c++: fix 'unsigned typedef-name' extension [PR108099]

In the comments for PR108099 Jakub provided some testcases that demonstrated
that even before the regression noted in the patch we were getting the
semantics of this extension wrong: in the unsigned case we weren't producing
the corresponding standard unsigned type but another distinct one of the
same size, and in the signed case we were just dropping it on the floor and
not actually returning a signed type at all.

The former issue is fixed by using c_common_signed_or_unsigned_type instead
of unsigned_type_for, and the latter issue by adding a (signed_p &&
typedef_decl) case.

This patch introduces a failure on std/ranges/iota/max_size_type.cc due to
the latter issue, since the testcase expects 'signed rep_t' to do something
sensible, and previously we didn't.  Now that we do, it exposes a bug in the
__max_diff_type::operator>>= handling of sign extension: when we evaluate
-1000 >> 2 in __max_diff_type we keep the MSB set, but leave the
second-most-significant bit cleared.

	PR c++/108099

gcc/cp/ChangeLog:

	* decl.cc (grokdeclarator): Don't clear typedef_decl after 'unsigned
	typedef' pedwarn.  Use c_common_signed_or_unsigned_type.  Also
	handle 'signed typedef'.

gcc/testsuite/ChangeLog:

	* g++.dg/ext/int128-8.C: Remove xfailed dg-bogus markers.
	* g++.dg/ext/unsigned-typedef2.C: New test.
	* g++.dg/ext/unsigned-typedef3.C: New test.

4 files changed, 60 insertions, 12 deletions

diff --git a/gcc/cp/decl.cc b/gcc/cp/decl.cc
index ab5cb69..71d33d2 100644
--- a/gcc/cp/decl.cc
+++ b/gcc/cp/decl.cc
@@ -12478,18 +12478,14 @@ grokdeclarator (const cp_declarator *declarator,
 	{
 	  if (typedef_decl)
 	    {
-	      pedwarn (loc, OPT_Wpedantic, "%qs specified with %qD",
+	      pedwarn (loc, OPT_Wpedantic,
+		       "%qs specified with typedef-name %qD",
 		       key, typedef_decl);
 	      ok = !flag_pedantic_errors;
+	      /* PR108099: __int128_t comes from c_common_nodes_and_builtins,
+		 and is not built as a typedef.  */
 	      if (is_typedef_decl (typedef_decl))
-		{
-		  type = DECL_ORIGINAL_TYPE (typedef_decl);
-		  typedef_decl = NULL_TREE;
-		}
-	      else
-		/* PR108099: __int128_t comes from c_common_nodes_and_builtins,
-		   and is not built as a typedef.  */
-		type = TREE_TYPE (typedef_decl);
+		type = DECL_ORIGINAL_TYPE (typedef_decl);
 	    }
 	  else if (declspecs->decltype_p)
 	    error_at (loc, "%qs specified with %<decltype%>", key);
@@ -12542,7 +12538,7 @@ grokdeclarator (const cp_declarator *declarator,
       else if (type == char_type_node)
 	type = unsigned_char_type_node;
       else if (typedef_decl)
-	type = unsigned_type_for (type);
+	type = c_common_unsigned_type (type);
       else
 	type = unsigned_type_node;
     }
@@ -12556,6 +12552,8 @@ grokdeclarator (const cp_declarator *declarator,
     type = long_integer_type_node;
   else if (short_p)
     type = short_integer_type_node;
+  else if (signed_p && typedef_decl)
+    type = c_common_signed_type (type);
 
   if (decl_spec_seq_has_spec_p (declspecs, ds_complex))
     {
diff --git a/gcc/testsuite/g++.dg/ext/int128-8.C b/gcc/testsuite/g++.dg/ext/int128-8.C
index 7e909d5..07535a9 100644
--- a/gcc/testsuite/g++.dg/ext/int128-8.C
+++ b/gcc/testsuite/g++.dg/ext/int128-8.C
@@ -16,8 +16,8 @@ struct is_same <T, T> : true_type {};
 static_assert (is_same <__int128, s128>::value, "");
 static_assert (is_same <signed __int128, s128>::value, "");
 static_assert (is_same <__int128_t, s128>::value, "");
-static_assert (is_same <unsigned __int128, u128>::value, ""); // { dg-bogus "" "" { xfail *-*-* } }
-static_assert (is_same <__uint128_t, u128>::value, "");	      // { dg-bogus "" "" { xfail *-*-* } }
+static_assert (is_same <unsigned __int128, u128>::value, "");
+static_assert (is_same <__uint128_t, u128>::value, "");
 static_assert (sizeof (s128) == sizeof (__int128), "");
 static_assert (sizeof (u128) == sizeof (unsigned __int128), "");
 static_assert (s128(-1) < 0, "");
diff --git a/gcc/testsuite/g++.dg/ext/unsigned-typedef2.C b/gcc/testsuite/g++.dg/ext/unsigned-typedef2.C
new file mode 100644
index 0000000..936c0cc
--- /dev/null
+++ b/gcc/testsuite/g++.dg/ext/unsigned-typedef2.C
@@ -0,0 +1,25 @@
+// PR c++/108099
+// { dg-do compile { target c++11 } }
+// { dg-options "" }
+
+typedef long long t64;
+template <typename T, T v> struct integral_constant {
+  static constexpr T value = v;
+};
+typedef integral_constant <bool, false> false_type;
+typedef integral_constant <bool, true> true_type;
+template <class T, class U>
+struct is_same : false_type {};
+template <class T>
+struct is_same <T, T> : true_type {};
+
+using s64 = signed t64;
+static_assert (is_same <long long, s64>::value, "");
+static_assert (is_same <signed long long, s64>::value, "");
+static_assert (sizeof (s64) == sizeof (long long), "");
+static_assert (s64(-1) < 0, "");
+
+using u64 = unsigned t64;
+static_assert (is_same <unsigned long long, u64>::value, "");
+static_assert (sizeof (u64) == sizeof (unsigned long long), "");
+static_assert (u64(-1) > 0, "");
diff --git a/gcc/testsuite/g++.dg/ext/unsigned-typedef3.C b/gcc/testsuite/g++.dg/ext/unsigned-typedef3.C
new file mode 100644
index 0000000..bb99ca0
--- /dev/null
+++ b/gcc/testsuite/g++.dg/ext/unsigned-typedef3.C
@@ -0,0 +1,25 @@
+// PR c++/108099
+// { dg-do compile { target c++11 } }
+// { dg-options "" }
+
+typedef unsigned long long t64;
+template <typename T, T v> struct integral_constant {
+  static constexpr T value = v;
+};
+typedef integral_constant <bool, false> false_type;
+typedef integral_constant <bool, true> true_type;
+template <class T, class U>
+struct is_same : false_type {};
+template <class T>
+struct is_same <T, T> : true_type {};
+
+using s64 = signed t64;
+static_assert (is_same <long long, s64>::value, "");
+static_assert (is_same <signed long long, s64>::value, "");
+static_assert (sizeof (s64) == sizeof (long long), "");
+static_assert (s64(-1) < 0, "");
+
+using u64 = unsigned t64;
+static_assert (is_same <unsigned long long, u64>::value, "");
+static_assert (sizeof (u64) == sizeof (unsigned long long), "");
+static_assert (u64(-1) > 0, "");