On Thu, Jan 26, 2017 at 11:04 AM, Jan Hubicka <hubi...@ucw.cz> wrote:
>> > + if (!contains_hot_bb && speed_p)
>> > + contains_hot_bb |= optimize_bb_for_speed_p (bb);
>> > +
>>
>> Hmm, but you are also counting the destination of the threading here
>> which we will
>> not duplicate. Shouldn't this be under the if (j < path_length - 1)
>> conditional so we
>> look for hot BBs we are actually duplicating only (similar restrictions
>> apply to
>> path[0]?).
>
> Aha, you are right. I am re-testing updated patch (it also solves the PR)
What about j == 0? We don't duplicate that block either.
> Honza
>
> Index: tree-ssa-threadbackward.c
> ===================================================================
> --- tree-ssa-threadbackward.c (revision 244732)
> +++ tree-ssa-threadbackward.c (working copy)
> @@ -159,6 +159,7 @@ profitable_jump_thread_path (vec<basic_b
> bool threaded_through_latch = false;
> bool multiway_branch_in_path = false;
> bool threaded_multiway_branch = false;
> + bool contains_hot_bb = false;
>
> /* Count the number of instructions on the path: as these instructions
> will have to be duplicated, we will not record the path if there
> @@ -168,6 +169,9 @@ profitable_jump_thread_path (vec<basic_b
> {
> basic_block bb = (*path)[j];
>
> + if (!contains_hot_bb && speed_p && j < path_length - 1)
> + contains_hot_bb |= optimize_bb_for_speed_p (bb);
> +
> /* Remember, blocks in the path are stored in opposite order
> in the PATH array. The last entry in the array represents
> the block with an outgoing edge that we will redirect to the
> @@ -311,7 +315,11 @@ profitable_jump_thread_path (vec<basic_b
> return NULL;
> }
>
> - if (speed_p && optimize_edge_for_speed_p (taken_edge))
> + /* Threading is profitable if the path duplicated is hot but also
> + in a case we separate cold path from hot path and permit optimization
> + of the hot path later. Be on the agressive side here. In some
> testcases,
> + as in PR 78407 this leads to noticeable improvements. */
> + if (speed_p && (optimize_edge_for_speed_p (taken_edge) || contains_hot_bb))
> {
> if (n_insns >= PARAM_VALUE (PARAM_MAX_FSM_THREAD_PATH_INSNS))
> {
