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

1 files changed, 5 insertions, 1 deletions

diff --git a/gcc/web.c b/gcc/web.c
index 9b84924..7014aa5 100644
--- a/gcc/web.c
+++ b/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));