diff mbox series

[v2] ipa-utils: avoid uninitialized probabilities on ICF [PR111559]

Message ID 20231001192943.3473530-1-slyich@gmail.com
State Accepted
Headers
Series [v2] ipa-utils: avoid uninitialized probabilities on ICF [PR111559] |

Checks

Context Check Description
snail/gcc-patch-check success Github commit url

Commit Message

Sergei Trofimovich Oct. 1, 2023, 7:29 p.m. UTC 
  From: Sergei Trofimovich <siarheit@google.com>

r14-3459-g0c78240fd7d519 "Check that passes do not forget to define profile"
exposed check failures in cases when gcc produces uninitialized profile
probabilities. In case of PR/111559 uninitialized profile is generated
by edges executed 0 times reported by IPA profile:

    $ gcc -O2 -fprofile-generate pr111559.c -o b -fopt-info
    $ ./b
    $ gcc -O2 -fprofile-use -fprofile-correction pr111559.c -o b -fopt-info

    pr111559.c: In function 'rule1':
    pr111559.c:6:13: error: probability of edge 3->4 not initialized
        6 | static void rule1(void) { if (p) edge(); }
          |             ^~~~~
    during GIMPLE pass: fixup_cfg
    pr111559.c:6:13: internal compiler error: verify_flow_info failed

The change conservatively ignores updates with uninitialized values and
uses initially assigned probabilities (`always` probability in case of
the example).

	PR ipa/111283
	PR gcov-profile/111559

gcc/
	* ipa-utils.cc (ipa_merge_profiles): Avoid producing
	uninitialized probabilities when merging counters with zero
	denominators.

gcc/testsuite/
	* gcc.dg/tree-prof/pr111559.c: New test.
---
 gcc/ipa-utils.cc                          |  6 +++++-
 gcc/testsuite/gcc.dg/tree-prof/pr111559.c | 16 ++++++++++++++++
 2 files changed, 21 insertions(+), 1 deletion(-)
 create mode 100644 gcc/testsuite/gcc.dg/tree-prof/pr111559.c

Comments

Jan Hubicka Oct. 5, 2023, 11:52 a.m. UTC | #1 
> From: Sergei Trofimovich <siarheit@google.com>
> 
> r14-3459-g0c78240fd7d519 "Check that passes do not forget to define profile"
> exposed check failures in cases when gcc produces uninitialized profile
> probabilities. In case of PR/111559 uninitialized profile is generated
> by edges executed 0 times reported by IPA profile:
> 
>     $ gcc -O2 -fprofile-generate pr111559.c -o b -fopt-info
>     $ ./b
>     $ gcc -O2 -fprofile-use -fprofile-correction pr111559.c -o b -fopt-info
> 
>     pr111559.c: In function 'rule1':
>     pr111559.c:6:13: error: probability of edge 3->4 not initialized
>         6 | static void rule1(void) { if (p) edge(); }
>           |             ^~~~~
>     during GIMPLE pass: fixup_cfg
>     pr111559.c:6:13: internal compiler error: verify_flow_info failed
> 
> The change conservatively ignores updates with uninitialized values and
> uses initially assigned probabilities (`always` probability in case of
> the example).
> 
> 	PR ipa/111283
> 	PR gcov-profile/111559
> 
> gcc/
> 	* ipa-utils.cc (ipa_merge_profiles): Avoid producing
> 	uninitialized probabilities when merging counters with zero
> 	denominators.
> 
> gcc/testsuite/
> 	* gcc.dg/tree-prof/pr111559.c: New test.
> ---
>  gcc/ipa-utils.cc                          |  6 +++++-
>  gcc/testsuite/gcc.dg/tree-prof/pr111559.c | 16 ++++++++++++++++
>  2 files changed, 21 insertions(+), 1 deletion(-)
>  create mode 100644 gcc/testsuite/gcc.dg/tree-prof/pr111559.c
> 
> diff --git a/gcc/ipa-utils.cc b/gcc/ipa-utils.cc
> index 956c6294fd7..7c53ae9dd45 100644
> --- a/gcc/ipa-utils.cc
> +++ b/gcc/ipa-utils.cc
> @@ -651,13 +651,17 @@ ipa_merge_profiles (struct cgraph_node *dst,
>  		{
>  		  edge srce = EDGE_SUCC (srcbb, i);
>  		  edge dste = EDGE_SUCC (dstbb, i);
> -		  dste->probability = 
> +		  profile_probability merged =
>  		    dste->probability * dstbb->count.ipa ().probability_in
>  						 (dstbb->count.ipa ()
>  						  + srccount.ipa ())
>  		    + srce->probability * srcbb->count.ipa ().probability_in
>  						 (dstbb->count.ipa ()
>  						  + srccount.ipa ());
> +		  /* We produce uninitialized probabilities when
> +		     denominator is zero: https://gcc.gnu.org/PR111559.  */
> +		  if (merged.initialized_p ())
> +		    dste->probability = merged;

