[PATCH] Fix PR91221

[Richard Biener]

Bootstrapped / tested on x86_64-unknown-linux-gnu, applied.

Richard.

2019-07-22  Richard Biener  <rguent...@suse.de>

        PR tree-optimization/91221
        * tree-ssa-sccvn.c (vn_reference_lookup_3): Appropriately
        restrict partial-def handling of empty constructors and
        memset to refs with known offset.

        * g++.dg/pr91221.C: New testcase.

Index: gcc/tree-ssa-sccvn.c
===================================================================
--- gcc/tree-ssa-sccvn.c        (revision 273657)
+++ gcc/tree-ssa-sccvn.c        (working copy)
@@ -2455,7 +2507,8 @@ vn_reference_lookup_3 (ao_ref *ref, tree
                   (vuse, vr->set, vr->type, vr->operands, val);
        }
       /* For now handle clearing memory with partial defs.  */
-      else if (integer_zerop (gimple_call_arg (def_stmt, 1))
+      else if (known_eq (ref->size, maxsize)
+              && integer_zerop (gimple_call_arg (def_stmt, 1))
               && tree_to_poly_int64 (len).is_constant (&leni)
               && offset.is_constant (&offseti)
               && offset2.is_constant (&offset2i)
@@ -2503,7 +2556,8 @@ vn_reference_lookup_3 (ao_ref *ref, tree
              return vn_reference_lookup_or_insert_for_pieces
                  (vuse, vr->set, vr->type, vr->operands, val);
            }
-         else if (maxsize.is_constant (&maxsizei)
+         else if (known_eq (ref->size, maxsize)
+                  && maxsize.is_constant (&maxsizei)
                   && maxsizei % BITS_PER_UNIT == 0
                   && offset.is_constant (&offseti)
                   && offseti % BITS_PER_UNIT == 0
Index: gcc/testsuite/g++.dg/pr91221.C
===================================================================
--- gcc/testsuite/g++.dg/pr91221.C      (nonexistent)
+++ gcc/testsuite/g++.dg/pr91221.C      (working copy)
@@ -0,0 +1,13 @@
+// { dg-do compile }
+// { dg-options "-O2 -fno-ipa-pure-const -fpack-struct 
-Wno-address-of-packed-member" }
+
+void printf(...);
+struct A {
+    A() : bar_(), dbar_() {
+       for (int i;; i++)
+         printf(i, bar_[i]);
+    }
+    int bar_[5];
+    double dbar_[5];
+};
+void fn1() { A a; }