analyzer: handle empty ranges in symbolic_byte_range::intersection [PR113998]

gcc/analyzer/ChangeLog:
	PR analyzer/113998
	* ranges.cc (symbolic_byte_range::intersection): Handle empty ranges.
	(selftest::test_intersects): Add test coverage for empty ranges.

gcc/testsuite/ChangeLog:
	PR analyzer/113998
	* c-c++-common/analyzer/overlapping-buffers-pr113998.c: New test.

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

2 files changed, 39 insertions, 0 deletions

diff --git a/gcc/analyzer/ranges.cc b/gcc/analyzer/ranges.cc
index f46b041..ffdd0d4 100644
--- a/gcc/analyzer/ranges.cc
+++ b/gcc/analyzer/ranges.cc
@@ -193,6 +193,12 @@ tristate
 symbolic_byte_range::intersection (const symbolic_byte_range &other,
 				   const region_model &model) const
 {
+  /* If either is empty, then there is no intersection.  */
+  if (empty_p ())
+    return tristate::TS_FALSE;
+  if (other.empty_p ())
+    return tristate::TS_FALSE;
+
   /* For brevity, consider THIS to be "range A", and OTHER to be "range B".  */
 
   region_model_manager *mgr = model.get_manager ();
@@ -262,12 +268,17 @@ static void test_intersects (void)
   ASSERT_EQ (r0_9.get_next_byte_offset (mgr), ten);
   ASSERT_EQ (r0_9.get_last_byte_offset (mgr), nine);
 
+  symbolic_byte_range concrete_empty (zero, zero);
+  ASSERT_TRUE (concrete_empty.empty_p ());
+
   ASSERT_EQ (r0_9.intersection (r0, m), tristate::TS_TRUE);
   ASSERT_EQ (r0.intersection (r0_9, m), tristate::TS_TRUE);
   ASSERT_EQ (r0_9.intersection (r9, m), tristate::TS_TRUE);
   ASSERT_EQ (r9.intersection (r0_9, m), tristate::TS_TRUE);
   ASSERT_EQ (r0_9.intersection (r10, m), tristate::TS_FALSE);
   ASSERT_EQ (r10.intersection (r0_9, m), tristate::TS_FALSE);
+  ASSERT_EQ (concrete_empty.intersection (r0_9, m), tristate::TS_FALSE);
+  ASSERT_EQ (r0_9.intersection (concrete_empty, m), tristate::TS_FALSE);
 
   ASSERT_EQ (r5_9.intersection (r0, m), tristate::TS_FALSE);
   ASSERT_EQ (r0.intersection (r5_9, m), tristate::TS_FALSE);
@@ -286,6 +297,9 @@ static void test_intersects (void)
   symbolic_byte_range ry (y_init_sval, one);
   symbolic_byte_range rx_x_plus_y_minus_1 (x_init_sval, y_init_sval);
 
+  symbolic_byte_range symbolic_empty (x_init_sval, zero);
+  ASSERT_TRUE (symbolic_empty.empty_p ());
+
   ASSERT_EQ (rx_x_plus_y_minus_1.get_start_byte_offset (), x_init_sval);
   ASSERT_EQ (rx_x_plus_y_minus_1.get_size_in_bytes (), y_init_sval);
   ASSERT_EQ
@@ -296,6 +310,10 @@ static void test_intersects (void)
      SK_BINOP);
 
   ASSERT_EQ (rx.intersection (ry, m), tristate::TS_UNKNOWN);
+  ASSERT_EQ (rx.intersection (concrete_empty, m), tristate::TS_FALSE);
+  ASSERT_EQ (concrete_empty.intersection (rx, m), tristate::TS_FALSE);
+  ASSERT_EQ (rx.intersection (symbolic_empty, m), tristate::TS_FALSE);
+  ASSERT_EQ (symbolic_empty.intersection (rx, m), tristate::TS_FALSE);
   ASSERT_EQ (r0_x_minus_1.intersection (r0, m), tristate::TS_TRUE);
 #if 0
   ASSERT_EQ (r0_x_minus_1.intersection (rx, m), tristate::TS_FALSE);
diff --git a/gcc/testsuite/c-c++-common/analyzer/overlapping-buffers-pr113998.c b/gcc/testsuite/c-c++-common/analyzer/overlapping-buffers-pr113998.c
new file mode 100644
index 0000000..5c6352e
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/analyzer/overlapping-buffers-pr113998.c
@@ -0,0 +1,21 @@
+/* Verify we don't ICE on -Wanalyzer-overlapping-buffers on
+   execution paths where the size is constant zero, but the
+   optimizer didn't see that.  */
+
+typedef __SIZE_TYPE__ size_t;
+
+extern char a[];
+size_t n;
+
+size_t  __attribute__((noinline))
+get_hidden_zero ()
+{
+  return 0;
+}
+
+void
+test_pr113998 ()
+{
+  size_t n = get_hidden_zero ();
+  __builtin_strncpy (a, a, n); /* { dg-warning "overlapping buffers passed as arguments to" } */
+}