From 088e6015b20fd097f7b00bb330c359added2c9c5 Mon Sep 17 00:00:00 2001
From: Marshall Clow <mclow.lists@gmail.com>
Date: Wed, 7 Feb 2018 21:30:17 +0000
Subject: [PATCH] Fix PR#31454 - 'basic_string<T>::push_back() crashes if
 sizeof(T)>sizeof(long long)'. We were mishandling the small-string
 optimization calculations for very large 'characters'. This may be an ABI
 change (change the size of) strings of very large 'characters', but since
 they never worked, I'm not too concerned.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@324531 91177308-0d34-0410-b5e6-96231b3b80d8
---
 include/string                                         | 10 +++++++---
 .../string.modifiers/string_append/push_back.pass.cpp  |  3 +--
 2 files changed, 8 insertions(+), 5 deletions(-)

diff --git a/include/string b/include/string
index b213cd411..f89ef5741 100644
--- a/include/string
+++ b/include/string
@@ -1363,9 +1363,13 @@ private:
     enum {__alignment = 16};
     static _LIBCPP_INLINE_VISIBILITY
     size_type __recommend(size_type __s) _NOEXCEPT
-        {return (__s < __min_cap ? static_cast<size_type>(__min_cap) :
-                 __align_it<sizeof(value_type) < __alignment ?
-                            __alignment/sizeof(value_type) : 1 > (__s+1)) - 1;}
+        {
+        if (__s < __min_cap) return static_cast<size_type>(__min_cap) - 1;
+        size_type __guess = __align_it<sizeof(value_type) < __alignment ?
+                     __alignment/sizeof(value_type) : 1 > (__s+1) - 1;
+        if (__guess == __min_cap) ++__guess;
+        return __guess;
+        }
 
     inline
     void __init(const value_type* __s, size_type __sz, size_type __reserve);
diff --git a/test/std/strings/basic.string/string.modifiers/string_append/push_back.pass.cpp b/test/std/strings/basic.string/string.modifiers/string_append/push_back.pass.cpp
index 5ca5aaf86..128446534 100644
--- a/test/std/strings/basic.string/string.modifiers/string_append/push_back.pass.cpp
+++ b/test/std/strings/basic.string/string.modifiers/string_append/push_back.pass.cpp
@@ -48,7 +48,7 @@ int main()
     test(S("12345678901234567890"), 'a', S("12345678901234567890a"));
     }
 #endif
-#if 0
+
     {
 // https://bugs.llvm.org/show_bug.cgi?id=31454
     std::basic_string<veryLarge> s;
@@ -57,5 +57,4 @@ int main()
     s.push_back(vl);
     s.push_back(vl);
     }
-#endif
 }