On Fri, 1 Apr 2022, Martin Jambor wrote:
> Hi,
>
> PRs 68930 and 92497 show that when IPA-CP figures out constants in
> aggregate parameters or when passed by reference but the loads happen
> in an inlined function the information is lost. This happens even
> when the inlined function itself was known to have - or even cloned to
> have - such constants in incoming parameters because the transform
> phase of IPA passes is not run on them. See discussion in the bugs
> for reasons why.
>
> Honza suggested that we can plug the results of IPA-CP analysis into
> value numbering, so that FRE can figure out that some loads fetch
> known constants. This is what this patch attempts to do.
>
> Although I spent quite some time reading tree-sccvn.c, it is complex
> enough that I am sure I am not aware of various caveats and so I would
> not be terribly surprised if there were some issues with my approach
> that I am not aware of. Nevertheless, it seems to work well for simple
> cases and even passes bootstrap and testing (and LTO bootstrap) on
> x86_64-linux.
>
> I have experimented a little with using this approach instead of the
> function walking parts of the IPA-CP transformation phase. This would
> mean that the known-constants would not participate in the passes after
> IPA but before FRE - which are not many but there is a ccp and fwprop
> pass among others. For simple testcases like
> gcc/testsuite/gcc.dg/ipa/ipcp-agg-*.c, it makes not assembly difference
> at all.
>
> What do you think?
Comments below
> Martin
>
>
> gcc/ChangeLog:
>
> 2022-03-30 Martin Jambor <mjam...@suse.cz>
>
> PR ipa/68930
> PR ipa/92497
> * ipa-prop.cc (ipcp_get_aggregate_const): New function.
> (ipcp_transform_function): Do not deallocate transformation info.
> * ipa-prop.h (ipcp_get_aggregate_const): Declare.
> * tree-ssa-sccvn.cc: Include alloc-pool.h, symbol-summary.h and
> ipa-prop.h.
> (vn_reference_lookup_2): When hitting default-def vuse, query
> IPA-CP transformation info for any known constants.
>
> gcc/testsuite/ChangeLog:
>
> 2022-03-30 Martin Jambor <mjam...@suse.cz>
>
> PR ipa/68930
> PR ipa/92497
> * gcc.dg/ipa/pr92497-1.c: New test.
> * gcc.dg/ipa/pr92497-2.c: Likewise.
> ---
> gcc/ipa-prop.cc | 43 ++++++++++++++++++++++++----
> gcc/ipa-prop.h | 2 ++
> gcc/testsuite/gcc.dg/ipa/pr92497-1.c | 26 +++++++++++++++++
> gcc/testsuite/gcc.dg/ipa/pr92497-2.c | 26 +++++++++++++++++
> gcc/tree-ssa-sccvn.cc | 35 +++++++++++++++++++++-
> 5 files changed, 126 insertions(+), 6 deletions(-)
> create mode 100644 gcc/testsuite/gcc.dg/ipa/pr92497-1.c
> create mode 100644 gcc/testsuite/gcc.dg/ipa/pr92497-2.c
>
> diff --git a/gcc/ipa-prop.cc b/gcc/ipa-prop.cc
> index e55fe2776f2..a73a5d9ec1d 100644
> --- a/gcc/ipa-prop.cc
> +++ b/gcc/ipa-prop.cc
> @@ -5748,6 +5748,44 @@ ipcp_modif_dom_walker::before_dom_children
> (basic_block bb)
> return NULL;
> }
>
> +/* If IPA-CP discovered a constant in parameter PARM at OFFSET of a given
> SIZE
> + - whether passed by reference or not is given by BY_REF - return that
> + constant. Otherwise return NULL_TREE. */
> +
> +tree
> +ipcp_get_aggregate_const (tree parm, bool by_ref,
> + HOST_WIDE_INT offset, HOST_WIDE_INT size)
I'd prefer to pass in the function decl or struct function or
cgraph node.
