> Hi,
>
> On Fri, Nov 12 2021, Martin Jambor wrote:
> > Hi,
> >
> > using -fno-semantic-interposition has been reported by various people
> > to bring about considerable speed up at the cost of strict compliance
> > to the ELF symbol interposition rules See for example
> > https://fedoraproject.org/wiki/Changes/PythonNoSemanticInterpositionSpeedup
> >
> > As such I believe it should be implied by our -Ofast optimization
> > level, not only so that benchmarks that can benefit run faster, but
> > also so that people looking at -Ofast documentation for options that
> > could speed their programs find it.
> >
> > I have verified that with the following patch IPA-CP sees
> > flag_semantic_interposition set to zero at Ofast and that info and pdf
> > manual builds fine with the documentation change. I am bootstrapping
> > and testing it now in order to comply with submission criteria but I
> > don't think an Ofast change gets much tested.
> >
> > Assuming it passes, is the patch OK? (If it is, I will also add a note
> > about it in the "Caveats" section in gcc-12/changes.html of wwwdocs
> > after I commit the patch.)
> >
>
> Unfortunately, I was wrong, there are testcases which use the optimize
> attribute to switch a function to Ofast and those ICE because
> -fsemantic-interposition is not an optimization flag and only
> optimization flags can change in an optimize attribute (AFAIK, I only
> had a quick glance at the results).
>
> I am not sure what is the right way to tackle this, whether to set the
> flag at Ofast in some nonstandard way or make the flag an optimization
> flag - probably affecting function definitions, having it affect
> call-sites seems too fine-grained. I will try to discuss this on IRC on
> Monday (and hope such change is still doable early stage3).
>
> Sorry for posting this a bit prematurely,
Hi,
This patch turns flag_semantic_interposition to optimization option so
it can be enabled with per-function granuality. This is done by adding
the flag among visibility flags into the symbol table. This fixes the
behaviour on the testcase I added to testsuite.
There are bugs where get_availability misbehaves on partitioned program.
We can also use the new flag to fix those, but I will do that
incrementally.
The -Ofast change should be safe now.
Bootstrapped/regtested x86_64-linux, comitted.
gcc/ChangeLog:
2021-11-18 Jan Hubicka <hubi...@ucw.cz>
* cgraph.c (cgraph_node::get_availability): Update call of
decl_replaceable_p.
(cgraph_node::verify_node): Verify that semantic_interposition flag
is set correclty.
* cgraph.h: (symtab_node): Add semantic_interposition flag.
* cgraphclones.c (set_new_clone_decl_and_node_flags): Clear
semantic_interposition flag.
* cgraphunit.c (cgraph_node::finalize_function): Set
semantic_interposition flag.
(cgraph_node::add_new_function): Likewise.
(varpool_node::finalize_decl): Likewise.
(cgraph_node::create_wrapper): Likewise.
* common.opt (fsemantic-interposition): Turn to optimization node.
* lto-cgraph.c (lto_output_node): Stream semantic_interposition.
(lto_output_varpool_node): Likewise.
(input_overwrite_node): Likewise.
(input_varpool_node): Likewise.
* symtab.c (symtab_node::dump_base):
* varasm.c (decl_replaceable_p): Add semantic_interposition_p
parameter.
* varasm.h (decl_replaceable_p): Update declaration.
* varpool.c (varpool_node::ctor_useable_for_folding_p):
Use semantic_interposition flag.
(varpool_node::get_availability): Likewise.
(varpool_node::create_alias): Copy semantic_interposition flag.
gcc/cp/ChangeLog:
2021-11-18 Jan Hubicka <hubi...@ucw.cz>
* decl.c (finish_function): Update use of decl_replaceable_p.
gcc/lto/ChangeLog:
2021-11-18 Jan Hubicka <hubi...@ucw.cz>
* lto-partition.c (promote_symbol): Clear semantic_interposition flag.
gcc/testsuite/ChangeLog:
2021-11-18 Jan Hubicka <hubi...@ucw.cz>
* gcc.dg/lto/semantic-interposition-1_0.c: New test.
