Re: Fix ICE in estimate_bb_frequencies

[Markus Trippelsdorf]

On 2017.07.18 at 09:54 +0200, Jan Hubicka wrote:
> Hi,
> this patch fixes ICE in estimate_bb_frequencies which triggers because we 
> forget
> to compute probability for blocks whose count is earlier statically 
> determined to be
> 0.
> 
> Bootstrapped/regtested x86_64-linux, will commit it shortly.

It also fixes both testcases from PR81318.

However the following testcase still ICEs:

trippels@gcc2-power8 linux % cat main.i
int a;
extern void fn4();
__attribute__((__cold__)) void fn1();
void fn2() { fn1(); }
void fn3() {
  fn2();
  if (a)
fn4();
}

trippels@gcc2-power8 linux % gcc -O2 -c main.i
during GIMPLE pass: profile_estimate
main.i: In function ‘fn3’:
main.i:9:1: internal compiler error: in to_reg_br_prob_base, at 
profile-count.h:189

-- 
Markus

Fix ICE in estimate_bb_frequencies

[Jan Hubicka]

Hi,
this patch fixes ICE in estimate_bb_frequencies which triggers because we forget
to compute probability for blocks whose count is earlier statically determined 
to be
0.

Bootstrapped/regtested x86_64-linux, will commit it shortly.

Honza

PR middle-end/81462
* predict.c (set_even_probabilities): Cleanup; do not affect
probabilities that are already known.
(combine_predictions_for_bb): Call even when count is set.

* g++.dg/torture/pr81462.C: New testcase.

Index: predict.c
===
--- predict.c   (revision 250295)
+++ predict.c   (working copy)
@@ -817,16 +817,25 @@ static void
 set_even_probabilities (basic_block bb,
hash_set *unlikely_edges = NULL)
 {
-  unsigned nedges = 0;
+  unsigned nedges = 0, unlikely_count = 0;
   edge e = NULL;
   edge_iterator ei;
+  profile_probability all = profile_probability::always ();
 
   FOR_EACH_EDGE (e, ei, bb->succs)
-if (!unlikely_executed_edge_p (e))
-  nedges ++;
+if (e->probability.initialized_p ())
+  all -= e->probability;
+else if (!unlikely_executed_edge_p (e))
+  {
+nedges ++;
+if (unlikely_edges != NULL && unlikely_edges->contains (e))
+ {
+   all -= profile_probability::very_unlikely ();
+   unlikely_count++;
+ }
+  }
 
   /* Make the distribution even if all edges are unlikely.  */
-  unsigned unlikely_count = unlikely_edges ? unlikely_edges->elements () : 0;
   if (unlikely_count == nedges)
 {
   unlikely_edges = NULL;
@@ -836,13 +845,14 @@ set_even_probabilities (basic_block bb,
   unsigned c = nedges - unlikely_count;
 
   FOR_EACH_EDGE (e, ei, bb->succs)
-if (!unlikely_executed_edge_p (e))
+if (e->probability.initialized_p ())
+  ;
+else if (!unlikely_executed_edge_p (e))
   {
if (unlikely_edges != NULL && unlikely_edges->contains (e))
  e->probability = profile_probability::very_unlikely ();
else
- e->probability = profile_probability::guessed_always ()
-   .apply_scale (1, c);
+ e->probability = all.apply_scale (1, c).guessed ();
   }
 else
   e->probability = profile_probability::never ();
@@ -1151,7 +1161,7 @@ combine_predictions_for_bb (basic_block
  if (pred->ep_probability <= PROB_VERY_UNLIKELY)
unlikely_edges.add (pred->ep_edge);
 
-  if (!bb->count.initialized_p () && !dry_run)
+  if (!dry_run)
set_even_probabilities (bb, _edges);
   clear_bb_predictions (bb);
   if (dump_file)
Index: testsuite/g++.dg/torture/pr81462.C
===
--- testsuite/g++.dg/torture/pr81462.C  (revision 0)
+++ testsuite/g++.dg/torture/pr81462.C  (working copy)
@@ -0,0 +1,17 @@
+// { dg-do compile }
+// { dg-options "-O1 -fno-ipa-pure-const" }
+struct B {
+B* self;
+B() : self( this ) { self->f(); }
+virtual void f() = 0;
+};
+
+struct D : B
+{
+void f() {}
+};
+
+int main()
+{
+D d;
+}