 
> 3. check if the definition is a default definition.
> 
> For no 2 and 3 we may misidentify the PHI, in both cases the value is defined
> outside of the loop version block which also makes it ok to remove.
> 
> Bootstrapped Regtested on aarch64-none-linux-gnu, powerpc64le-unknown-linux-gnu,
> x86_64-none-linux-gnu and no issues.
> 
> Tested all default testsuites.
> 
> Ok for master?
> 
> Thanks,
> Tamar
> 
> gcc/ChangeLog:
> 
> 	PR tree-optimization/111860
> 	* tree-vect-loop-manip.cc (slpeel_tree_duplicate_loop_to_edge_cfg):
> 	Drop .MEM nodes only.
> 
> gcc/testsuite/ChangeLog:
> 
> 	PR tree-optimization/111860
> 	* gcc.dg/vect/pr111860-2.c: New test.
> 	* gcc.dg/vect/pr111860-3.c: New test.
> 
> --- inline copy of patch -- 
> diff --git a/gcc/testsuite/gcc.dg/vect/pr111860-2.c b/gcc/testsuite/gcc.dg/vect/pr111860-2.c
> new file mode 100644
> index 0000000000000000000000000000000000000000..07f64ffb5318c9d7817d46802d123cc9a2d65ec9
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/vect/pr111860-2.c
> @@ -0,0 +1,17 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O -fno-tree-sink -ftree-vectorize" } */
> +int buffer_ctrl_ctx_0, buffer_ctrl_p1, buffer_ctrl_cmd;
> +
> +int
> +buffer_ctrl (long ret, int i)
> +{
> +  switch (buffer_ctrl_cmd)
> +    {
> +    case 1:
> +      buffer_ctrl_ctx_0 = 0;
> +      for (; i; i++)
> +	if (buffer_ctrl_p1)
> +	  ret++;
> +    }
> +  return ret;
> +}
> diff --git a/gcc/testsuite/gcc.dg/vect/pr111860-3.c b/gcc/testsuite/gcc.dg/vect/pr111860-3.c
> new file mode 100644
> index 0000000000000000000000000000000000000000..07f64ffb5318c9d7817d46802d123cc9a2d65ec9
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/vect/pr111860-3.c
> @@ -0,0 +1,17 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O -fno-tree-sink -ftree-vectorize" } */
> +int buffer_ctrl_ctx_0, buffer_ctrl_p1, buffer_ctrl_cmd;
> +
> +int
> +buffer_ctrl (long ret, int i)
> +{
> +  switch (buffer_ctrl_cmd)
> +    {
> +    case 1:
> +      buffer_ctrl_ctx_0 = 0;
> +      for (; i; i++)
> +	if (buffer_ctrl_p1)
> +	  ret++;
> +    }
> +  return ret;
> +}
> 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..fc55278e63f7a48943fdc32c5e207110cf14507e 100644
> --- a/gcc/tree-vect-loop-manip.cc
> +++ b/gcc/tree-vect-loop-manip.cc
> @@ -1626,13 +1626,33 @@ slpeel_tree_duplicate_loop_to_edge_cfg (class loop *loop, edge loop_exit,
>  	  edge temp_e = redirect_edge_and_branch (exit, new_preheader);
>  	  flush_pending_stmts (temp_e);
>  	}
> -
>        /* Record the new SSA names in the cache so that we can skip materializing
>  	 them again when we fill in the rest of the LCSSA variables.  */
>        for (auto phi : new_phis)
>  	{
>  	  tree new_arg = gimple_phi_arg (phi, 0)->def;
>  	  new_phi_args.put (new_arg, gimple_phi_result (phi));

don't you want to skip this as well?

> +
> +	  if (!SSA_VAR_P (new_arg))
> +	    continue;
> +	  /* If the PHI MEM node dominates the loop then we shouldn't create
> +	      a new LC-SSSA PHI for it in the intermediate block.   */
> +	  gimple *def_stmt = SSA_NAME_DEF_STMT (new_arg);
> +	  basic_block def_bb = gimple_bb (def_stmt);
> +	  /* A MEM phi that consitutes a new DEF for the vUSE chain can either
> +	     be a .VDEF or a PHI that operates on MEM.  */
> +	  if (((gimple_vdef (def_stmt) || is_a <gphi *> (def_stmt))
> +		  /* And said definition must not be inside the main loop.  */
> +	       && (!def_bb || !flow_bb_inside_loop_p (loop, def_bb)))
> +	      /* Or we must be a parameter.  In the last two cases we may remove
> +		 a non-MEM PHI node, but since they dominate both loops the
> +		 removal is unlikely to cause trouble as the exits must already
> +		 be using them.  */
> +	      || SSA_NAME_IS_DEFAULT_DEF (new_arg))
> +	    {
> +	      auto gsi = gsi_for_stmt (phi);
> +	      remove_phi_node (&gsi, true);
> +	    }

May I suggest the simpler

          gimple *def;
	  if (virtual_operand_p (new_arg)
              && (SSA_NAME_IS_DEFAULT_DEF (new_arg)
                  || !flow_bb_inside_loop_p (loop,
				gimple_bb (SSA_NAME_DEF_STMT (new_arg))))
	    {
> +           auto gsi = gsi_for_stmt (phi);
> +           remove_phi_node (&gsi, true);
            }

?

OK with that change.

Richard.