On Thu, Jan 14, 2016 at 11:29 AM, Alan Lawrence <alan.lawre...@arm.com> wrote:
> (Previous message: https://gcc.gnu.org/ml/gcc-patches/2015-12/msg02159.html)
> On Sat, Dec 26, 2015 at 18:58 PM, Richard Biener <richard.guent...@gmail.com>
> wrote:
>
>>> I'm not sure whether adding a pass_copy_prop is the right thing here, but
>>> since
>>> loop-header-copying can create such opportunities, it seems good to take
>>> them!
>>
>> Aww. I'd rather have general infrastructure (like SCEV) deal with
>> those non-propagated copies.
>>
>> There are likely other missed propagation / folding opportunities
>> caused from partial peeling.
>>
>> Richard.
>
> I take your second point, but I am concerned that this leads to duplication of
> copy-propagation code throughout the compiler?
>
> However, this patch does that. Making analyze_initial_condition (alone) follow
> copies, is enough to solve my case of missed vectorization of pr65947-2.c;
> but I also used the routine in analyze_scalar_evolution_1, as it found copies
> to follow in both bootstrap and a significant number of testcases:
>
> c-c++-common/gomp/pr58472.c
> gcc.c-torture/execute/20000422-1.c
> gcc.c-torture/execute/20041213-2.c
> gcc.c-torture/execute/20100430-1.c
> gcc.c-torture/execute/pr49712.c
> gcc.c-torture/execute/pr58640.c
> gcc.dg/Warray-bounds-13.c
> gcc.dg/graphite/block-{1,5,6}.c
> gcc.dg/graphite/interchange-12.c
> gcc.dg/graphite/interchange-mvt.c
> gcc.dg/graphite/pr19910.c
> gcc.dg/graphite/uns-block-1.c
> gcc.dg/loop-unswitch-{2,4}.c
> gcc.dg/pr59670.c
> gcc.dg/torture/matrix-{1,2,3,4,5,6}.c
> gcc.dg/torture/pr24750-1.c
> gcc.dg/torture/transpose-{1,2,3,4,5,6}.c
>
> ...some of which were resolved to constants.
>
> (Of course, this approach is not as thorough as adding a pass_copy_prop. E.g.
> it
> does *not* enable vectorization of the inlined copy in pr65947-9.c.)
>
> Bootstrapped + check-gcc + check-g++ on ARM, AArch64, x86_64.
>
> gcc/ChangeLog:
>
> * tree-scalar-evolution.c (follow_copies): New.
> (analyze_initial_condition, analyze_scalar_evolution_1): Call
> previous.
> ---
> gcc/tree-scalar-evolution.c | 53
> ++++++++++++++++++++++++++++++---------------
> 1 file changed, 36 insertions(+), 17 deletions(-)
>
> diff --git a/gcc/tree-scalar-evolution.c b/gcc/tree-scalar-evolution.c
> index 9b33693..357eb8f 100644
> --- a/gcc/tree-scalar-evolution.c
> +++ b/gcc/tree-scalar-evolution.c
> @@ -1522,6 +1522,37 @@ analyze_evolution_in_loop (gphi *loop_phi_node,
> return evolution_function;
> }
>
> +/* While VAR is an SSA_NAME whose definition is a straight copy of another
> name,
> + or (perhaps via a degenerate phi) a constant, follows that definition.
> + Returns the constant, or the earliest SSA_NAME whose definition is neither
> + constant nor copy. */
> +
> +static tree
> +follow_copies (tree var)
> +{
> + while (TREE_CODE (var) == SSA_NAME)
> + {
> + gimple *def = SSA_NAME_DEF_STMT (var);
> + if (gphi *phi = dyn_cast <gphi *> (def))
> + {
> + tree rhs = degenerate_phi_result (phi);
> + /* Don't follow degenerate phi's of SSA_NAMES, that can break
> + loop-closed SSA form. */
> + if (rhs && is_gimple_min_invariant (rhs))
> + var = rhs;
> + break;
> + }
> + else if (gimple_assign_single_p (def)
> + && !gimple_vuse (def)
The vuse test is not necessary
> + && (gimple_assign_rhs_code (def) == SSA_NAME
> + || is_gimple_min_invariant (gimple_assign_rhs1 (def))))
and the is_gimple_min_invariant (rhs1) test is not sufficient if you
consider - (-INT_MIN) with -ftrapv for example.
I'd say you should do
else if (gassign *ass = dyn_cast <gassign *> (def))
{
tree_code code = gimple_assign_rhs_code (ass);
if (code == SSA_NAME
|| CONSTANT_CLASS_P (code))
var = gimple_assign_rhs1 (ass);
else
break;
}
> + var = gimple_assign_rhs1 (def);
> + else
> + break;
> + }
> + return var;
> +}
> +
> /* Given a loop-phi-node, return the initial conditions of the
> variable on entry of the loop. When the CCP has propagated
> constants into the loop-phi-node, the initial condition is
> @@ -1574,21 +1605,9 @@ analyze_initial_condition (gphi *loop_phi_node)
> if (init_cond == chrec_not_analyzed_yet)
> init_cond = chrec_dont_know;
>
> - /* During early loop unrolling we do not have fully constant propagated IL.
> - Handle degenerate PHIs here to not miss important unrollings. */
> - if (TREE_CODE (init_cond) == SSA_NAME)
> - {
> - gimple *def = SSA_NAME_DEF_STMT (init_cond);
> - if (gphi *phi = dyn_cast <gphi *> (def))
> - {
> - tree res = degenerate_phi_result (phi);
> - if (res != NULL_TREE
> - /* Only allow invariants here, otherwise we may break
> - loop-closed SSA form. */
> - && is_gimple_min_invariant (res))
> - init_cond = res;
> - }
> - }
> + /* We may not have fully constant propagated IL. Handle degenerate PHIs
> here
> + to not miss important early loop unrollings. */
> + init_cond = follow_copies (init_cond);
>
> if (dump_file && (dump_flags & TDF_SCEV))
> {
> @@ -1968,8 +1987,8 @@ analyze_scalar_evolution_1 (struct loop *loop, tree
> var, tree res)
> if (bb == NULL
> || !flow_bb_inside_loop_p (loop, bb))
> {
> - /* Keep the symbolic form. */
> - res = var;
> + /* Keep symbolic form, but look through obvious copies for constants.
> */
You're also looing for SSA names copied so the comment is sligntly wrong.
Ok with those changes.
Thanks,
Richard.
> + res = follow_copies (var);
> goto set_and_end;
> }
>
> --
> 1.9.1
>