Thanks for the patch.
We usually avoid the uninitialized value here by simply checking that
parameter of probability_in satifies nonzero_p.  So I think it would be
more consistent doing it here to:

  profile_probability sum = dstbb->count.ipa () + srccount.ipa ()
  if (sum.nonzero_p ())
  {
     dste->probability = .....
  }

OK with this change.
Honza
>  		}
>  	      dstbb->count = dstbb->count.ipa () + srccount.ipa ();
>  	    }
> diff --git a/gcc/testsuite/gcc.dg/tree-prof/pr111559.c b/gcc/testsuite/gcc.dg/tree-prof/pr111559.c
> new file mode 100644
> index 00000000000..43202c6c888
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/tree-prof/pr111559.c
> @@ -0,0 +1,16 @@
> +/* { dg-options "-O2" } */
> +
> +__attribute__((noipa)) static void edge(void) {}
> +
> +int p = 0;
> +
> +__attribute__((noinline))
> +static void rule1(void) { if (p) edge(); }
> +
> +__attribute__((noinline))
> +static void rule1_same(void) { if (p) edge(); }
> +
> +__attribute__((noipa)) int main(void) {
> +    rule1();
> +    rule1_same();
> +}
> -- 
> 2.42.0
>
Sergei Trofimovich Oct. 5, 2023, 12:46 p.m. UTC | #2 
On Thu, Oct 05, 2023 at 01:52:30PM +0200, Jan Hubicka wrote:
> > From: Sergei Trofimovich <siarheit@google.com>
> > 
> > r14-3459-g0c78240fd7d519 "Check that passes do not forget to define profile"
> > exposed check failures in cases when gcc produces uninitialized profile
> > probabilities. In case of PR/111559 uninitialized profile is generated
> > by edges executed 0 times reported by IPA profile:
> > 
> >     $ gcc -O2 -fprofile-generate pr111559.c -o b -fopt-info
> >     $ ./b
> >     $ gcc -O2 -fprofile-use -fprofile-correction pr111559.c -o b -fopt-info
> > 
> >     pr111559.c: In function 'rule1':
> >     pr111559.c:6:13: error: probability of edge 3->4 not initialized
> >         6 | static void rule1(void) { if (p) edge(); }
> >           |             ^~~~~
> >     during GIMPLE pass: fixup_cfg
> >     pr111559.c:6:13: internal compiler error: verify_flow_info failed
> > 
> > The change conservatively ignores updates with uninitialized values and
> > uses initially assigned probabilities (`always` probability in case of
> > the example).
> > 
> > 	PR ipa/111283
> > 	PR gcov-profile/111559
> > 
> > gcc/
> > 	* ipa-utils.cc (ipa_merge_profiles): Avoid producing
> > 	uninitialized probabilities when merging counters with zero
> > 	denominators.
> > 
> > gcc/testsuite/
> > 	* gcc.dg/tree-prof/pr111559.c: New test.
> > ---
> >  gcc/ipa-utils.cc                          |  6 +++++-
> >  gcc/testsuite/gcc.dg/tree-prof/pr111559.c | 16 ++++++++++++++++
> >  2 files changed, 21 insertions(+), 1 deletion(-)
> >  create mode 100644 gcc/testsuite/gcc.dg/tree-prof/pr111559.c
> > 
> > diff --git a/gcc/ipa-utils.cc b/gcc/ipa-utils.cc
> > index 956c6294fd7..7c53ae9dd45 100644
> > --- a/gcc/ipa-utils.cc
> > +++ b/gcc/ipa-utils.cc
> > @@ -651,13 +651,17 @@ ipa_merge_profiles (struct cgraph_node *dst,
> >  		{
> >  		  edge srce = EDGE_SUCC (srcbb, i);
> >  		  edge dste = EDGE_SUCC (dstbb, i);
> > -		  dste->probability = 
> > +		  profile_probability merged =
> >  		    dste->probability * dstbb->count.ipa ().probability_in
> >  						 (dstbb->count.ipa ()
> >  						  + srccount.ipa ())
> >  		    + srce->probability * srcbb->count.ipa ().probability_in
> >  						 (dstbb->count.ipa ()
> >  						  + srccount.ipa ());
> > +		  /* We produce uninitialized probabilities when
> > +		     denominator is zero: https://gcc.gnu.org/PR111559.  */
> > +		  if (merged.initialized_p ())
> > +		    dste->probability = merged;
> 
> Thanks for the patch.
> We usually avoid the uninitialized value here by simply checking that
> parameter of probability_in satifies nonzero_p.  So I think it would be
> more consistent doing it here to:
> 
>   profile_probability sum = dstbb->count.ipa () + srccount.ipa ()
>   if (sum.nonzero_p ())
>   {
>      dste->probability = .....
>   }

Aha, sounds good! I had to do `s/profile_probability/profile_count` as
it's a denominator value for probability.

