tree: Don't reuse types if TYPE_USER_ALIGN differ [PR94775]

Here we trip on the TYPE_USER_ALIGN (t) assert in strip_typedefs: it
gets "const d[0]" with TYPE_USER_ALIGN=0 but the result built by
build_cplus_array_type is "const char[0]" with TYPE_USER_ALIGN=1.

When we strip_typedefs the element of the array "const d", we see it's
a typedef_variant_p, so we look at its DECL_ORIGINAL_TYPE, which is
char, but we need to add the const qualifier, so we call
cp_build_qualified_type -> build_qualified_type
where get_qualified_type checks to see if we already have such a type
by walking the variants list, which in this case is:

  char -> c -> const char -> const char -> d -> const d

Because check_base_type only checks TYPE_ALIGN and not TYPE_USER_ALIGN,
we choose the first const char, which has TYPE_USER_ALIGN set.  If the
element type of an array has TYPE_USER_ALIGN, the array type gets it too.

So we can make check_base_type stricter.  I was afraid that it might make
us reuse types less often, but measuring showed that we build the same
amount of types with and without the patch, while bootstrapping.

	PR c++/94775
	* tree.c (check_base_type): Return true only if TYPE_USER_ALIGN match.
	(check_aligned_type): Check if TYPE_USER_ALIGN match.

	* g++.dg/warn/Warray-bounds-10.C: New test.

1 files changed, 3 insertions, 1 deletions

diff --git a/gcc/tree.c b/gcc/tree.c
index e451401..341766c 100644
--- a/gcc/tree.c
+++ b/gcc/tree.c
@@ -6493,7 +6493,8 @@ check_base_type (const_tree cand, const_tree base)
 			        TYPE_ATTRIBUTES (base)))
     return false;
   /* Check alignment.  */
-  if (TYPE_ALIGN (cand) == TYPE_ALIGN (base))
+  if (TYPE_ALIGN (cand) == TYPE_ALIGN (base)
+      && TYPE_USER_ALIGN (cand) == TYPE_USER_ALIGN (base))
     return true;
   /* Atomic types increase minimal alignment.  We must to do so as well
      or we get duplicated canonical types. See PR88686.  */
@@ -6528,6 +6529,7 @@ check_aligned_type (const_tree cand, const_tree base, unsigned int align)
 	  && TYPE_CONTEXT (cand) == TYPE_CONTEXT (base)
 	  /* Check alignment.  */
 	  && TYPE_ALIGN (cand) == align
+	  && TYPE_USER_ALIGN (cand) == TYPE_USER_ALIGN (base)
 	  && attribute_list_equal (TYPE_ATTRIBUTES (cand),
 				   TYPE_ATTRIBUTES (base))
 	  && check_lang_type (cand, base));