analyzer: fix escaping of pointer arithmetic [PR105264]

PR analyzer/105264 reports that the analyzer can fail to treat
(PTR + IDX) and PTR[IDX] as referring to the same memory under
some situations.

There are various ways in which this can happen when IDX is a
symbolic value, due to having several ways in which such memory
regions can be referred to symbolically.  I attempted to fix this by
being smarter when folding svalues and regions, but this fix
seems too fiddly to attempt in stage 4.

Instead, this less ambitious patch fixes a false positive from
-Wanalyzer-use-of-uninitialized-value by making the analyzer's escape
analysis smarter, so that it treats *PTR as escaping when
(PTR + OFFSET) is passed to an external function, and thus
it treats *PTR as possibly-initialized (the "passing &PTR[IDX]" case
was already working).

gcc/analyzer/ChangeLog:
	PR analyzer/105264
	* region-model-reachability.cc (reachable_regions::handle_parm):
	Use maybe_get_deref_base_region rather than just region_svalue, to
	handle pointer arithmetic also.
	* svalue.cc (svalue::maybe_get_deref_base_region): New.
	* svalue.h (svalue::maybe_get_deref_base_region): New decl.

gcc/testsuite/ChangeLog:
	PR analyzer/105264
	* gcc.dg/analyzer/torture/symbolic-10.c: New test.

Signed-off-by: David Malcolm <dmalcolm@redhat.com>

1 files changed, 2 insertions, 6 deletions

diff --git a/gcc/analyzer/region-model-reachability.cc b/gcc/analyzer/region-model-reachability.cc
index b876b8f..12d09c3 100644
--- a/gcc/analyzer/region-model-reachability.cc
+++ b/gcc/analyzer/region-model-reachability.cc
@@ -252,12 +252,8 @@ reachable_regions::handle_parm (const svalue *sval, tree param_type)
     m_mutable_svals.add (sval);
   else
     m_reachable_svals.add (sval);
-  if (const region_svalue *parm_ptr
-      = sval->dyn_cast_region_svalue ())
-    {
-      const region *pointee_reg = parm_ptr->get_pointee ();
-      add (pointee_reg, is_mutable);
-    }
+  if (const region *base_reg = sval->maybe_get_deref_base_region ())
+    add (base_reg, is_mutable);
   /* Treat all svalues within a compound_svalue as reachable.  */
   if (const compound_svalue *compound_sval
       = sval->dyn_cast_compound_svalue ())