Re: [PATCH] Do not allow to inline ifunc resolvers (PR ipa/81128).

[Martin Liška <mliska at suse dot cz>]

On 06/27/2017 04:57 PM, Jan Hubicka wrote:
>> Hello.
>>
>> Currently ifunc is interpreted as normal alias by IPA optimizations. That's problematic
>> as should not consider ifunc alias as candidate for inlining, or redirection.
>>
>> Patch can bootstrap on ppc64le-redhat-linux and survives regression tests.
>> And survives MVC tests on x86_64-linux-gnu.
>>
>> Ready to be installed?
> 
> Wasn't this supposed to go with arranging availability to be AVAIL_INTERPOSABLE
> (as the target will be interposed by linker to the corect target)

Should work, there's alternative patch:

diff --git a/gcc/c-family/c-attribs.c b/gcc/c-family/c-attribs.c
index 2b6845f2cbd..626ffa1cde7 100644
--- a/gcc/c-family/c-attribs.c
+++ b/gcc/c-family/c-attribs.c
@@ -1846,9 +1846,14 @@ handle_alias_ifunc_attribute (bool is_alias, tree *node, tree name, tree args,
        TREE_STATIC (decl) = 1;
 
       if (!is_alias)
-       /* ifuncs are also aliases, so set that attribute too.  */
-       DECL_ATTRIBUTES (decl)
-         = tree_cons (get_identifier ("alias"), args, DECL_ATTRIBUTES (decl));
+       {
+         /* ifuncs are also aliases, so set that attribute too.  */
+         DECL_ATTRIBUTES (decl)
+           = tree_cons (get_identifier ("alias"), args,
+                        DECL_ATTRIBUTES (decl));
+         DECL_ATTRIBUTES (decl) = tree_cons (get_identifier ("ifunc"),
+                                             NULL, DECL_ATTRIBUTES (decl));
+       }
     }
   else
     {
diff --git a/gcc/ipa-visibility.c b/gcc/ipa-visibility.c
index d5a3ae56c46..69e6e295d55 100644
--- a/gcc/ipa-visibility.c
+++ b/gcc/ipa-visibility.c
@@ -97,7 +97,8 @@ non_local_p (struct cgraph_node *node, void *data ATTRIBUTE_UNUSED)
           && !DECL_EXTERNAL (node->decl)
           && !node->externally_visible
           && !node->used_from_other_partition
-          && !node->in_other_partition);
+          && !node->in_other_partition
+          && !lookup_attribute ("ifunc", DECL_ATTRIBUTES (node->decl)));
 }
 
 /* Return true when function can be marked local.  */

It's questionable if local.local can be true for ifunc function? If can, one would need to
move check for ifunc aerly in:
/* Return function availability.  See cgraph.h for description of individual
   return values.  */
enum availability
cgraph_node::get_availability (symtab_node *ref)
{
  if (ref)
    {
      cgraph_node *cref = dyn_cast <cgraph_node *> (ref);
      if (cref)
	ref = cref->global.inlined_to;
    }
  enum availability avail;
  if (!analyzed)
    avail = AVAIL_NOT_AVAILABLE;
  else if (local.local)
    avail = AVAIL_LOCAL;
  else if (global.inlined_to)
    avail = AVAIL_AVAILABLE;
  else if (transparent_alias)
    ultimate_alias_target (&avail, ref);
  else if (lookup_attribute ("ifunc", DECL_ATTRIBUTES (decl)))
    avail = AVAIL_INTERPOSABLE;

...

What solution do you prefer Honza?

