analyzer: fix state explosions due to SCC bug

Debugging the state explosion of the very large switch statement in
gcc.dg/analyzer/pr96653.c showed that the worklist was failing to
order the exploded nodes correctly; the in-edges at the join point
after the switch were not getting processed together, but were instead
being rocessed in smaller batches, bloating the exploded graph until the
per-point limit was reached.

The root cause turned out to be a bug in creating the strongly-connected
components for the supergraph: the code was considering interprocedural
edges as well as intraprocedural edges, leading to unpredictable
misorderings of the SCC and worklist, leading to bloating of the
exploded graph.

This patch fixes the SCC creation so it only considers intraprocedural
edges within the supergraph.  It also tweaks worklist::key_t::cmp to
give higher precedence to call_string over differences within a
supernode, since enodes with different call_strings can't be merges.
In practise, none of my test cases were affected by this latter change,
though it seems to be the right thing to do.

With this patch, the very large switch statement in
gcc.dg/analyzer/pr96653.c is handled in a single call to
exploded_graph::maybe_process_run_of_before_supernode_enodes:
   merged 358 in-enodes into 2 out-enode(s) at SN: 402
and that testcase no longer hits the per-program-point limits.

gcc/analyzer/ChangeLog:
	* engine.cc (strongly_connected_components::strong_connect): Only
	consider intraprocedural edges when creating SCCs.
	(worklist::key_t::cmp): Add comment.  Treat call_string
	differences as more important than differences of program_point
	within a supernode.

gcc/testsuite/ChangeLog:
	PR analyzer/96653
	* gcc.dg/analyzer/loop-0-up-to-n-by-1-with-iter-obj.c: Update
	expected number of exploded nodes.
	* gcc.dg/analyzer/malloc-vs-local-1a.c: Update expected number
	of exploded nodes.
	* gcc.dg/analyzer/pr96653.c: Remove -Wno-analyzer-too-complex.

diff --git a/gcc/analyzer/engine.cc b/gcc/analyzer/engine.cc
index 637a990..d03e23a 100644 (file)
--- a/gcc/analyzer/engine.cc
+++ b/gcc/analyzer/engine.cc
@@ -1615,6 +1615,9 @@ strongly_connected_components::strong_connect (unsigned index)
   superedge *sedge;
   FOR_EACH_VEC_ELT (v_snode->m_succs, i, sedge)
     {
+      if (sedge->get_kind () != SUPEREDGE_CFG_EDGE
+         && sedge->get_kind () != SUPEREDGE_INTRAPROCEDURAL_CALL)
+       continue;
       supernode *w_snode = sedge->m_dest;
       per_node_data *w = &m_per_node[w_snode->m_index];
       if (w->m_index == -1)
@@ -1690,7 +1693,14 @@ worklist::add_node (exploded_node *enode)
 /* Comparator for implementing worklist::key_t comparison operators.
    Return negative if KA is before KB
    Return positive if KA is after KB
-   Return 0 if they are equal.  */
+   Return 0 if they are equal.
+
+   The ordering of the worklist is critical for performance and for
+   avoiding node explosions.  Ideally we want all enodes at a CFG join-point
+   with the same callstring to be sorted next to each other in the worklist
+   so that a run of consecutive enodes can be merged and processed "in bulk"
+   rather than individually or pairwise, minimizing the number of new enodes
+   created.  */
 
 int
 worklist::key_t::cmp (const worklist::key_t &ka, const worklist::key_t &kb)
@@ -1742,6 +1752,11 @@ worklist::key_t::cmp (const worklist::key_t &ka, const worklist::key_t &kb)
 
   gcc_assert (snode_a == snode_b);
 
+  /* The points might vary by callstring; try sorting by callstring.  */
+  int cs_cmp = call_string::cmp (call_string_a, call_string_b);
+  if (cs_cmp)
+    return cs_cmp;
+
   /* Order within supernode via program point.  */
   int within_snode_cmp
     = function_point::cmp_within_supernode (point_a.get_function_point (),
@@ -1749,11 +1764,6 @@ worklist::key_t::cmp (const worklist::key_t &ka, const worklist::key_t &kb)
   if (within_snode_cmp)
     return within_snode_cmp;
 
