commit e9a55125f1368668bef3b8073bb6fa37f789c1f6
author Arthur O'Dwyer <arthur.j.odwyer@gmail.com> Tue Apr 20 22:24:24 2021 -0400
committer Copybara-Service <copybara-worker@google.com> Mon Sep 20 11:50:57 2021 -0700
tree 6535b776b54ef87123479b64933054ce3761de92
parent 7bcb38529dbe11a74c5eb946e0adfe8ed497e1b9

[libc++] [LIBCXX-DEBUG-FIXME] Constexpr char_traits::copy mustn't compare unrelated pointers.

Now that __builtin_is_constant_evaluated() is present on all supported
compilers, we can use it to skip the UB-inducing assert in cases where
the computation might be happening at constexpr time.

Differential Revision: https://reviews.llvm.org/D101674

NOKEYCHECK=True
GitOrigin-RevId: df81bb71aa452c677984fbeb7c34e8a77ec3e83b

include/__string

diff --git a/include/__string b/include/__string
index a23e7c9..a968fc0 100644
--- a/include/__string
+++ b/include/__string
@@ -265,7 +265,9 @@
 _CharT*
 char_traits<_CharT>::copy(char_type* __s1, const char_type* __s2, size_t __n)
 {
-    _LIBCPP_ASSERT(__s2 < __s1 || __s2 >= __s1+__n, "char_traits::copy overlapped range");
+    if (!__libcpp_is_constant_evaluated()) {
+        _LIBCPP_ASSERT(__s2 < __s1 || __s2 >= __s1+__n, "char_traits::copy overlapped range");
+    }
     char_type* __r = __s1;
     for (; __n; --__n, ++__s1, ++__s2)
         assign(*__s1, *__s2);
@@ -348,7 +350,9 @@
     static inline _LIBCPP_CONSTEXPR_AFTER_CXX17
     char_type* copy(char_type* __s1, const char_type* __s2, size_t __n) _NOEXCEPT
         {
-            _LIBCPP_ASSERT(__s2 < __s1 || __s2 >= __s1+__n, "char_traits::copy overlapped range");
+            if (!__libcpp_is_constant_evaluated()) {
+                _LIBCPP_ASSERT(__s2 < __s1 || __s2 >= __s1+__n, "char_traits::copy overlapped range");
+            }
             return __libcpp_is_constant_evaluated()
                        ? _VSTD::__copy_constexpr(__s1, __s2, __n)
                        : __n == 0 ? __s1 : (char_type*)_VSTD::memcpy(__s1, __s2, __n);
@@ -451,7 +455,9 @@
     static inline _LIBCPP_CONSTEXPR_AFTER_CXX17
     char_type* copy(char_type* __s1, const char_type* __s2, size_t __n) _NOEXCEPT
         {
-            _LIBCPP_ASSERT(__s2 < __s1 || __s2 >= __s1+__n, "char_traits::copy overlapped range");
+            if (!__libcpp_is_constant_evaluated()) {
+                _LIBCPP_ASSERT(__s2 < __s1 || __s2 >= __s1+__n, "char_traits::copy overlapped range");
+            }
             return __libcpp_is_constant_evaluated()
                        ? _VSTD::__copy_constexpr(__s1, __s2, __n)
                        : __n == 0 ? __s1 : _VSTD::wmemcpy(__s1, __s2, __n);
@@ -582,8 +588,10 @@
 
     static _LIBCPP_CONSTEXPR_AFTER_CXX17
     char_type*       copy(char_type* __s1, const char_type* __s2, size_t __n) _NOEXCEPT
-       {
-            _LIBCPP_ASSERT(__s2 < __s1 || __s2 >= __s1+__n, "char_traits::copy overlapped range");
+        {
+            if (!__libcpp_is_constant_evaluated()) {
+                _LIBCPP_ASSERT(__s2 < __s1 || __s2 >= __s1+__n, "char_traits::copy overlapped range");
+            }
             return __libcpp_is_constant_evaluated()
                        ? _VSTD::__copy_constexpr(__s1, __s2, __n)
                        : __n == 0 ? __s1 : (char_type*)_VSTD::memcpy(__s1, __s2, __n);
@@ -759,7 +767,9 @@
 char16_t*
 char_traits<char16_t>::copy(char_type* __s1, const char_type* __s2, size_t __n) _NOEXCEPT
 {
-    _LIBCPP_ASSERT(__s2 < __s1 || __s2 >= __s1+__n, "char_traits::copy overlapped range");
+    if (!__libcpp_is_constant_evaluated()) {
+        _LIBCPP_ASSERT(__s2 < __s1 || __s2 >= __s1+__n, "char_traits::copy overlapped range");
+    }
     char_type* __r = __s1;
     for (; __n; --__n, ++__s1, ++__s2)
         assign(*__s1, *__s2);
@@ -879,7 +889,9 @@
 char32_t*
 char_traits<char32_t>::copy(char_type* __s1, const char_type* __s2, size_t __n) _NOEXCEPT
 {
-    _LIBCPP_ASSERT(__s2 < __s1 || __s2 >= __s1+__n, "char_traits::copy overlapped range");
+    if (!__libcpp_is_constant_evaluated()) {
+        _LIBCPP_ASSERT(__s2 < __s1 || __s2 >= __s1+__n, "char_traits::copy overlapped range");
+    }
     char_type* __r = __s1;
     for (; __n; --__n, ++__s1, ++__s2)
         assign(*__s1, *__s2);