Attached v3 just in case.

> OK with this change.
> Honza
> >  		}
> >  	      dstbb->count = dstbb->count.ipa () + srccount.ipa ();
> >  	    }
> > diff --git a/gcc/testsuite/gcc.dg/tree-prof/pr111559.c b/gcc/testsuite/gcc.dg/tree-prof/pr111559.c
> > new file mode 100644
> > index 00000000000..43202c6c888
> > --- /dev/null
> > +++ b/gcc/testsuite/gcc.dg/tree-prof/pr111559.c
> > @@ -0,0 +1,16 @@
> > +/* { dg-options "-O2" } */
> > +
> > +__attribute__((noipa)) static void edge(void) {}
> > +
> > +int p = 0;
> > +
> > +__attribute__((noinline))
> > +static void rule1(void) { if (p) edge(); }
> > +
> > +__attribute__((noinline))
> > +static void rule1_same(void) { if (p) edge(); }
> > +
> > +__attribute__((noipa)) int main(void) {
> > +    rule1();
> > +    rule1_same();
> > +}
> > -- 
> > 2.42.0
> >
Jan Hubicka Oct. 5, 2023, 1:04 p.m. UTC | #3 
> diff --git a/gcc/ipa-utils.cc b/gcc/ipa-utils.cc
> index 956c6294fd7..1355ccac6f0 100644
> --- a/gcc/ipa-utils.cc
> +++ b/gcc/ipa-utils.cc
> @@ -651,13 +651,16 @@ ipa_merge_profiles (struct cgraph_node *dst,
>  		{
>  		  edge srce = EDGE_SUCC (srcbb, i);
>  		  edge dste = EDGE_SUCC (dstbb, i);
> -		  dste->probability = 
> -		    dste->probability * dstbb->count.ipa ().probability_in
> -						 (dstbb->count.ipa ()
> -						  + srccount.ipa ())
> -		    + srce->probability * srcbb->count.ipa ().probability_in
> -						 (dstbb->count.ipa ()
> -						  + srccount.ipa ());
> +		  profile_count sum =
> +		    dstbb->count.ipa () + srccount.ipa ();
> +		  if (sum.nonzero_p ())
> +		    dste->probability =
> +		      dste->probability * dstbb->count.ipa ().probability_in
> +						   (dstbb->count.ipa ()
> +						    + srccount.ipa ())
> +		      + srce->probability * srcbb->count.ipa ().probability_in
> +						   (dstbb->count.ipa ()
> +						    + srccount.ipa ());

looks good.  You can use probability_in (sum) 
in both of the places.

Honza
diff mbox series

Patch

diff --git a/gcc/ipa-utils.cc b/gcc/ipa-utils.cc
index 956c6294fd7..7c53ae9dd45 100644
--- a/gcc/ipa-utils.cc
+++ b/gcc/ipa-utils.cc
@@ -651,13 +651,17 @@  ipa_merge_profiles (struct cgraph_node *dst,
 		{
 		  edge srce = EDGE_SUCC (srcbb, i);
 		  edge dste = EDGE_SUCC (dstbb, i);
-		  dste->probability = 
+		  profile_probability merged =
 		    dste->probability * dstbb->count.ipa ().probability_in
 						 (dstbb->count.ipa ()
 						  + srccount.ipa ())
 		    + srce->probability * srcbb->count.ipa ().probability_in
 						 (dstbb->count.ipa ()
 						  + srccount.ipa ());
+		  /* We produce uninitialized probabilities when
+		     denominator is zero: https://gcc.gnu.org/PR111559.  */
+		  if (merged.initialized_p ())
+		    dste->probability = merged;
 		}
 	      dstbb->count = dstbb->count.ipa () + srccount.ipa ();
 	    }
diff --git a/gcc/testsuite/gcc.dg/tree-prof/pr111559.c b/gcc/testsuite/gcc.dg/tree-prof/pr111559.c
new file mode 100644
index 00000000000..43202c6c888
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-prof/pr111559.c
@@ -0,0 +1,16 @@ 
+/* { dg-options "-O2" } */
+
+__attribute__((noipa)) static void edge(void) {}
+
+int p = 0;
+
+__attribute__((noinline))
+static void rule1(void) { if (p) edge(); }
+
+__attribute__((noinline))
+static void rule1_same(void) { if (p) edge(); }
+
+__attribute__((noipa)) int main(void) {
+    rule1();
+    rule1_same();
+}