[PATCH] c++: Don't add built-in operator for ++ on bool.

[Marek Polacek via Gcc-patches]

This feels extremely obscure but at least it's an opportunity to fix the
comments.  P0002R1 removed deprecated operator++(bool) in C++17 so let's
avoid adding a builtin overload candidate for ++ when the type is bool.

Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?

        * call.c (add_builtin_candidate): Don't create a builtin overload
        candidate for ++ when type is bool in C++17.

        * g++.dg/overload/builtin5.C: New test.
---
 gcc/cp/call.c                            | 18 +++++++++++-------
 gcc/testsuite/g++.dg/overload/builtin5.C | 21 +++++++++++++++++++++
 2 files changed, 32 insertions(+), 7 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/overload/builtin5.C

diff --git a/gcc/cp/call.c b/gcc/cp/call.c
index c5871974eb1..b96bc06a364 100644
--- a/gcc/cp/call.c
+++ b/gcc/cp/call.c
@@ -2672,19 +2672,19 @@ add_builtin_candidate (struct z_candidate **candidates, 
enum tree_code code,
   switch (code)
     {
 
-/* 4 For every pair T, VQ), where T is an arithmetic or  enumeration  type,
+/* 4 For every pair (T, VQ), where T is an arithmetic type other than bool,
      and  VQ  is  either  volatile or empty, there exist candidate operator
      functions of the form
             VQ T&   operator++(VQ T&);
             T       operator++(VQ T&, int);
-   5 For every pair T, VQ), where T is an enumeration type or an arithmetic
-     type  other than bool, and VQ is either volatile or empty, there exist
-     candidate operator functions of the form
+   5 For every pair (T, VQ), where T is an arithmetic type other than bool,
+     and VQ is either volatile or empty, there exist candidate operator
+     functions of the form
             VQ T&   operator--(VQ T&);
             T       operator--(VQ T&, int);
-   6 For every pair T, VQ), where T is  a  cv-qualified  or  cv-unqualified
-     complete  object type, and VQ is either volatile or empty, there exist
-     candidate operator functions of the form
+   6 For every pair (T, VQ), where T is a cv-qualified or cv-unqualified object
+     type, and VQ is either volatile or empty, there exist candidate operator
+     functions of the form
             T*VQ&   operator++(T*VQ&);
             T*VQ&   operator--(T*VQ&);
             T*      operator++(T*VQ&, int);
@@ -2697,6 +2697,10 @@ add_builtin_candidate (struct z_candidate **candidates, 
enum tree_code code,
       /* FALLTHRU */
     case POSTINCREMENT_EXPR:
     case PREINCREMENT_EXPR:
+      /* P0002R1, Remove deprecated operator++(bool) added "other than bool"
+        to p4.  */
+      if (TREE_CODE (type1) == BOOLEAN_TYPE && cxx_dialect >= cxx17)
+       return;
       if (ARITHMETIC_TYPE_P (type1) || TYPE_PTROB_P (type1))
        {
          type1 = build_reference_type (type1);
diff --git a/gcc/testsuite/g++.dg/overload/builtin5.C 
b/gcc/testsuite/g++.dg/overload/builtin5.C
new file mode 100644
index 00000000000..a30251dc79d
--- /dev/null
+++ b/gcc/testsuite/g++.dg/overload/builtin5.C
@@ -0,0 +1,21 @@
+// { dg-do compile { target c++17 } }
+// Don't add built-in operator for ++ on bool.
+
+template<typename T>
+struct S { operator T&(); };
+
+template<int> void
+foo (S<bool>& s)
+{
+  --s; // { dg-error "no match for" }
+  ++s; // { dg-error "no match for" }
+  s++; // { dg-error "declared for postfix" }
+  s--; // { dg-error "declared for postfix" }
+}
+
+void
+bar ()
+{
+  S<bool> s;
+  foo<0> (s);
+}

base-commit: f5b461d453043c6b6dda50db0439e4c78b241f03
-- 
Marek Polacek • Red Hat, Inc. • 300 A St, Boston, MA