[Bug tree-optimization/105329] [12/13 Regression] Bogus restrict warning when assigning 1-char string literal to std::string since r12-3347-g8af8abfbbace49e6

[jakub at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105329

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jakub at gcc dot gnu.org

--- Comment #14 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Here is an untested patch for the cold part of the function:
--- libstdc++-v3/include/bits/basic_string.h.jj 2022-01-21 22:48:42.220261654
+0100
+++ libstdc++-v3/include/bits/basic_string.h    2022-05-02 15:51:42.381923962
+0200
@@ -2504,6 +2504,10 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
       _M_replace_aux(size_type __pos1, size_type __n1, size_type __n2,
                     _CharT __c);

+      __attribute__((__noinline__, __noclone__, __cold__)) void
+      _M_replace_cold(pointer __p, size_type __len1, const _CharT* __s,
+                     const size_type __len2, const size_type __how_much);
+
       _GLIBCXX20_CONSTEXPR
       basic_string&
       _M_replace(size_type __pos, size_type __len1, const _CharT* __s,
--- libstdc++-v3/include/bits/basic_string.tcc.jj       2022-01-11
22:31:41.482757256 +0100
+++ libstdc++-v3/include/bits/basic_string.tcc  2022-05-02 15:51:38.630975348
+0200
@@ -471,6 +471,37 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     }

   template<typename _CharT, typename _Traits, typename _Alloc>
+    __attribute__((__noinline__, __noclone__, __cold__)) void
+    basic_string<_CharT, _Traits, _Alloc>::
+    _M_replace_cold(pointer __p, size_type __len1, const _CharT* __s,
+                   const size_type __len2, const size_type __how_much)
+    {
+      // Work in-place.
+      if (__len2 && __len2 <= __len1)
+       this->_S_move(__p, __s, __len2);
+      if (__how_much && __len1 != __len2)
+       this->_S_move(__p + __len2, __p + __len1, __how_much);
+      if (__len2 > __len1)
+       {
+         if (__s + __len2 <= __p + __len1)
+           this->_S_move(__p, __s, __len2);
+         else if (__s >= __p + __len1)
+           {
+             // Hint to middle end that __p and __s overlap
+             // (PR 98465).
+             const size_type __poff = (__s - __p) + (__len2 - __len1);
+             this->_S_copy(__p, __p + __poff, __len2);
+           }
+         else
+           {
+             const size_type __nleft = (__p + __len1) - __s;
+             this->_S_move(__p, __s, __nleft);
+             this->_S_copy(__p + __nleft, __p + __len2, __len2 - __nleft);
+           }
+       }
+    }
+
+  template<typename _CharT, typename _Traits, typename _Alloc>
     _GLIBCXX20_CONSTEXPR
     basic_string<_CharT, _Traits, _Alloc>&
     basic_string<_CharT, _Traits, _Alloc>::
@@ -500,7 +531,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
            }
          else
 #endif
-         if (_M_disjunct(__s))
+         if (__builtin_expect(_M_disjunct(__s),true))
            {
              if (__how_much && __len1 != __len2)
                this->_S_move(__p + __len2, __p + __len1, __how_much);
@@ -508,32 +539,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
                this->_S_copy(__p, __s, __len2);
            }
          else
-           {
-             // Work in-place.
-             if (__len2 && __len2 <= __len1)
-               this->_S_move(__p, __s, __len2);
-             if (__how_much && __len1 != __len2)
-               this->_S_move(__p + __len2, __p + __len1, __how_much);
-             if (__len2 > __len1)
-               {
-                 if (__s + __len2 <= __p + __len1)
-                   this->_S_move(__p, __s, __len2);
-                 else if (__s >= __p + __len1)
-                   {
-                     // Hint to middle end that __p and __s overlap
-                     // (PR 98465).
-                     const size_type __poff = (__s - __p) + (__len2 - __len1);
-                     this->_S_copy(__p, __p + __poff, __len2);
-                   }
-                 else
-                   {
-                     const size_type __nleft = (__p + __len1) - __s;
-                     this->_S_move(__p, __s, __nleft);
-                     this->_S_copy(__p + __nleft, __p + __len2,
-                                   __len2 - __nleft);
-                   }
-               }
-           }
+           _M_replace_cold(__p, __len1, __s, __len2, __how_much);
        }
       else
        this->_M_mutate(__pos, __len1, __s, __len2);
Note, on the #c0 testcase alone it actually results in larger generated code
(unless we arrange for it to be exported from libstdc++, for which it is quite
late for 12.1 right now), but say on:
#include <string>

void f (std::string& s)
{
  s = "5";
}

void g (std::string& s)
{
  s = "56";
}

void h (std::string& s)
{
  s = "6";
}
it is already smaller (note, obviously it doesn't need to be in the same TU).