re PR libstdc++/80721 (Sorting/Merging of free EH-emergency buffer may wrong or uncomplete)

2017-06-02  Richard Biener  <rguenther@suse.de>
	Markus Eisenmann  <meisenmann.lba@fh-salzburg.ac.at>

	PR libstdc++/80721
	* libsupc++/eh_alloc.cc (pool::free): Keep list properly
	sorted and add missing freelist item merging cases.

Co-Authored-By: Markus Eisenmann <meisenmann.lba@fh-salzburg.ac.at>

From-SVN: r248816

libstdc++-v3/ChangeLog

+2017-06-02  Richard Biener  <rguenther@suse.de>
+	Markus Eisenmann  <meisenmann.lba@fh-salzburg.ac.at>
+
+	PR libstdc++/80721
+	* libsupc++/eh_alloc.cc (pool::free): Keep list properly
+	sorted and add missing freelist item merging cases.
+
 2017-06-01  Rainer Orth  <ro@CeBiTec.Uni-Bielefeld.DE>
 
 	(GLIBCXX_CROSSCONFIG): Handle *-solaris* like *-linux* etc.

libstdc++-v3/libsupc++/eh_alloc.cc

@@ -162,7 +162,7 @@ namespace
       allocated_entry *x;
       if ((*e)->size - size >= sizeof (free_entry))
 	{
-	  // Slit block if it is too large.
+	  // Split block if it is too large.
 	  free_entry *f = reinterpret_cast <free_entry *>
 	      (reinterpret_cast <char *> (*e) + size);
 	  std::size_t sz = (*e)->size;
@@ -194,13 +194,17 @@ namespace
       allocated_entry *e = reinterpret_cast <allocated_entry *>
 	(reinterpret_cast <char *> (data) - offsetof (allocated_entry, data));
       std::size_t sz = e->size;
-      if (!first_free_entry)
+      if (!first_free_entry
+	  || (reinterpret_cast <char *> (e) + sz
+	      < reinterpret_cast <char *> (first_free_entry)))
 	{
-	  // If the free list is empty just put the entry there.
+	  // If the free list is empty or the entry is before the
+	  // first element and cannot be merged with it add it as
+	  // the first free entry.
 	  free_entry *f = reinterpret_cast <free_entry *> (e);
 	  new (f) free_entry;
 	  f->size = sz;
-	  f->next = NULL;
+	  f->next = first_free_entry;
 	  first_free_entry = f;
 	}
       else if (reinterpret_cast <char *> (e) + sz
@@ -224,9 +228,17 @@ namespace
 		   > reinterpret_cast <char *> (e) + sz);
 	       fe = &(*fe)->next)
 	    ;
+	  // If we can merge the next block into us do so and continue
+	  // with the cases below.
+	  if (reinterpret_cast <char *> (e) + sz
+	      == reinterpret_cast <char *> ((*fe)->next))
+	    {
+	      sz += (*fe)->next->size;
+	      (*fe)->next = (*fe)->next->next;
+	    }
 	  if (reinterpret_cast <char *> (*fe) + (*fe)->size
 	      == reinterpret_cast <char *> (e))
-	    /* Merge with the freelist entry.  */
+	    // Merge with the freelist entry.
 	    (*fe)->size += sz;
 	  else
 	    {