> +{
> + cgraph_node *cnode = cgraph_node::get (current_function_decl);
> +
> + ipa_agg_replacement_value *aggval = ipa_get_agg_replacements_for_node
> (cnode);
> + if (!aggval)
> + return NULL_TREE;
> +
> + int index = 0;
> + for (tree p = DECL_ARGUMENTS (current_function_decl);
> + p != parm; p = DECL_CHAIN (p))
> + {
> + index++;
> + if (!p)
> + return NULL_TREE;
> + }
> +
> + ipa_agg_replacement_value *v;
> + for (v = aggval; v; v = v->next)
> + if (v->index == index
> + && v->offset == offset)
> + break;
> + if (!v
> + || v->by_ref != by_ref
> + || maybe_ne (tree_to_poly_int64 (TYPE_SIZE (TREE_TYPE (v->value))),
> + size))
> + return NULL_TREE;
two linear searches here - ugh. I wonder if we should instead
pre-fill a hash-map from PARM_DECL to a ipa_agg_replacement_value *
vector sorted by offset which we can binary search? That could be
done once when starting value-numbering (not on regions). Is
there any reason the data structure is as it is? It seems that
even ipcp_modif_dom_walker::before_dom_children will do a linear
walk and ipa_get_param_decl_index_1 also linearly walks parameters.
That looks highly sub-optimal to me, it's also done for each
mention of a parameter.
> + return v->value;
> +}
> +
> +
> /* Return true if we have recorded VALUE and MASK about PARM.
> Set VALUE and MASk accordingly. */
>
> @@ -6055,11 +6093,6 @@ ipcp_transform_function (struct cgraph_node *node)
> free_ipa_bb_info (bi);
> fbi.bb_infos.release ();
>
> - ipcp_transformation *s = ipcp_transformation_sum->get (node);
> - s->agg_values = NULL;
> - s->bits = NULL;
> - s->m_vr = NULL;
> -
> vec_free (descriptors);
> if (cfg_changed)
> delete_unreachable_blocks_update_callgraph (node, false);
> diff --git a/gcc/ipa-prop.h b/gcc/ipa-prop.h
> index 553adfc9f35..aa6fcb522ac 100644
> --- a/gcc/ipa-prop.h
> +++ b/gcc/ipa-prop.h
> @@ -1181,6 +1181,8 @@ void ipa_dump_param (FILE *, class ipa_node_params
> *info, int i);
> void ipa_release_body_info (struct ipa_func_body_info *);
> tree ipa_get_callee_param_type (struct cgraph_edge *e, int i);
> bool ipcp_get_parm_bits (tree, tree *, widest_int *);
> +tree ipcp_get_aggregate_const (tree parm, bool by_ref,
> + HOST_WIDE_INT offset, HOST_WIDE_INT size);
> bool unadjusted_ptr_and_unit_offset (tree op, tree *ret,
> poly_int64 *offset_ret);
>
> diff --git a/gcc/testsuite/gcc.dg/ipa/pr92497-1.c
> b/gcc/testsuite/gcc.dg/ipa/pr92497-1.c
> new file mode 100644
> index 00000000000..eb8f2e75fd0
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/ipa/pr92497-1.c
> @@ -0,0 +1,26 @@
> +/* { dg-do run } */
> +/* { dg-options "-O2 -fno-early-inlining" } */
> +
> +struct a {int a;};
> +static int //__attribute__ ((noinline))
> +foo (struct a a)
> +{
> + if (!__builtin_constant_p (a.a))
> + __builtin_abort ();
> + return a.a;
> +}
> +
> +static int __attribute__ ((noinline))
> +bar (struct a a)
> +{
> + return foo(a);
> +}
> +
> +volatile int r;
> +
> +int main()
> +{
> + struct a a={1};
> + r = bar (a);
> + return 0;
> +}
> diff --git a/gcc/testsuite/gcc.dg/ipa/pr92497-2.c
> b/gcc/testsuite/gcc.dg/ipa/pr92497-2.c
> new file mode 100644
> index 00000000000..56e611df8f9
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/ipa/pr92497-2.c
> @@ -0,0 +1,26 @@
> +/* { dg-do run } */
> +/* { dg-options "-O2 -fno-early-inlining -fno-ipa-sra" } */
