Fix handling of stores in modref_summary::useful_p

[Jan Hubicka]

Hi,
this patch fixes a pasto in modref_summary::useful_p that made
ipa-modref to give up on tracking stores when all load info got lost.

Bootstrapped/regtested x86_64-linux, comitted.

gcc/ChangeLog:

2020-09-27  Jan Hubicka  <hubicka@ucw.cz>

	* ipa-modref.c (modref_summary::useful_p): Fix testing of stores.

diff --git a/gcc/ipa-modref.c b/gcc/ipa-modref.c
index 728c6c1523d..6225552e41a 100644
--- a/gcc/ipa-modref.c
+++ b/gcc/ipa-modref.c
@@ -135,7 +135,7 @@ modref_summary::useful_p (int ecf_flags)
     return true;
   if (ecf_flags & ECF_PURE)
     return false;
-  return stores && !loads->every_base;
+  return stores && !stores->every_base;
 }
 
 /* Dump A to OUT.  */