[PATCH] Reorder conditions in uses-allocator construction helper

[PATCH] Reorder conditions in uses-allocator construction helper

[Jonathan Wakely]

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The erased_type condition is only true for code using the Library
Fundamentals TS, so assume it's less common and only check it after
checking for convertibility.

This does mean for types using erased_type the more expensive
convertibility check is done first, but such types are rare.

	* include/bits/uses_allocator.h (__is_erased_or_convertible): Reorder
	conditions. Add comments.
	* testsuite/20_util/uses_allocator/69293_neg.cc: Adjust dg-error line.
	* testsuite/20_util/uses_allocator/cons_neg.cc: Likewise.
	* testsuite/20_util/scoped_allocator/69293_neg.cc: Likewise.

Tested powerpc64le-linux, committed to trunk.



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commit baf0d8cca17bc1223580b416c501f4b74bbca9b3
Author: redi <redi@138bc75d-0d04-0410-961f-82ee72b054a4>
Date:   Tue Jul 24 13:03:25 2018 +0000

    Reorder conditions in uses-allocator construction helper
    
    The erased_type condition is only true for code using the Library
    Fundamentals TS, so assume it's less common and only check it after
    checking for convertibility.
    
    This does mean for types using erased_type the more expensive
    convertibility check is done first, but such types are rare.
    
            * include/bits/uses_allocator.h (__is_erased_or_convertible): Reorder
            conditions. Add comments.
            * testsuite/20_util/uses_allocator/69293_neg.cc: Adjust dg-error line.
            * testsuite/20_util/uses_allocator/cons_neg.cc: Likewise.
            * testsuite/20_util/scoped_allocator/69293_neg.cc: Likewise.
    
    git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@262945 138bc75d-0d04-0410-961f-82ee72b054a4

diff --git a/libstdc++-v3/include/bits/uses_allocator.h b/libstdc++-v3/include/bits/uses_allocator.h
index 820a2a59894..3ef2830bebc 100644
--- a/libstdc++-v3/include/bits/uses_allocator.h
+++ b/libstdc++-v3/include/bits/uses_allocator.h
@@ -36,11 +36,15 @@ namespace std _GLIBCXX_VISIBILITY(default)
 {
 _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
+  // This is used for std::experimental::erased_type from Library Fundamentals.
   struct __erased_type { };
 
+  // This also supports the "type-erased allocator" protocol from the
+  // Library Fundamentals TS, where allocator_type is erased_type.
+  // The second condition will always be false for types not using the TS.
   template<typename _Alloc, typename _Tp>
     using __is_erased_or_convertible
-      = __or_<is_same<_Tp, __erased_type>, is_convertible<_Alloc, _Tp>>;
+      = __or_<is_convertible<_Alloc, _Tp>, is_same<_Tp, __erased_type>>;
 
   /// [allocator.tag]
   struct allocator_arg_t { explicit allocator_arg_t() = default; };
diff --git a/libstdc++-v3/testsuite/20_util/scoped_allocator/69293_neg.cc b/libstdc++-v3/testsuite/20_util/scoped_allocator/69293_neg.cc
index 621ff47c7a3..168079fd5f9 100644
--- a/libstdc++-v3/testsuite/20_util/scoped_allocator/69293_neg.cc
+++ b/libstdc++-v3/testsuite/20_util/scoped_allocator/69293_neg.cc
@@ -46,5 +46,5 @@ test01()
   scoped_alloc sa;
   auto p = sa.allocate(1);
   sa.construct(p);  // this is required to be ill-formed
-  // { dg-error "static assertion failed" "" { target *-*-* } 90 }
+  // { dg-error "static assertion failed" "" { target *-*-* } 94 }
 }
diff --git a/libstdc++-v3/testsuite/20_util/uses_allocator/69293_neg.cc b/libstdc++-v3/testsuite/20_util/uses_allocator/69293_neg.cc
index 348ed41a7bc..eaf432491c6 100644
--- a/libstdc++-v3/testsuite/20_util/uses_allocator/69293_neg.cc
+++ b/libstdc++-v3/testsuite/20_util/uses_allocator/69293_neg.cc
@@ -44,5 +44,5 @@ test01()
 {
   alloc_type a;
   std::tuple<X> t(std::allocator_arg, a); // this is required to be ill-formed
-  // { dg-error "static assertion failed" "" { target *-*-* } 90 }
+  // { dg-error "static assertion failed" "" { target *-*-* } 94 }
 }
diff --git a/libstdc++-v3/testsuite/20_util/uses_allocator/cons_neg.cc b/libstdc++-v3/testsuite/20_util/uses_allocator/cons_neg.cc
index 8894e389cec..bb8c38d1e49 100644
--- a/libstdc++-v3/testsuite/20_util/uses_allocator/cons_neg.cc
+++ b/libstdc++-v3/testsuite/20_util/uses_allocator/cons_neg.cc
@@ -43,4 +43,4 @@ void test01()
 
   tuple<Type> t(allocator_arg, a, 1);
 }
-// { dg-error "static assertion failed" "" { target *-*-* } 90 }
+// { dg-error "static assertion failed" "" { target *-*-* } 94 }