analyzer: fix ICE for 2 bits before the start of base region [PR112889]

Cncrete bindings were using -1 and -2 in the offset field to signify
deleted and empty hash slots, but these are valid values, leading to
assertion failures inside hash_map::put on a debug build, and probable
bugs in a release build.

(gdb) call k.dump(true)
start: -2, size: 1, next: -1

(gdb) p k.is_empty()
$6 = true

Fix by using the size field rather than the offset.

Backported from commit r14-6297-g775aeabcb870b7 (moving the testcase
from c-c++-common to gcc.dg).

gcc/analyzer/ChangeLog:
	PR analyzer/112889
	* store.h (concrete_binding::concrete_binding): Strengthen
	assertion to require size to be be positive, rather than just
	non-zero.
	(concrete_binding::mark_deleted): Use size rather than start bit
	offset.
	(concrete_binding::mark_empty): Likewise.
	(concrete_binding::is_deleted): Likewise.
	(concrete_binding::is_empty): Likewise.

gcc/testsuite/ChangeLog:
	PR analyzer/112889
	* gcc.dg/analyzer/ice-pr112889.c: New test.

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

2 files changed, 22 insertions, 5 deletions

diff --git a/gcc/analyzer/store.h b/gcc/analyzer/store.h
index 7ded650..6b06be2 100644
--- a/gcc/analyzer/store.h
+++ b/gcc/analyzer/store.h
@@ -368,7 +368,7 @@ public:
   concrete_binding (bit_offset_t start_bit_offset, bit_size_t size_in_bits)
   : m_bit_range (start_bit_offset, size_in_bits)
   {
-    gcc_assert (!m_bit_range.empty_p ());
+    gcc_assert (m_bit_range.m_size_in_bits > 0);
   }
   bool concrete_p () const final override { return true; }
 
@@ -409,10 +409,10 @@ public:
 
   static int cmp_ptr_ptr (const void *, const void *);
 
-  void mark_deleted () { m_bit_range.m_start_bit_offset = -1; }
-  void mark_empty () { m_bit_range.m_start_bit_offset = -2; }
-  bool is_deleted () const { return m_bit_range.m_start_bit_offset == -1; }
-  bool is_empty () const { return m_bit_range.m_start_bit_offset == -2; }
+  void mark_deleted () { m_bit_range.m_size_in_bits = -1; }
+  void mark_empty () { m_bit_range.m_size_in_bits = -2; }
+  bool is_deleted () const { return m_bit_range.m_size_in_bits == -1; }
+  bool is_empty () const { return m_bit_range.m_size_in_bits == -2; }
 
 private:
   bit_range m_bit_range;
diff --git a/gcc/testsuite/gcc.dg/analyzer/ice-pr112889.c b/gcc/testsuite/gcc.dg/analyzer/ice-pr112889.c
new file mode 100644
index 0000000..e90a53e
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/analyzer/ice-pr112889.c
@@ -0,0 +1,17 @@
+typedef unsigned char __u8;
+struct sk_buff
+{
+  unsigned char *data;
+};
+struct cpl_pass_accept_req
+{
+  __u8 : 6;
+  __u8 sack : 1;
+};
+void build_cpl_pass_accept_req(struct sk_buff* skb)
+{
+  struct cpl_pass_accept_req* req;
+  skb->data -= sizeof(*req);
+  req = (struct cpl_pass_accept_req *)skb->data;
+  req->sack = 1;
+}