re PR rtl-optimization/6713 (Regression wrt 3.0.4: g++ -O2 leads to seg fault at run time)

 PR optimization/6713
 * loop.c (loop_givs_rescan): Explicitly delete the insn that
 sets a non-replaceable giv after issuing the new one.

Co-Authored-By: Glen Nakamura <glen@imodulo.com>

From-SVN: r55539

gcc/ChangeLog

+2002-06-17  Eric Botcazou <ebotcazou@multimania.com>
+            Glen Nakamura <glen@imodulo.com>
+
+	PR optimization/6713
+	* loop.c (loop_givs_rescan): Explicitly delete the insn that
+	sets a non-replaceable giv after issuing the new one.
+
 2002-07-17  Neil Booth  <neil@daikokuya.co.uk>
 
 	* cppexp.c (cpp_interpret_integer, append_digit, parse_defined,

gcc/loop.c

@@ -4874,10 +4874,20 @@ loop_givs_rescan (loop, bl, reg_map)
 	}
       else
 	{
+	  rtx original_insn = v->insn;
+
 	  /* Not replaceable; emit an insn to set the original giv reg from
 	     the reduced giv, same as above.  */
-	  loop_insn_emit_after (loop, 0, v->insn,
-				gen_move_insn (v->dest_reg, v->new_reg));
+	  v->insn = loop_insn_emit_after (loop, 0, original_insn,
+					  gen_move_insn (v->dest_reg,
+							 v->new_reg));
+
+	  /* The original insn may have a REG_EQUAL note.  This note is
+	     now incorrect and may result in invalid substitutions later.
+	     We could just delete the note, but we know that the entire
+	     insn is dead, so we might as well save ourselves the bother
+	     and remove the whole thing.  */
+	  delete_insn (original_insn);
 	}
 
       /* When a loop is reversed, givs which depend on the reversed

gcc/testsuite/g++.dg/opt/pr6713.C

+// PR optimization/6713
+// This testcase segfaulted on x86 because a dangling REG_EQUAL note
+// resulted in incorrect substitutions later.
+// { dg-do run }
+// { dg-options "-O2" }
+
+template<typename _CharT> class basic_iterator
+{
+  public:
+    basic_iterator(_CharT* _p) : _M_current(_p) {}
+    basic_iterator& operator++() { ++_M_current; return *this; }
+    _CharT& operator*() const { return *_M_current; }
+    bool operator!=(basic_iterator &_rhs) { return _M_current != _rhs._M_current; }
+
+  private:
+    _CharT* _M_current;
+};
+
+template<typename _CharT> class basic_string
+{
+  public:
+    typedef unsigned int size_type;
+    typedef basic_iterator<_CharT> iterator;
+
+  private:
+    struct _Rep
+    {
+      size_type _M_length;
+      size_type _M_capacity;
+      int _M_references;
+
+      bool _M_is_leaked() const { return _M_references < 0; }
+      bool _M_is_shared() const { return _M_references > 0; }
+      void _M_set_leaked() { _M_references = -1; }
+      void _M_set_sharable() { _M_references = 0; }
+    };
+
+    struct _Rep _M_rep;
+
+    struct _Alloc_hider
+    {
+      _CharT _raw[16];
+      _CharT* _M_p;
+    };
+
+    mutable _Alloc_hider _M_dataplus;
+
+    _CharT* _M_data() const { return _M_dataplus._M_p; }
+
+    void _M_leak() { if (!_M_rep._M_is_leaked()) _M_leak_hard(); }
+
+    static int count;
+
+    static void _M_leak_hard();
+
+  public:
+    explicit basic_string(const _CharT* __s);
+
+    iterator begin() { _M_leak(); return iterator(_M_data()); }
+
+    iterator end() { _M_leak(); return iterator(_M_data() + this->size()); }
+
+    size_type size() const { return _M_rep._M_length; }
+};
+
+template<typename _CharT> basic_string<_CharT>::
+basic_string(const _CharT* __s)
+{
+  int i;
+
+  for (i=0; i<15; i++) {
+    if (!__s[i])
+      break;
+
+    _M_dataplus._raw[i] = __s[i];
+  }
+
+  _M_dataplus._raw[i] = 0;
+  _M_dataplus._M_p = _M_dataplus._raw;
+
+  _M_rep._M_length = i;
+  _M_rep._M_capacity = i;
+  _M_rep._M_references = 1;
+}     
+
+template<typename _CharT> int basic_string<_CharT>::count = 0;
+
+template<typename _CharT> void basic_string<_CharT>::
+_M_leak_hard()
+{
+  count++;
+}
+
+typedef basic_string<char> string;
+
+
+int isspa(int ch)
+{
+  return 0;
+}
+
+void foo(string& str)
+{
+  string::iterator it = str.begin();
+  string::iterator stop = str.end();
+
+  for (; it != stop; ++it)
+    if (isspa(*it))
+      break;
+}
+
+int main()
+{
+  string str("test");
+  foo(str);
+}