> +
> +struct a {int a;};
> +static int //__attribute__ ((noinline))
> +foo (struct a *a)
> +{
> + if (!__builtin_constant_p (a->a))
> + __builtin_abort ();
> + return a->a;
> +}
> +
> +static int __attribute__ ((noinline))
> +bar (struct a *a)
> +{
> + return foo(a);
> +}
> +
> +volatile int r;
> +
> +int main()
> +{
> + struct a a={1};
> + r = bar (&a);
> + return 0;
> +}
> diff --git a/gcc/tree-ssa-sccvn.cc b/gcc/tree-ssa-sccvn.cc
> index 66b4fc21f5b..da558055054 100644
> --- a/gcc/tree-ssa-sccvn.cc
> +++ b/gcc/tree-ssa-sccvn.cc
> @@ -74,6 +74,9 @@ along with GCC; see the file COPYING3. If not see
> #include "ipa-modref-tree.h"
> #include "ipa-modref.h"
> #include "tree-ssa-sccvn.h"
> +#include "alloc-pool.h"
> +#include "symbol-summary.h"
> +#include "ipa-prop.h"
>
> /* This algorithm is based on the SCC algorithm presented by Keith
> Cooper and L. Taylor Simpson in "SCC-Based Value numbering"
> @@ -2273,7 +2276,7 @@ vn_walk_cb_data::push_partial_def (pd_data pd,
> with the current VUSE and performs the expression lookup. */
>
> static void *
> -vn_reference_lookup_2 (ao_ref *op ATTRIBUTE_UNUSED, tree vuse, void *data_)
> +vn_reference_lookup_2 (ao_ref *op, tree vuse, void *data_)
> {
> vn_walk_cb_data *data = (vn_walk_cb_data *)data_;
> vn_reference_t vr = data->vr;
> @@ -2307,6 +2310,36 @@ vn_reference_lookup_2 (ao_ref *op ATTRIBUTE_UNUSED,
> tree vuse, void *data_)
> return *slot;
> }
>
> + if (SSA_NAME_IS_DEFAULT_DEF (vuse))
> + {
> + HOST_WIDE_INT offset, size;
> + tree v = NULL_TREE;
> + if (op->base && TREE_CODE (op->base) == PARM_DECL
> + && op->offset.is_constant (&offset)
> + && op->size.is_constant (&size))
you probably also want to check
op->max_size_known_p ()
&& known_eq (op->size, op->max_size)
I see data->partial_defs.is_empty () is already checked in this
function, but we won't currently ever call vn_reference_lookup_3
for default defs.
That said, ideally we'd handle also partial defs, but we can
start without.
> + v = ipcp_get_aggregate_const (op->base, false, offset, size);
> + else if (op->ref)
> + {
> + HOST_WIDE_INT offset, size;
> + bool reverse;
> + tree base = get_ref_base_and_extent_hwi (op->ref, &offset,
> + &size, &reverse);
> + if (base && TREE_CODE (base) == PARM_DECL)
In which case do you arrive here but op->base is not set above?
Maybe you need to use ao_ref_base (op->base) since op->base is
filled lazily from op->ref.
> + v = ipcp_get_aggregate_const (base, false, offset, size);
> + else if (base
> + && TREE_CODE (base) == MEM_REF
> + && integer_zerop (TREE_OPERAND (base, 1))
> + && TREE_CODE (TREE_OPERAND (base, 0)) == SSA_NAME
> + && SSA_NAME_IS_DEFAULT_DEF (TREE_OPERAND (base, 0))
> + && (TREE_CODE (SSA_NAME_VAR (TREE_OPERAND (base, 0)))
> + == PARM_DECL))
This code should also be in the op->base part.
I'd prefer if you pass DECL_BY_REFERENCE rather than second-guessing it
(or assert you guessed right).
> + v = ipcp_get_aggregate_const (SSA_NAME_VAR (TREE_OPERAND (base, 0)),
> + true, offset, size);
> + }
> + if (v)
> + return data->finish (vr->set, vr->base_set, v);
> + }
> +
> return NULL;
> }
>
>
--
Richard Biener <rguent...@suse.de>
SUSE Software Solutions Germany GmbH, Maxfeldstrasse 5, 90409 Nuernberg,
Germany; GF: Ivo Totev; HRB 36809 (AG Nuernberg)
