[gcc(refs/vendors/ARM/heads/morello)] cp: Explicitly null-derive some pointers

[gcc(refs/vendors/ARM/heads/morello)] cp: Explicitly null-derive some pointers

[Matthew Malcomson]

https://gcc.gnu.org/g:f58ba93e83426e0c296e71b19eac7a64cfdc2cf5

commit f58ba93e83426e0c296e71b19eac7a64cfdc2cf5
Author: Alex Coplan <alex.coplan@arm.com>
Date:   Fri Jan 28 16:17:42 2022 +0000

    cp: Explicitly null-derive some pointers
    
    The C++ frontend sometimes constructs pointers from constant integers by
    directly converting them. This patch null-derives these instead in a
    couple of places to avoid ICEs.
    
    gcc/cp/ChangeLog:
    
            * class.c (build_rtti_vtbl_entries): We can't simply convert
            integers into capability pointers: null-derive these instead
            (e.g. when putting an offset into a vtable).
            * method.c (build_stub_object): When building our dummy
            reference, null-derive a capability instead of just trying to
            convert integer_one_node into a capability type.

Diff:
---
 gcc/cp/class.c  | 7 ++++++-
 gcc/cp/method.c | 9 ++++++++-
 2 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/gcc/cp/class.c b/gcc/cp/class.c
index b39bdaaa3ab..0202216ad39 100644
--- a/gcc/cp/class.c
+++ b/gcc/cp/class.c
@@ -10209,7 +10209,9 @@ build_rtti_vtbl_entries (tree binfo, vtbl_init_data* vid)
   if (flag_rtti)
     decl = build_address (get_tinfo_decl (t));
   else
-    decl = integer_zero_node;
+    decl = capability_type_p (vfunc_ptr_type_node)
+      ? null_pointer_node
+      : integer_zero_node;
 
   /* Convert the declaration to a type that can be stored in the
      vtable.  */
@@ -10219,6 +10221,9 @@ build_rtti_vtbl_entries (tree binfo, vtbl_init_data* vid)
   /* Add the offset-to-top entry.  It comes earlier in the vtable than
      the typeinfo entry.  Convert the offset to look like a
      function pointer, so that we can put it in the vtable.  */
+  if (capability_type_p (vfunc_ptr_type_node))
+    offset = fold_build_pointer_plus (null_pointer_node, offset);
+
   init = build_nop (vfunc_ptr_type_node, offset);
   CONSTRUCTOR_APPEND_ELT (vid->inits, NULL_TREE, init);
 }
diff --git a/gcc/cp/method.c b/gcc/cp/method.c
index 1058fd05a7d..ae154ef2872 100644
--- a/gcc/cp/method.c
+++ b/gcc/cp/method.c
@@ -1627,7 +1627,14 @@ build_stub_object (tree reftype)
 {
   if (!TYPE_REF_P (reftype))
     reftype = cp_build_reference_type (reftype, /*rval*/true);
-  tree stub = build1 (CONVERT_EXPR, reftype, integer_one_node);
+
+  tree one = integer_one_node;
+
+  /* For purecap, we must explicitly null-derive the capability.  */
+  if (capability_type_p (reftype))
+    one = fold_build_pointer_plus (null_pointer_node, one);
+
+  tree stub = build1 (CONVERT_EXPR, reftype, one);
   return convert_from_reference (stub);
 }