[gcc r11-4887] libstdc++: Fix more unspecified comparisons to null pointer [PR 97415]

[Jonathan Wakely]

https://gcc.gnu.org/g:ced70ebaa372945ec8d73703d81e4a10d6d51c9b

commit r11-4887-gced70ebaa372945ec8d73703d81e4a10d6d51c9b
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Tue Nov 10 15:46:02 2020 +0000

    libstdc++: Fix more unspecified comparisons to null pointer [PR 97415]
    
    This adds some more null checks to avoid a relational comparison with a
    null pointer, similar to 78198b6021a9695054dab039340202170b88423c.
    
    libstdc++-v3/ChangeLog:
    
            PR libstdc++/97415
            * include/std/sstream (basic_stringbuf::_M_update_egptr)
            (basic_stringbuf::__xfer_bufptrs::__xfer_bufptrs): Check for
            null before comparing pointers.

Diff:
---
 libstdc++-v3/include/std/sstream | 17 ++++++++++-------
 1 file changed, 10 insertions(+), 7 deletions(-)

diff --git a/libstdc++-v3/include/std/sstream b/libstdc++-v3/include/std/sstream
index 437e2ba2a5f..9c50e4e8328 100644
--- a/libstdc++-v3/include/std/sstream
+++ b/libstdc++-v3/include/std/sstream
@@ -357,13 +357,16 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
       void
       _M_update_egptr()
       {
-	const bool __testin = _M_mode & ios_base::in;
-	if (this->pptr() && this->pptr() > this->egptr())
+	if (char_type* __pptr = this->pptr())
 	  {
-	    if (__testin)
-	      this->setg(this->eback(), this->gptr(), this->pptr());
-	    else
-	      this->setg(this->pptr(), this->pptr(), this->pptr());
+	    char_type* __egptr = this->egptr();
+	    if (!__egptr || __pptr > __egptr)
+	      {
+		if (_M_mode & ios_base::in)
+		  this->setg(this->eback(), this->gptr(), __pptr);
+		else
+		  this->setg(__pptr, __pptr, __pptr);
+	      }
 	  }
       }
 
@@ -396,7 +399,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
 	      _M_poff[0] = __from.pbase() - __str;
 	      _M_poff[1] = __from.pptr() - __from.pbase();
 	      _M_poff[2] = __from.epptr() - __str;
-	      if (__from.pptr() > __end)
+	      if (!__end || __from.pptr() > __end)
 		__end = __from.pptr();
 	    }