commit 088e6015b20fd097f7b00bb330c359added2c9c5
author Marshall Clow <mclow.lists@gmail.com> Wed Feb 07 21:30:17 2018 +0000
committer Marshall Clow <mclow.lists@gmail.com> Wed Feb 07 21:30:17 2018 +0000
tree d6052dc579a489054eb56e5153034ab266a5594b
parent 2e1fa09f682befb69d4f3f13559031220250a28e

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

diff --git a/include/string b/include/string
index b213cd4..f89ef57 100644
--- a/include/string
+++ b/include/string
@@ -1363,9 +1363,13 @@
     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);

test/std/strings/basic.string/string.modifiers/string_append/push_back.pass.cpp

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 5ca5aaf..1284465 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 @@
     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 @@
     s.push_back(vl);
     s.push_back(vl);
     }
-#endif
 }