* gcc.dg/lto/semantic-interposition-1_1.c: New test.
diff --git a/gcc/cgraph.c b/gcc/cgraph.c
index 466b66d5ba5..8e7c12642ad 100644
--- a/gcc/cgraph.c
+++ b/gcc/cgraph.c
@@ -2390,7 +2390,8 @@ cgraph_node::get_availability (symtab_node *ref)
to code cp_cannot_inline_tree_fn and probably shall be shared and
the inlinability hooks completely eliminated). */
- else if (decl_replaceable_p (decl) && !DECL_EXTERNAL (decl))
+ else if (decl_replaceable_p (decl, semantic_interposition)
+ && !DECL_EXTERNAL (decl))
avail = AVAIL_INTERPOSABLE;
else avail = AVAIL_AVAILABLE;
@@ -3486,6 +3487,13 @@ cgraph_node::verify_node (void)
"returns a pointer");
error_found = true;
}
+ if (definition && externally_visible
+ && semantic_interposition
+ != opt_for_fn (decl, flag_semantic_interposition))
+ {
+ error ("semantic interposition mismatch");
+ error_found = true;
+ }
for (e = indirect_calls; e; e = e->next_callee)
{
if (e->aux)
diff --git a/gcc/cgraph.h b/gcc/cgraph.h
index e42e305cdb6..dafdfd289a0 100644
--- a/gcc/cgraph.h
+++ b/gcc/cgraph.h
@@ -117,6 +117,7 @@ public:
refuse_visibility_changes (false), externally_visible (false),
no_reorder (false), force_output (false), forced_by_abi (false),
unique_name (false), implicit_section (false), body_removed (false),
+ semantic_interposition (flag_semantic_interposition),
used_from_other_partition (false), in_other_partition (false),
address_taken (false), in_init_priority_hash (false),
need_lto_streaming (false), offloadable (false), ifunc_resolver (false),
@@ -557,6 +558,8 @@ public:
/* True when body and other characteristics have been removed by
symtab_remove_unreachable_nodes. */
unsigned body_removed : 1;
+ /* True when symbol should comply to -fsemantic-interposition flag. */
+ unsigned semantic_interposition : 1;
/*** WHOPR Partitioning flags.
These flags are used at ltrans stage when only part of the callgraph is
diff --git a/gcc/cgraphclones.c b/gcc/cgraphclones.c
index ae91dccd31d..c997b82f3e1 100644
--- a/gcc/cgraphclones.c
+++ b/gcc/cgraphclones.c
@@ -172,6 +172,7 @@ set_new_clone_decl_and_node_flags (cgraph_node *new_node)
new_node->externally_visible = 0;
new_node->local = 1;
new_node->lowered = true;
+ new_node->semantic_interposition = 0;
}
/* Duplicate thunk THUNK if necessary but make it to refer to NODE.
diff --git a/gcc/cgraphunit.c b/gcc/cgraphunit.c
index 55cb0347149..1e58ffd65e8 100644
--- a/gcc/cgraphunit.c
+++ b/gcc/cgraphunit.c
@@ -452,6 +452,7 @@ cgraph_node::finalize_function (tree decl, bool no_collect)
node->definition = true;
notice_global_symbol (decl);
node->lowered = DECL_STRUCT_FUNCTION (decl)->cfg != NULL;
+ node->semantic_interposition = opt_for_fn (decl,
flag_semantic_interposition);
if (!flag_toplevel_reorder)
node->no_reorder = true;
@@ -554,6 +555,8 @@ cgraph_node::add_new_function (tree fndecl, bool lowered)
node = cgraph_node::get_create (fndecl);
node->local = false;
node->definition = true;
+ node->semantic_interposition = opt_for_fn (fndecl,
+ flag_semantic_interposition);
node->force_output = true;
if (TREE_PUBLIC (fndecl))
node->externally_visible = true;
@@ -581,6 +584,8 @@ cgraph_node::add_new_function (tree fndecl, bool lowered)
if (lowered)
node->lowered = true;
node->definition = true;
+ node->semantic_interposition = opt_for_fn (fndecl,
+ flag_semantic_interposition);
node->analyze ();
push_cfun (DECL_STRUCT_FUNCTION (fndecl));
gimple_register_cfg_hooks ();
@@ -954,6 +959,7 @@ varpool_node::finalize_decl (tree decl)
/* Set definition first before calling notice_global_symbol so that
it is available to notice_global_symbol. */
node->definition = true;
+ node->semantic_interposition = flag_semantic_interposition;
notice_global_symbol (decl);
if (!flag_toplevel_reorder)
node->no_reorder = true;
@@ -2576,6 +2582,7 @@ cgraph_node::create_wrapper (cgraph_node *target)
/* Turn alias into thunk and expand it into GIMPLE representation. */
definition = true;
+ semantic_interposition = opt_for_fn (decl, flag_semantic_interposition);
/* Create empty thunk, but be sure we did not keep former thunk around.
In that case we would need to preserve the info. */
diff --git a/gcc/common.opt b/gcc/common.opt
index de9b848eda5..db6010e4e20 100644
--- a/gcc/common.opt
+++ b/gcc/common.opt
@@ -2539,7 +2539,7 @@ Common Var(flag_sel_sched_reschedule_pipelined) Init(0)
Optimization
Reschedule pipelined regions without pipelining.
fsemantic-interposition
-Common Var(flag_semantic_interposition) Init(1)
+Common Var(flag_semantic_interposition) Init(1) Optimization
Allow interposing function (or variables) by ones with different semantics (or
initializer) respectively by dynamic linker.
