On Sun, 15 Nov 2020, Jan Hubicka wrote:
> Hi,
> one of common cases why we lose track on SSA name in modref propagation
> is the situation where name is passed to funtion call and we then thus
> continue by propagating through return value.
>
> This patch adds simple logic to track arguments that does not escape to
> return value. On cc1plus the improvement in PTA disambiguation is about
> 1.8% that is not too great, but it is easy enough to discover and often
> simplifies the propagation. I suppose this can be also useful for
> tree-ssa-structalias itself since it may also prevent args from escaping
> to return values.
>
> Bootstrapped/regtested x86_64-linux, OK?
OK. Can you amend the EAF_NOESCAPE comment to say "besides through
the return value"?
Thanks,
Richard.
> Honza
> * ipa-modref.c (dump_eaf_flags): Add EAF_NOT_RETURNED.
> (modref_lattice::init): Add EAF_NOT_RETURNED.
> (merge_call_lhs_flags): Do nothing for EAF_NOT_RETURNED
> args.
> (analyze_ssa_name_flags): Clear EAF_NOT_RETURNED on return;
> add EAF_NOT_RETURNED to call flags.
> (modref_merge_call_site_flags): Add EAF_NOT_RETURNED.
> * tree-core.h (EAF_NOT_RETURNED): New flags.
> diff --git a/gcc/ipa-modref.c b/gcc/ipa-modref.c
> index 7f673675d1d..155bf59fc53 100644
> --- a/gcc/ipa-modref.c
> +++ b/gcc/ipa-modref.c
> @@ -153,6 +153,8 @@ dump_eaf_flags (FILE *out, int flags, bool newline = true)
> fprintf (out, " noescape");
> if (flags & EAF_UNUSED)
> fprintf (out, " unused");
> + if (flags & EAF_NOT_RETURNED)
> + fprintf (out, " not_returned");
> if (newline)
> fprintf (out, "\n");
> }
> @@ -1361,7 +1363,8 @@ public:
> void
> modref_lattice::init ()
> {
> - flags = EAF_DIRECT | EAF_NOCLOBBER | EAF_NOESCAPE | EAF_UNUSED;
> + flags = EAF_DIRECT | EAF_NOCLOBBER | EAF_NOESCAPE | EAF_UNUSED
> + | EAF_NOT_RETURNED;
> open = true;
> known = false;
> }
> @@ -1531,6 +1534,9 @@ merge_call_lhs_flags (gcall *call, int arg, int index,
> bool deref,
> && (flags & ERF_RETURN_ARG_MASK) != arg)
> return;
>
> + if (gimple_call_arg_flags (call, arg) & EAF_NOT_RETURNED)
> + return;
> +
> /* If return value is SSA name determine its flags. */
> if (TREE_CODE (gimple_call_lhs (call)) == SSA_NAME)
> {
> @@ -1601,11 +1607,17 @@ analyze_ssa_name_flags (tree name,
> vec<modref_lattice> &lattice, int depth, bool
> print_gimple_stmt (dump_file, use_stmt, 0);
> }
>
> - /* Gimple return may load the return value. */
> + /* Gimple return may load the return value.
> + and clears EAF_NOT_RETURNED flag. */
> if (greturn *ret = dyn_cast <greturn *> (use_stmt))
> {
> if (memory_access_to (gimple_return_retval (ret), name))
> - lattice [index].merge_direct_load ();
> + {
> + lattice[index].merge_direct_load ();
> + lattice[index].merge (~EAF_NOT_RETURNED);
> + }
> + else if (gimple_return_retval (ret) == name)
> + lattice[index].merge (~EAF_NOT_RETURNED);
> }
> /* Account for LHS store, arg loads and flags from callee function. */
> else if (gcall *call = dyn_cast <gcall *> (use_stmt))
> @@ -1645,7 +1657,8 @@ analyze_ssa_name_flags (tree name, vec<modref_lattice>
> &lattice, int depth, bool
> {
> if (!(ecf_flags & (ECF_CONST | ECF_NOVOPS)))
> {
> - int call_flags = gimple_call_arg_flags (call, i);
> + int call_flags = gimple_call_arg_flags (call, i)
> + | EAF_NOT_RETURNED;
> if (ignore_stores)
> call_flags |= EAF_NOCLOBBER | EAF_NOESCAPE;
>
> @@ -1666,8 +1679,9 @@ analyze_ssa_name_flags (tree name, vec<modref_lattice>
> &lattice, int depth, bool
> lattice[index].merge_direct_load ();
> else
> {
> - int call_flags = deref_flags (gimple_call_arg_flags
> (call, i),
> - ignore_stores);
> + int call_flags = deref_flags
> + (gimple_call_arg_flags (call, i),
> + ignore_stores) | EAF_NOT_RETURNED;
> if (!record_ipa)
> lattice[index].merge (call_flags);
> if (record_ipa)
> @@ -3612,8 +3626,9 @@ modref_merge_call_site_flags (escape_summary *sum,
> flags |= EAF_NOESCAPE | EAF_NOCLOBBER;
> flags_lto |= EAF_NOESCAPE | EAF_NOCLOBBER;
> }
> - flags |= ee->min_flags;
> - flags_lto |= ee->min_flags;
> + /* Returning the value is already accounted to at local propagation.
> */
> + flags |= ee->min_flags | EAF_NOT_RETURNED;
> + flags_lto |= ee->min_flags | EAF_NOT_RETURNED;
> if (cur_summary && ee->parm_index < cur_summary->arg_flags.length ())
> {
> int f = cur_summary->arg_flags[ee->parm_index];
> diff --git a/gcc/tree-core.h b/gcc/tree-core.h
> index c9280a8d3b1..3e9455a553b 100644
> --- a/gcc/tree-core.h
> +++ b/gcc/tree-core.h
> @@ -110,6 +110,9 @@ struct die_struct;
> /* Nonzero if the argument is not used by the function. */
> #define EAF_UNUSED (1 << 3)
>
> +/* Nonzero if the argument does not escape to return value. */
> +#define EAF_NOT_RETURNED (1 << 4)
> +
> /* Call return flags. */
> /* Mask for the argument number that is returned. Lower two bits of
> the return flags, encodes argument slots zero to three. */
>
--
Richard Biener <rguent...@suse.de>
SUSE Software Solutions Germany GmbH, Maxfeldstrasse 5, 90409 Nuernberg,
Germany; GF: Felix Imend