-  /* The points might vary by callstring; try sorting by callstring.  */
-  int cs_cmp = call_string::cmp (call_string_a, call_string_b);
-  if (cs_cmp)
-    return cs_cmp;
-
   /* Otherwise, we ought to have the same program_point.  */
   gcc_assert (point_a == point_b);
 

diff --git a/gcc/testsuite/gcc.dg/analyzer/loop-0-up-to-n-by-1-with-iter-obj.c b/gcc/testsuite/gcc.dg/analyzer/loop-0-up-to-n-by-1-with-iter-obj.c
index 0172c9b..2b03527 100644 (file)
--- a/gcc/testsuite/gcc.dg/analyzer/loop-0-up-to-n-by-1-with-iter-obj.c
+++ b/gcc/testsuite/gcc.dg/analyzer/loop-0-up-to-n-by-1-with-iter-obj.c
@@ -69,5 +69,6 @@ void test(int n)
 
   free (it);
 
-  __analyzer_dump_exploded_nodes (0); /* { dg-warning "1 processed enode" } */
+  __analyzer_dump_exploded_nodes (0); /* { dg-warning "2 processed enodes" } */
+  // TODO: why 2 enodes here, rather than 1
 }

diff --git a/gcc/testsuite/gcc.dg/analyzer/malloc-vs-local-1a.c b/gcc/testsuite/gcc.dg/analyzer/malloc-vs-local-1a.c
index 4e70694..bf77862 100644 (file)
--- a/gcc/testsuite/gcc.dg/analyzer/malloc-vs-local-1a.c
+++ b/gcc/testsuite/gcc.dg/analyzer/malloc-vs-local-1a.c
@@ -48,10 +48,10 @@ int test_repeated_predicate_1 (int n)
 
   result = do_stuff (ptr, n);
 
-  __analyzer_dump_exploded_nodes (0); /* { dg-warning "5 processed enodes" } */
-  // FIXME: why 5 here?
-  __analyzer_dump_exploded_nodes (0); /* { dg-warning "5 processed enodes" } */
-  // FIXME: why 5 here?
+  __analyzer_dump_exploded_nodes (0); /* { dg-warning "2 processed enodes" } */
+
+  __analyzer_dump_exploded_nodes (0); /* { dg-warning "2 processed enodes" } */
+
 
   if (n > 10)
     free (ptr); /* { dg-bogus "not on the heap" } */
@@ -105,8 +105,8 @@ int test_explicit_flag (int n)
 
   result = do_stuff (ptr, n);
 
-  __analyzer_dump_exploded_nodes (0); /* { dg-warning "5 processed enodes" } */
-  // FIXME: why 5 here?
+  __analyzer_dump_exploded_nodes (0); /* { dg-warning "2 processed enodes" } */
+
 
   if (need_to_free)
     free (ptr); /* { dg-bogus "not on the heap" } */
@@ -131,8 +131,8 @@ int test_pointer_comparison (int n)
 
   result = do_stuff (ptr, n);
 
-  __analyzer_dump_exploded_nodes (0); /* { dg-warning "5 processed enodes" } */
-  // FIXME: why 5 here?
+  __analyzer_dump_exploded_nodes (0); /* { dg-warning "2 processed enodes" } */
+
 
   if (ptr != buf)
     free (ptr); /* { dg-bogus "not on the heap" } */
@@ -169,8 +169,8 @@ int test_initial_flag (int n)
 
   result = do_stuff (ptr, n);
 
-  __analyzer_dump_exploded_nodes (0); /* { dg-warning "6 processed enodes" } */
-  // FIXME: why 6 here?
+  __analyzer_dump_exploded_nodes (0); /* { dg-warning "3 processed enodes" } */
+  // FIXME: why 3 here?
 
   if (n > 10)
     free (ptr); /* { dg-bogus "not on the heap" } */

diff --git a/gcc/testsuite/gcc.dg/analyzer/pr96653.c b/gcc/testsuite/gcc.dg/analyzer/pr96653.c
index 494c531..e5e387c 100644 (file)
--- a/gcc/testsuite/gcc.dg/analyzer/pr96653.c
+++ b/gcc/testsuite/gcc.dg/analyzer/pr96653.c
@@ -1,8 +1,7 @@
 /* Examples of switch statements with many cases (with default values).
    Adapted from Linux 5.9-rc1:drivers/media/v4l2-core/v4l2-ctrls.c.  */
 
-/* { dg-additional-options "-O1 -Wno-analyzer-too-complex" } */
-// TODO: remove need for -Wno-analyzer-too-complex
+/* { dg-additional-options "-O1" } */
 
 typedef unsigned int u32;
 typedef long long s64;