re PR rtl-optimization/42631 ("-fcompare-debug failure" with "-O1 -funroll-loops")

	PR debug/42631
	* web.c (entry_register): Don't clobber the number of the
	first uninitialized reference in used[].

	testsuite/
	PR debug/42631
	* gcc.dg/pr42631.c: Update test.
	* gcc.dg/pr42631-2.c: New test.

From-SVN: r169851

gcc/ChangeLog

+2011-02-05  Jie Zhang  <jie@codesourcery.com>
+
+	PR debug/42631
+	* web.c (entry_register): Don't clobber the number of the
+	first uninitialized reference in used[].
+
 2011-02-04  Sebastian Pop  <sebastian.pop@amd.com>
 
 	PR tree-optimization/46194

gcc/testsuite/ChangeLog

+2011-02-05  Jie Zhang  <jie@codesourcery.com>
+
+	PR debug/42631
+	* gcc.dg/pr42631.c: Update test.
+	* gcc.dg/pr42631-2.c: New test.
+
 2001-02-05  Thomas Koenig  <tkoenig@gcc.gnu.org>
 
 	PR fortran/47574

gcc/testsuite/gcc.dg/pr42631-2.c

+/* { dg-do compile } */
+/* { dg-options "-O2 -funroll-loops -fdump-rtl-web" } */
+
+foo()
+{
+}
+
+/* { dg-final { scan-rtl-dump-not "Web oldreg" "web" } } */
+/* { dg-final { cleanup-rtl-dump "web" } } */

gcc/testsuite/gcc.dg/pr42631.c

@@ -14,10 +14,13 @@
    combine uninitialized uses into a single web.  */
 
 /* { dg-do compile } */
-/* { dg-options "-g -O1 -funroll-loops -fcompare-debug" } */
+/* { dg-options "-g -O1 -funroll-loops -fcompare-debug -fdump-rtl-web" } */
 
 void foo()
 {
   unsigned k;
   while (--k > 0);
 }
+
+/* { dg-final { scan-rtl-dump-not "Web oldreg" "web" } } */
+/* { dg-final { cleanup-rtl-dump "web" } } */

gcc/web.c

@@ -260,7 +260,11 @@ entry_register (struct web_entry *entry, df_ref ref, unsigned int *used)
      and there won't be any use for the other values when we get to
      this point.  */
   if (used[REGNO (reg)] != 1)
-    newreg = reg, used[REGNO (reg)] = 1;
+    {
+      newreg = reg;
+      if (!used[REGNO (reg)])
+	used[REGNO (reg)] = 1;
+    }
   else
     {
       newreg = gen_reg_rtx (GET_MODE (reg));