; sched_stalled_insns means that insns can be moved prematurely from the queue
diff --git a/gcc/cp/decl.c b/gcc/cp/decl.c
index 2ddf0e4a524..9f68d1a5590 100644
--- a/gcc/cp/decl.c
+++ b/gcc/cp/decl.c
@@ -17609,7 +17609,8 @@ finish_function (bool inline_p)
if (!processing_template_decl
&& !cp_function_chain->can_throw
&& !flag_non_call_exceptions
- && !decl_replaceable_p (fndecl))
+ && !decl_replaceable_p (fndecl,
+ opt_for_fn (fndecl, flag_semantic_interposition)))
TREE_NOTHROW (fndecl) = 1;
/* This must come after expand_function_end because cleanups might
diff --git a/gcc/lto-cgraph.c b/gcc/lto-cgraph.c
index 7c3e276a8ea..ef3c371c98f 100644
--- a/gcc/lto-cgraph.c
+++ b/gcc/lto-cgraph.c
@@ -516,6 +516,7 @@ lto_output_node (struct lto_simple_output_block *ob, struct
cgraph_node *node,
bp_pack_value (&bp, node->forced_by_abi, 1);
bp_pack_value (&bp, node->unique_name, 1);
bp_pack_value (&bp, node->body_removed, 1);
+ bp_pack_value (&bp, node->semantic_interposition, 1);
bp_pack_value (&bp, node->implicit_section, 1);
bp_pack_value (&bp, node->address_taken, 1);
bp_pack_value (&bp, tag == LTO_symtab_analyzed_node
@@ -604,6 +605,7 @@ lto_output_varpool_node (struct lto_simple_output_block
*ob, varpool_node *node,
node->body_removed
|| (!encode_initializer_p && !node->alias && node->definition),
1);
+ bp_pack_value (&bp, node->semantic_interposition, 1);
bp_pack_value (&bp, node->implicit_section, 1);
bp_pack_value (&bp, node->writeonly, 1);
bp_pack_value (&bp, node->definition && (encode_initializer_p ||
node->alias),
@@ -1167,6 +1169,7 @@ input_overwrite_node (struct lto_file_decl_data
*file_data,
node->forced_by_abi = bp_unpack_value (bp, 1);
node->unique_name = bp_unpack_value (bp, 1);
node->body_removed = bp_unpack_value (bp, 1);
+ node->semantic_interposition = bp_unpack_value (bp, 1);
node->implicit_section = bp_unpack_value (bp, 1);
node->address_taken = bp_unpack_value (bp, 1);
node->used_from_other_partition = bp_unpack_value (bp, 1);
@@ -1373,6 +1376,7 @@ input_varpool_node (struct lto_file_decl_data *file_data,
node->forced_by_abi = bp_unpack_value (&bp, 1);
node->unique_name = bp_unpack_value (&bp, 1);
node->body_removed = bp_unpack_value (&bp, 1);
+ node->semantic_interposition = bp_unpack_value (&bp, 1);
node->implicit_section = bp_unpack_value (&bp, 1);
node->writeonly = bp_unpack_value (&bp, 1);
node->definition = bp_unpack_value (&bp, 1);
diff --git a/gcc/lto/lto-partition.c b/gcc/lto/lto-partition.c
index bee40218159..6d20555073e 100644
--- a/gcc/lto/lto-partition.c
+++ b/gcc/lto/lto-partition.c
@@ -1001,6 +1001,7 @@ promote_symbol (symtab_node *node)
so it is prevailing. This is important to keep binds_to_current_def_p
to work across partitions. */
node->resolution = LDPR_PREVAILING_DEF_IRONLY;
+ node->semantic_interposition = false;
DECL_VISIBILITY (node->decl) = VISIBILITY_HIDDEN;
DECL_VISIBILITY_SPECIFIED (node->decl) = true;
if (dump_file)
diff --git a/gcc/symtab.c b/gcc/symtab.c
index c7ea8ecef74..94b4e47f749 100644
--- a/gcc/symtab.c
+++ b/gcc/symtab.c
@@ -929,6 +929,8 @@ symtab_node::dump_base (FILE *f)
fprintf (f, " forced_by_abi");
if (externally_visible)
fprintf (f, " externally_visible");
+ if (semantic_interposition)
+ fprintf (f, " semantic_interposition");
if (no_reorder)
fprintf (f, " no_reorder");
if (resolution != LDPR_UNKNOWN)
diff --git a/gcc/testsuite/gcc.dg/lto/semantic-interposition-1_0.c
b/gcc/testsuite/gcc.dg/lto/semantic-interposition-1_0.c
new file mode 100644
index 00000000000..db842749008
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/lto/semantic-interposition-1_0.c
@@ -0,0 +1,13 @@
+/* { dg-lto-do link } */
