[PATCH v3 1/2] Fix type compatibility for types with flexible array member [PR113688,PR114713,PR117724]

[Martin Uecker]

As requested, I split up into one part for the TYPE_MODE and 
another one for the array size to help with git bisecting.  This
is the first part.


Bootstrapped and regression tested on x86_64.



Allow the TYPE_MODE of a type with an array as last member to differ from
another compatible type.

gcc/ChangeLog:
        * tree.cc (gimple_canonical_types_compatible_p): Add exception.
        (verify_type): Add exception.

gcc/lto/ChangeLog:
        * lto-common.cc (hash_canonical_type): Add exception.
---
 gcc/lto/lto-common.cc |  3 ++-
 gcc/tree.cc           | 12 +++++++++---
 2 files changed, 11 insertions(+), 4 deletions(-)

diff --git a/gcc/lto/lto-common.cc b/gcc/lto/lto-common.cc
index 86a309f92b4..94050209912 100644
--- a/gcc/lto/lto-common.cc
+++ b/gcc/lto/lto-common.cc
@@ -254,7 +254,8 @@ hash_canonical_type (tree type)
      checked.  */
   code = tree_code_for_canonical_type_merging (TREE_CODE (type));
   hstate.add_int (code);
-  hstate.add_int (TYPE_MODE (type));
+  if (!RECORD_OR_UNION_TYPE_P (type))
+    hstate.add_int (TYPE_MODE (type));
 
   /* Incorporate common features of numerical types.  */
   if (INTEGRAL_TYPE_P (type)
diff --git a/gcc/tree.cc b/gcc/tree.cc
index 83a03374a32..1391af6bd4c 100644
--- a/gcc/tree.cc
+++ b/gcc/tree.cc
@@ -13914,8 +13914,11 @@ gimple_canonical_types_compatible_p (const_tree t1, 
const_tree t2,
       || TREE_CODE (t1) == NULLPTR_TYPE)
     return true;
 
-  /* Can't be the same type if they have different mode.  */
-  if (TYPE_MODE (t1) != TYPE_MODE (t2))
+  /* Can't be compatible types if they have different mode.  Because of
+     flexible array members, we allow mismatching modes for structures or
+     unions.  */
+  if (!RECORD_OR_UNION_TYPE_P (t1)
+      && TYPE_MODE (t1) != TYPE_MODE (t2))
     return false;
 
   /* Non-aggregate types can be handled cheaply.  */
@@ -14218,8 +14221,11 @@ verify_type (const_tree t)
       debug_tree (ct);
       error_found = true;
     }
-
   if (COMPLETE_TYPE_P (t) && TYPE_CANONICAL (t)
+      /* We allow a mismatch for structure or union because of
+        flexible array members.  */
+      && !RECORD_OR_UNION_TYPE_P (t)
+      && !RECORD_OR_UNION_TYPE_P (TYPE_CANONICAL (t))
       && TYPE_MODE (t) != TYPE_MODE (TYPE_CANONICAL (t)))
     {
       error ("%<TYPE_MODE%> of %<TYPE_CANONICAL%> is not compatible");
-- 
2.39.5