analyzer; reset sm-state for SSA names at def-stmts [PR93695,PR99044,PR99716]

Various false positives from -fanalyzer involve SSA names in loops,
where sm-state associated with an SSA name from one iteration is
erroneously reused in a subsequent iteration.

For example, PR analyzer/99716 describes a false
  "double 'fclose' of FILE 'fp'"
on:

  for (i = 0; i < 2; ++i) {
    FILE *fp = fopen ("/tmp/test", "w");
    fprintf (fp, "hello");
    fclose (fp);
  }

where the gimple of the loop body is:

  fp_7 = fopen ("/tmp/test", "w");
  __builtin_fwrite ("hello", 1, 5, fp_7);
  fclose (fp_7);
  i_10 = i_1 + 1;

where fp_7 transitions to "closed" at the fclose, but is not
reset at the subsequent fopen, leading to the false positive
when the fclose is re-reached.

The fix is to reset sm-state for svalues that involve an SSA name
at the SSA name's def-stmt, since the def-stmt effectively changes
the meaning of those related svalues.

gcc/analyzer/ChangeLog:
	PR analyzer/93695
	PR analyzer/99044
	PR analyzer/99716
	* engine.cc (exploded_node::on_stmt): Clear sm-state involving
	an SSA name at the def-stmt of that SSA name.
	* program-state.cc (sm_state_map::purge_state_involving): New.
	* program-state.h (sm_state_map::purge_state_involving): New decl.
	* region-model.cc (selftest::test_involves_p): New.
	(selftest::analyzer_region_model_cc_tests): Call it.
	* svalue.cc (class involvement_visitor): New class
	(svalue::involves_p): New.
	* svalue.h (svalue::involves_p): New decl.

gcc/testsuite/ChangeLog:
	PR analyzer/93695
	PR analyzer/99044
	PR analyzer/99716
	* gcc.dg/analyzer/attr-malloc-CVE-2019-19078-usb-leak.c: Remove
	xfail.
	* gcc.dg/analyzer/pr93695-1.c: New test.
	* gcc.dg/analyzer/pr99044-1.c: New test.
	* gcc.dg/analyzer/pr99044-2.c: New test.
	* gcc.dg/analyzer/pr99716-1.c: New test.
	* gcc.dg/analyzer/pr99716-2.c: New test.
	* gcc.dg/analyzer/pr99716-3.c: New test.

1 files changed, 34 insertions, 0 deletions

diff --git a/gcc/analyzer/svalue.cc b/gcc/analyzer/svalue.cc
index d6305a3..897e84e 100644
--- a/gcc/analyzer/svalue.cc
+++ b/gcc/analyzer/svalue.cc
@@ -481,6 +481,40 @@ svalue::cmp_ptr_ptr (const void *p1, const void *p2)
   return cmp_ptr (sval1, sval2);
 }
 
+/* Subclass of visitor for use in implementing svalue::involves_p.  */
+
+class involvement_visitor : public visitor
+{
+public:
+  involvement_visitor (const svalue *needle)
+  : m_needle (needle), m_found (false) {}
+
+  void visit_initial_svalue (const initial_svalue *candidate)
+  {
+    if (candidate == m_needle)
+      m_found = true;
+  }
+
+  bool found_p () const { return m_found; }
+
+private:
+  const svalue *m_needle;
+  bool m_found;
+};
+
+/* Return true iff this svalue is defined in terms of OTHER.  */
+
+bool
+svalue::involves_p (const svalue *other) const
+{
+  /* Currently only implemented for initial_svalue.  */
+  gcc_assert (other->get_kind () == SK_INITIAL);
+
+  involvement_visitor v (other);
+  accept (&v);
+  return v.found_p ();
+}
+
 /* class region_svalue : public svalue.  */
 
 /* Implementation of svalue::dump_to_pp vfunc for region_svalue.  */