[gcc r13-7277] c++: fix 'unsigned typedef-name' extension [PR108099]

[gcc r13-7277] c++: fix 'unsigned typedef-name' extension [PR108099]

[Jason Merrill]

https://gcc.gnu.org/g:a713aa4f47ac1efbfe2338790b0b5e94a233fb99

commit r13-7277-ga713aa4f47ac1efbfe2338790b0b5e94a233fb99
Author: Jason Merrill <jason@redhat.com>
Date:   Tue Apr 18 21:32:07 2023 -0400

    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: New test.
            * g++.dg/ext/unsigned-typedef2.C: New test.
            * g++.dg/ext/unsigned-typedef3.C: New test.

Diff:
---
 gcc/cp/decl.cc                               | 14 +++++++-------
 gcc/testsuite/g++.dg/ext/int128-8.C          | 24 ++++++++++++++++++++++++
 gcc/testsuite/g++.dg/ext/unsigned-typedef2.C | 25 +++++++++++++++++++++++++
 gcc/testsuite/g++.dg/ext/unsigned-typedef3.C | 25 +++++++++++++++++++++++++
 4 files changed, 81 insertions(+), 7 deletions(-)

diff --git a/gcc/cp/decl.cc b/gcc/cp/decl.cc
index 772c059dc2c..71d33d2b7a4 100644
--- a/gcc/cp/decl.cc
+++ b/gcc/cp/decl.cc
@@ -12478,16 +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);
-	      else
-		/* PR108099: __int128_t comes from c_common_nodes_and_builtins,
-		   and is not built as a typedef.  */
-		type = TREE_TYPE (typedef_decl);
-	      typedef_decl = NULL_TREE;
 	    }
 	  else if (declspecs->decltype_p)
 	    error_at (loc, "%qs specified with %<decltype%>", key);
@@ -12540,7 +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;
     }
@@ -12554,6 +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
new file mode 100644
index 00000000000..07535a9820e
--- /dev/null
+++ b/gcc/testsuite/g++.dg/ext/int128-8.C
@@ -0,0 +1,24 @@
+// PR c++/108099
+// { dg-do compile { target { c++11 && int128 } } }
+// { dg-options "" }
+
+using u128 = unsigned __int128_t;
+using s128 = signed __int128_t;
+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 {};
+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, "");
+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, "");
+static_assert (u128(-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 00000000000..936c0ccb748
--- /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 00000000000..bb99ca0ccc9
--- /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, "");