On 27/04/2012, at 1:17 AM, Richard Guenther wrote:
> On Wed, Apr 25, 2012 at 8:06 AM, Maxim Kuvyrkov <ma...@codesourcery.com>
> wrote:
>
...
> +ppre_n_insert_for_speed_p (pre_expr expr, basic_block block,
> + unsigned int inserts_needed)
> +{
> + /* The more expensive EXPR is, the more we should be prepared to insert
> + in the predecessors of BLOCK to make EXPR fully redundant.
> + For now, only recognize AND, OR, XOR, PLUS and MINUS of a multiple-use
> + SSA_NAME with a constant as cheap. */
>
> the function implementation is odd. cost is always 1 when used, and
> both memory loads and calls are always cheap, but for example casts are not?
> Isn't
>
> return EDGE_COUNT (block->preds) * cost >= inserts_needed;
>
> always true? Or is inserts_needed not what it suggests?
It /almost/ is what it suggests. To account for the fact that inserts will not
benefit some of the paths (50% in the initial version of the patch, and a more
precise estimate in a latter version) we tell/lie ppre_n_insert_for_speed_p
that we need a greater number of the inserts (e.g., 2x the real number) that we
will perform.
>
> + /* Insert only if we can remove a later expression on a path
> + that we want to optimize for speed.
> + The phi node that we will be inserting in BLOCK is not free,
> + and inserting it for the sake of !optimize_for_speed
> successor
> + may cause regressions on the speed path. */
> + FOR_EACH_EDGE (succ, ei, block->succs)
> + {
> + if (bitmap_set_contains_value (PA_IN (succ->dest), val))
> + {
> + if (optimize_edge_for_speed_p (succ))
> + do_insertion = true;
> +
> + ++pa_succs;
> + }
> + }
>
> the change up to here looks good to me - can you factor out the command-line
> switch plus this optimize_edge_for_speed_p test into a separate patch
> (hereby approved)?
Attached is what I checked in after retesting on a fresh mainline. This part
of the patch by itself turns out to fix the bitmnp01 regression in what seems
to be a reliable way. Therefore, I'll mark PR38785 as fixed.
Thank you,
--
Maxim Kuvyrkov
CodeSourcery / Mentor Graphics
pr38785-2.ChangeLog
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pr38785-2.patch
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