vrp: Handle pointers in maybe_set_nonzero_bits [PR108253]

maybe_set_nonzero_bits calls set_nonzero_bits which asserts that
var doesn't have pointer type.  While we could punt for those
cases, I think we can handle at least some easy cases.
Earlier in maybe_set_nonzero_bits we've checked this is on
(var & cst) == 0
edge and the other edge is __builtin_unreachable, so if cst
is say 3 as in the testcase, we want to turn it into 4 byte alignment
of the pointer.

2023-01-04  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/108253
	* tree-vrp.cc (maybe_set_nonzero_bits): Handle var with pointer
	types.

	* g++.dg/opt/pr108253.C: New test.

2 files changed, 64 insertions, 2 deletions

diff --git a/gcc/testsuite/g++.dg/opt/pr108253.C b/gcc/testsuite/g++.dg/opt/pr108253.C
new file mode 100644
index 0000000..0409121
--- /dev/null
+++ b/gcc/testsuite/g++.dg/opt/pr108253.C
@@ -0,0 +1,48 @@
+// PR tree-optimization/108253
+// { dg-do compile { target c++11 } }
+// { dg-options "-O2" }
+
+struct S
+{
+  int *s;
+  S () : s (new int) {}
+  S (const S &r) noexcept : s (r.s) { __atomic_fetch_add (r.s, 1, 4); }
+};
+struct T
+{
+  explicit T (const S &x) : t (x) {}
+  const S t;
+};
+struct U
+{
+  operator int () const { new T (u); return 0; }
+  S u;
+};
+bool foo (int matcher);
+unsigned long bar (unsigned long pos, unsigned long end_pos);
+struct V
+{
+  alignas (4) char v[4];
+};
+struct W
+{
+  void baz ()
+  {
+    if (!w) __builtin_abort ();
+    if (reinterpret_cast <__UINTPTR_TYPE__> (w->v) % 4 != 0) __builtin_abort ();
+    __builtin_unreachable ();
+  }
+  [[gnu::noinline]] void qux (unsigned long) { if (!w) bar (0, x); } 
+  V *w = nullptr;
+  unsigned x = 0;
+};
+
+void
+test ()
+{
+  W w;
+  U t;
+  if (!foo (t))
+    w.baz ();
+  w.qux (0);
+}
diff --git a/gcc/tree-vrp.cc b/gcc/tree-vrp.cc
index 0dfea5a..3c43176 100644
--- a/gcc/tree-vrp.cc
+++ b/gcc/tree-vrp.cc
@@ -789,8 +789,22 @@ maybe_set_nonzero_bits (edge e, tree var)
 	return;
     }
   cst = gimple_assign_rhs2 (stmt);
-  set_nonzero_bits (var, wi::bit_and_not (get_nonzero_bits (var),
-					  wi::to_wide (cst)));
+  if (POINTER_TYPE_P (TREE_TYPE (var)))
+    {
+      struct ptr_info_def *pi = SSA_NAME_PTR_INFO (var);
+      if (pi && pi->misalign)
+	return;
+      wide_int w = wi::bit_not (wi::to_wide (cst));
+      unsigned int bits = wi::ctz (w);
+      if (bits == 0 || bits >= HOST_BITS_PER_INT)
+	return;
+      unsigned int align = 1U << bits;
+      if (pi == NULL || pi->align < align)
+	set_ptr_info_alignment (get_ptr_info (var), align, 0);
+    }
+  else
+    set_nonzero_bits (var, wi::bit_and_not (get_nonzero_bits (var),
+					    wi::to_wide (cst)));
 }
 
 /* Searches the case label vector VEC for the index *IDX of the CASE_LABEL