Re: [patch] Fix PR39976, sixtrack degradation

[Richard Guenther <richard dot guenther at gmail dot com>]

On Wed, May 13, 2009 at 8:15 PM, Michael Matz <matz@suse.de> wrote:
> Hi,
>
> inserting on back edges causes problems downstream by deficiencies in the
> later passes that can't deal with multiple BBs. ?So let's make life not as
> tough for them by trying to avoid that situation. ?We already detect some
> sitations in which surely a conflict (hence no coalescing and a copy)
> occurs, so we can as well detect some more situations.
>
> This fixes the particular problem in sixtrack where it now generates a
> single BB loop. ?I haven't verified that this also restores the
> performance fully, I would be grateful for somebody try this on powerpc
> (Luis?).
>
> Regstrapped without regressions on x86_64-linux. ?Okay?
>
>
> Ciao,
> Michael.
> --
> ? ? ? ?PR middle-end/39976
> ? ? ? ?* tree-outof-ssa.c (trivially_conflicts_p): New function.
> ? ? ? ?(insert_backedge_copies): Use it.
>
> Index: tree-outof-ssa.c
> ===================================================================
> --- tree-outof-ssa.c ? ?(Revision 147214)
> +++ tree-outof-ssa.c ? ?(Arbeitskopie)
> @@ -853,6 +853,47 @@ remove_ssa_form (bool perform_ter, struc
> ?}
>
>
> +/* Return true if we can determine that the SSA_NAMEs RESULT (a result
> + ? of a PHI node) and ARG (one of its arguments) conflict. ?Return false
> + ? otherwise, also when we simply aren't sure. ?*/
> +
> +static bool
> +trivially_conflicts_p (basic_block bb, tree result, tree arg)
> +{
> + ?use_operand_p use;
> + ?imm_use_iterator imm_iter;
> + ?gimple defa = SSA_NAME_DEF_STMT (arg);
> +
> + ?/* If ARG isn't defined in the same block it's too complicated for
> + ? ? our little mind. ?*/
> + ?if (gimple_bb (defa) != bb)
> + ? ?return false;
> +
> + ?FOR_EACH_IMM_USE_FAST (use, imm_iter, result)
> + ? ?{
> + ? ? ?gimple_stmt_iterator gsi;
> + ? ? ?gimple use_stmt = USE_STMT (use);
> + ? ? ?/* Now, if there's a use of RESULT that lies outside this basic block,
> + ? ? ? ?then there surely is a conflict with ARG. ?*/
> + ? ? ?if (gimple_bb (use_stmt) != bb)
> + ? ? ? return true;
> + ? ? ?if (gimple_code (use_stmt) == GIMPLE_PHI)
> + ? ? ? continue;
> + ? ? ?/* The use now is in a real stmt of BB, so if ARG was defined
> + ? ? ? ? in a PHI node (like RESULT) both conflict. ?*/
> + ? ? ?if (gimple_code (defa) == GIMPLE_PHI)
> + ? ? ? return true;
> + ? ? ?/* If the use of RESULT occurs after the definition of ARG,
> + ? ? ? ? the two conflict too. ?*/
> + ? ? ?for (gsi = gsi_start_bb (bb); gsi_stmt (gsi) != use_stmt; gsi_next (&gsi))
> + ? ? ? if (gsi_stmt (gsi) == defa)
> + ? ? ? ? return true;

Use gimple_uid here to check ordering.  They can be globally initialized
by renumber_gimple_stmt_uids().

Ok with that change.

Thanks,
Richard.

> + ? ?}
> +
> + ?return false;
> +}
> +
> +
> ?/* Search every PHI node for arguments associated with backedges which
> ? ?we can trivially determine will need a copy (the argument is either
> ? ?not an SSA_NAME or the argument has a different underlying variable
> @@ -892,7 +933,8 @@ insert_backedge_copies (void)
> ? ? ? ? ? ? ? ? needed. ?*/
> ? ? ? ? ? ? ?if ((e->flags & EDGE_DFS_BACK)
> ? ? ? ? ? ? ? ? ?&& (TREE_CODE (arg) != SSA_NAME
> - ? ? ? ? ? ? ? ? ? ? || SSA_NAME_VAR (arg) != result_var))
> + ? ? ? ? ? ? ? ? ? ? || SSA_NAME_VAR (arg) != result_var
> + ? ? ? ? ? ? ? ? ? ? || trivially_conflicts_p (bb, result, arg)))
> ? ? ? ? ? ? ? ?{
> ? ? ? ? ? ? ? ? ?tree name;
> ? ? ? ? ? ? ? ? ?gimple stmt, last = NULL;
>