+/* { dg-require-effective-target shared } */
+/* { dg-extra-ld-options { -shared } } */
+/* { dg-lto-options {{-O2 -flto -fpic -fdump-ipa-inline-details --shared}} }
*/
+extern int ret1();
+
+int
+test()
+{
+ return ret1();
+}
+/* { dg-final { scan-wpa-ipa-dump "Inlined 1 calls" "inline" } } */
+
diff --git a/gcc/testsuite/gcc.dg/lto/semantic-interposition-1_1.c
b/gcc/testsuite/gcc.dg/lto/semantic-interposition-1_1.c
new file mode 100644
index 00000000000..9a741773002
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/lto/semantic-interposition-1_1.c
@@ -0,0 +1,5 @@
+/* { dg-options "-O2 -flto -fpic -fno-semantic-interposition" } */
+int ret1()
+{
+ return 1;
+}
diff --git a/gcc/varasm.c b/gcc/varasm.c
index 09316c62050..8c7aba2db61 100644
--- a/gcc/varasm.c
+++ b/gcc/varasm.c
@@ -7625,6 +7625,8 @@ decl_binds_to_current_def_p (const_tree decl)
at link-time with an entirely different definition, provided that the
replacement has the same type. For example, functions declared
with __attribute__((weak)) on most systems are replaceable.
+ If SEMANTIC_INTERPOSITION_P is false allow interposition only on
+ symbols explicitly declared weak.
COMDAT functions are not replaceable, since all definitions of the
function must be equivalent. It is important that COMDAT functions
@@ -7632,12 +7634,12 @@ decl_binds_to_current_def_p (const_tree decl)
instantiations is not penalized. */
bool
-decl_replaceable_p (tree decl)
+decl_replaceable_p (tree decl, bool semantic_interposition_p)
{
gcc_assert (DECL_P (decl));
if (!TREE_PUBLIC (decl) || DECL_COMDAT (decl))
return false;
- if (!flag_semantic_interposition
+ if (!semantic_interposition_p
&& !DECL_WEAK (decl))
return false;
return !decl_binds_to_current_def_p (decl);
diff --git a/gcc/varasm.h b/gcc/varasm.h
index 442ca6a380a..4ab9dc51838 100644
--- a/gcc/varasm.h
+++ b/gcc/varasm.h
@@ -38,7 +38,7 @@ extern void mark_decl_referenced (tree);
extern void notice_global_symbol (tree);
extern void set_user_assembler_name (tree, const char *);
extern void process_pending_assemble_externals (void);
-extern bool decl_replaceable_p (tree);
+extern bool decl_replaceable_p (tree, bool);
extern bool decl_binds_to_current_def_p (const_tree);
extern enum tls_model decl_default_tls_model (const_tree);
diff --git a/gcc/varpool.c b/gcc/varpool.c
index 4830df5c320..fd0d53b9eb6 100644
--- a/gcc/varpool.c
+++ b/gcc/varpool.c
@@ -372,7 +372,8 @@ varpool_node::ctor_useable_for_folding_p (void)
*/
if ((!DECL_INITIAL (real_node->decl)
|| (DECL_WEAK (decl) && !DECL_COMDAT (decl)))
- && (DECL_EXTERNAL (decl) || decl_replaceable_p (decl)))
+ && ((DECL_EXTERNAL (decl) && !in_other_partition)
+ || decl_replaceable_p (decl, semantic_interposition)))
return false;
/* Variables declared `const' with an initializer are considered
@@ -511,8 +512,8 @@ varpool_node::get_availability (symtab_node *ref)
/* If the variable can be overwritten, return OVERWRITABLE. Takes
care of at least one notable extension - the COMDAT variables
used to share template instantiations in C++. */
- if (decl_replaceable_p (decl)
- || DECL_EXTERNAL (decl))
+ if (decl_replaceable_p (decl, semantic_interposition)
+ || (DECL_EXTERNAL (decl) && !in_other_partition))
return AVAIL_INTERPOSABLE;
return AVAIL_AVAILABLE;
}
@@ -779,6 +780,7 @@ varpool_node::create_alias (tree alias, tree decl)
alias_node = varpool_node::get_create (alias);
alias_node->alias = true;
alias_node->definition = true;
+ alias_node->semantic_interposition = flag_semantic_interposition;
alias_node->alias_target = decl;
if (lookup_attribute ("weakref", DECL_ATTRIBUTES (alias)) != NULL)
alias_node->weakref = alias_node->transparent_alias = true;