Thanks,
Martin

> 
> Honza
>> Martin
>>
>> gcc/ChangeLog:
>>
>> 2017-06-22  Martin Liska  <mliska@suse.cz>
>>
>> 	* ipa-inline.c (can_inline_edge_p): Return false for ifunc fns.
>> 	* ipa-visibility.c (can_replace_by_local_alias): Likewise.
>>
>> gcc/c-family/ChangeLog:
>>
>> 2017-06-22  Martin Liska  <mliska@suse.cz>
>>
>> 	* c-attribs.c (handle_alias_ifunc_attribute): Append ifunc alias
>> 	to a function declaration.
>>
>> gcc/testsuite/ChangeLog:
>>
>> 2017-06-22  Martin Liska  <mliska@suse.cz>
>>
>> 	* gcc.target/i386/pr81128.c: New test.
>> ---
>>  gcc/c-family/c-attribs.c                | 11 ++++--
>>  gcc/ipa-inline.c                        |  2 +
>>  gcc/ipa-visibility.c                    |  3 +-
>>  gcc/testsuite/gcc.target/i386/pr81128.c | 65 +++++++++++++++++++++++++++++++++
>>  4 files changed, 77 insertions(+), 4 deletions(-)
>>  create mode 100644 gcc/testsuite/gcc.target/i386/pr81128.c
>>
>>
> 
>> diff --git a/gcc/c-family/c-attribs.c b/gcc/c-family/c-attribs.c
>> index 2b6845f2cbd..626ffa1cde7 100644
>> --- a/gcc/c-family/c-attribs.c
>> +++ b/gcc/c-family/c-attribs.c
>> @@ -1846,9 +1846,14 @@ handle_alias_ifunc_attribute (bool is_alias, tree *node, tree name, tree args,
>>  	TREE_STATIC (decl) = 1;
>>  
>>        if (!is_alias)
>> -	/* ifuncs are also aliases, so set that attribute too.  */
>> -	DECL_ATTRIBUTES (decl)
>> -	  = tree_cons (get_identifier ("alias"), args, DECL_ATTRIBUTES (decl));
>> +	{
>> +	  /* ifuncs are also aliases, so set that attribute too.  */
>> +	  DECL_ATTRIBUTES (decl)
>> +	    = tree_cons (get_identifier ("alias"), args,
>> +			 DECL_ATTRIBUTES (decl));
>> +	  DECL_ATTRIBUTES (decl) = tree_cons (get_identifier ("ifunc"),
>> +					      NULL, DECL_ATTRIBUTES (decl));
>> +	}
>>      }
>>    else
>>      {
>> diff --git a/gcc/ipa-inline.c b/gcc/ipa-inline.c
>> index fb20d3723cc..588fa9c41e4 100644
>> --- a/gcc/ipa-inline.c
>> +++ b/gcc/ipa-inline.c
>> @@ -370,6 +370,8 @@ can_inline_edge_p (struct cgraph_edge *e, bool report,
>>        e->inline_failed = CIF_ATTRIBUTE_MISMATCH;
>>        inlinable = false;
>>      }
>> +  else if (lookup_attribute ("ifunc", DECL_ATTRIBUTES (e->callee->decl)))
>> +      inlinable = false;
>>    /* Check if caller growth allows the inlining.  */
>>    else if (!DECL_DISREGARD_INLINE_LIMITS (callee->decl)
>>  	   && !disregard_limits
>> diff --git a/gcc/ipa-visibility.c b/gcc/ipa-visibility.c
>> index d5a3ae56c46..79d05b41085 100644
>> --- a/gcc/ipa-visibility.c
>> +++ b/gcc/ipa-visibility.c
>> @@ -345,7 +345,8 @@ can_replace_by_local_alias (symtab_node *node)
>>    
>>    return (node->get_availability () > AVAIL_INTERPOSABLE
>>  	  && !decl_binds_to_current_def_p (node->decl)
>> -	  && !node->can_be_discarded_p ());
>> +	  && !node->can_be_discarded_p ()
>> +	  && !lookup_attribute ("ifunc", DECL_ATTRIBUTES (node->decl)));
>>  }
>>  
>>  /* Return true if we can replace reference to NODE by local alias
>> diff --git a/gcc/testsuite/gcc.target/i386/pr81128.c b/gcc/testsuite/gcc.target/i386/pr81128.c
>> new file mode 100644
>> index 00000000000..90a567ad690
>> --- /dev/null
>> +++ b/gcc/testsuite/gcc.target/i386/pr81128.c
>> @@ -0,0 +1,65 @@
>> +/* PR ipa/81128 */
>> +/* { dg-do run } */
>> +/* { dg-options "-O3" } */
>> +/* { dg-require-ifunc "" } */
>> +
>> +
>> +#include <stdio.h>
>> +#include <stdlib.h>
>> +#include <time.h>
>> +
>> +int resolver_fn = 0;
>> +int resolved_fn = 0;
>> +
>> +static inline void
>> +do_it_right_at_runtime_A ()
>> +{
>> +  resolved_fn++;
>> +}
>> +
>> +static inline void
>> +do_it_right_at_runtime_B ()
>> +{
>> +  resolved_fn++;
>> +}
>> +
>> +static inline void do_it_right_at_runtime (void);
>> +
>> +void do_it_right_at_runtime (void)
>> +  __attribute__ ((ifunc ("resolve_do_it_right_at_runtime")));
>> +
>> +static void (*resolve_do_it_right_at_runtime (void)) (void)
>> +{
>> +  srand (time (NULL));
>> +  int r = rand ();
>> +  resolver_fn++;
>> +
>> +  /* Use intermediate variable to get a warning for non-matching
>> +   * prototype. */
>> +  typeof(do_it_right_at_runtime) *func;
>> +  if (r & 1)
>> +    func = do_it_right_at_runtime_A;
>> +  else
>> +    func = do_it_right_at_runtime_B;
>> +
>> +  return (void *) func;
>> +}
>> +
>> +int
>> +main (void)
>> +{
>> +  const unsigned int ITERS = 10;
>> +
>> +  for (int i = ITERS; i > 0; i--)
>> +    {
>> +      do_it_right_at_runtime ();
>> +    }
>> +
>> +  if (resolver_fn != 1)
>> +    __builtin_abort ();
>> +
>> +  if (resolved_fn != 10)
>> +    __builtin_abort ();
>> +
>> +  return 0;
>> +}
>>
>