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; }