re PR rtl-optimization/16380 (Use of uninitialised register after dbra conversion)

	PR rtl-optimization/16380
	* loop.c (check_dbra_loop): Sink comparison instructions if they
	do something other than set cc0.

From-SVN: r84161

gcc/ChangeLog

+2004-07-06  Richard Sandiford  <rsandifo@redhat.com>
+
+	PR rtl-optimization/16380
+	* loop.c (check_dbra_loop): Sink comparison instructions if they
+	do something other than set cc0.
+
 2004-07-06  James E Wilson  <wilson@specifixinc.com>
 
 	* doc/interface.texi (longjmp and automatic variables): Delete

gcc/loop.c

@@ -8284,6 +8284,7 @@ check_dbra_loop (struct loop *loop, int insn_count)
 	      enum rtx_code cmp_code;
 	      int comparison_const_width;
 	      unsigned HOST_WIDE_INT comparison_sign_mask;
+	      bool keep_first_compare;
 
 	      add_val = INTVAL (bl->biv->add_val);
 	      comparison_value = XEXP (comparison, 1);
@@ -8476,13 +8477,26 @@ check_dbra_loop (struct loop *loop, int insn_count)
 		 not delete the label.  */
 	      LABEL_NUSES (XEXP (jump_label, 0))++;
 
+	      /* If we have a separate comparison insn that does more
+		 than just set cc0, the result of the comparison might
+		 be used outside the loop.  */
+	      keep_first_compare = (compare_and_branch == 2
+#ifdef HAVE_CC0
+				    && sets_cc0_p (first_compare) <= 0
+#endif
+				    );
+
 	      /* Emit an insn after the end of the loop to set the biv's
 		 proper exit value if it is used anywhere outside the loop.  */
-	      if ((REGNO_LAST_UID (bl->regno) != INSN_UID (first_compare))
+	      if (keep_first_compare
+		  || (REGNO_LAST_UID (bl->regno) != INSN_UID (first_compare))
 		  || ! bl->init_insn
 		  || REGNO_FIRST_UID (bl->regno) != INSN_UID (bl->init_insn))
 		loop_insn_sink (loop, gen_load_of_final_value (reg, final_value));
 
+	      if (keep_first_compare)
+		loop_insn_sink (loop, PATTERN (first_compare));
+
 	      /* Delete compare/branch at end of loop.  */
 	      delete_related_insns (PREV_INSN (loop_end));
 	      if (compare_and_branch == 2)

gcc/testsuite/ChangeLog

+2004-07-06  Richard Sandiford  <rsandifo@redhat.com>
+
+	* gcc.c-torture/execute/20040706-1.c: New test.
+
 2004-07-06  Giovanni Bajo  <giovannibajo@gcc.gnu.org>
 
 	PR c++/3671

gcc/testsuite/gcc.c-torture/execute/20040706-1.c

+int main ()
+{
+  int i;
+  for (i = 0; i < 10; i++)
+    continue;
+  if (i < 10)
+    abort ();
+  exit (0);
+}