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.

4 files changed, 54 insertions, 1 deletions

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index c6e2447..f83e7ac 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,9 @@
+2020-04-30  Marek Polacek  <polacek@redhat.com>
+
+	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.
+
 2020-04-30  Kyrylo Tkachov  <kyrylo.tkachov@arm.com>
 
 	* config/aarch64/aarch64.h (TARGET_OUTLINE_ATOMICS): Define.
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 66ac670..49f0042 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,8 @@
+2020-04-30  Marek Polacek  <polacek@redhat.com>
+
+	PR c++/94775
+	* g++.dg/warn/Warray-bounds-10.C: New test.
+
 2020-04-30  Szabolcs Nagy  <szabolcs.nagy@arm.com>
 
 	PR target/94748
diff --git a/gcc/testsuite/g++.dg/warn/Warray-bounds-10.C b/gcc/testsuite/g++.dg/warn/Warray-bounds-10.C
new file mode 100644
index 0000000..0a18f63
--- /dev/null
+++ b/gcc/testsuite/g++.dg/warn/Warray-bounds-10.C
@@ -0,0 +1,40 @@
+// PR c++/94775
+// { dg-do compile { target c++14 } }
+// { dg-options "-O2 -Warray-bounds" }
+
+template <typename> using a = int;
+template <bool, typename, typename> using b = int;
+typedef char d;
+template <long> using e = int;
+template <int f, int q> struct h { using i = b<q, a<e<f>>, e<f>>; };
+template <long f, bool g> using j = typename h<f, g>::i;
+long ab, k, aj;
+const d l[]{};
+class m {
+public:
+  m(int);
+};
+class n {
+  void ad() const;
+  template <class ae> void o(long) const {
+    using c __attribute__((aligned(1))) = const ae;
+  }
+  long p;
+  template <class, class>
+  auto s(unsigned long, unsigned long, unsigned long, unsigned long) const;
+  template <bool = false> auto q(unsigned long, unsigned long) const;
+};
+template <class, class>
+auto n::s(unsigned long, unsigned long, unsigned long, unsigned long t) const {
+  o<d>(p);
+  return t;
+}
+template <bool g> auto n::q(unsigned long p1, unsigned long p2) const {
+  using r = j<4, false>;
+  using ai = j<4, g>;
+  return s<ai, r>(ab, k, p1, p2);
+}
+void n::ad() const {
+  long f(l[aj]); // { dg-warning "outside array bounds" }
+  m(q(8, f));
+}
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));