The following fixes bogus redundant store removal by FRE/PRE and bogus "store match" detections by VN. This amends the similar PR69776 fix.
Bootstraped on x86_64-unknown-linux-gnu, testing in progress. 2016-09-27 Richard Biener <rguent...@suse.de> PR tree-optimization/77745 * tree-ssa-pre.c (eliminate_dom_walker::before_dom_children): When removing redundant stores make sure to check compatibility of the TBAA state for downstream accesses. * tree-ssa-sccvn.c (visit_reference_op_store): Likewise for when value-numbering virtual operands for store matches. * g++.dg/torture/pr77745.C: New testcase. Index: gcc/tree-ssa-pre.c =================================================================== --- gcc/tree-ssa-pre.c (revision 240521) +++ gcc/tree-ssa-pre.c (working copy) @@ -4431,26 +4436,34 @@ eliminate_dom_walker::before_dom_childre && !is_gimple_reg (gimple_assign_lhs (stmt)) && (TREE_CODE (gimple_assign_rhs1 (stmt)) == SSA_NAME || is_gimple_min_invariant (gimple_assign_rhs1 (stmt)))) - { - tree val; + { + tree val; tree rhs = gimple_assign_rhs1 (stmt); - val = vn_reference_lookup (gimple_assign_lhs (stmt), - gimple_vuse (stmt), VN_WALK, NULL, false); - if (TREE_CODE (rhs) == SSA_NAME) - rhs = VN_INFO (rhs)->valnum; - if (val - && operand_equal_p (val, rhs, 0)) - { - if (dump_file && (dump_flags & TDF_DETAILS)) - { - fprintf (dump_file, "Deleted redundant store "); - print_gimple_stmt (dump_file, stmt, 0, 0); - } + vn_reference_t vnresult; + val = vn_reference_lookup (lhs, gimple_vuse (stmt), VN_WALKREWRITE, + &vnresult, false); + if (TREE_CODE (rhs) == SSA_NAME) + rhs = VN_INFO (rhs)->valnum; + if (val + && operand_equal_p (val, rhs, 0)) + { + /* We can only remove the later store if the former aliases + at least all accesses the later one does. */ + alias_set_type set = get_alias_set (lhs); + if (vnresult->set == set + || alias_set_subset_of (set, vnresult->set)) + { + if (dump_file && (dump_flags & TDF_DETAILS)) + { + fprintf (dump_file, "Deleted redundant store "); + print_gimple_stmt (dump_file, stmt, 0, 0); + } - /* Queue stmt for removal. */ - el_to_remove.safe_push (stmt); - continue; - } + /* Queue stmt for removal. */ + el_to_remove.safe_push (stmt); + continue; + } + } } /* If this is a control statement value numbering left edges Index: gcc/tree-ssa-sccvn.c =================================================================== --- gcc/tree-ssa-sccvn.c (revision 240521) +++ gcc/tree-ssa-sccvn.c (working copy) @@ -3599,13 +3706,21 @@ visit_reference_op_store (tree lhs, tree Otherwise, the vdefs for the store are used when inserting into the table, since the store generates a new memory state. */ - result = vn_reference_lookup (lhs, vuse, VN_NOWALK, NULL, false); - + result = vn_reference_lookup (lhs, vuse, VN_NOWALK, &vnresult, false); if (result) { if (TREE_CODE (result) == SSA_NAME) result = SSA_VAL (result); resultsame = expressions_equal_p (result, op); + if (resultsame) + { + /* If the TBAA state isn't compatible for downstream reads + we cannot value-number the VDEFs the same. */ + alias_set_type set = get_alias_set (lhs); + if (vnresult->set != set + && ! alias_set_subset_of (set, vnresult->set)) + resultsame = false; + } } if ((!result || !resultsame) Index: gcc/testsuite/g++.dg/torture/pr77745.C =================================================================== --- gcc/testsuite/g++.dg/torture/pr77745.C (revision 0) +++ gcc/testsuite/g++.dg/torture/pr77745.C (working copy) @@ -0,0 +1,24 @@ +// { dg-do run } + +inline void* operator new(__SIZE_TYPE__, void* __p) noexcept { return __p; } + +long foo(char *c1, char *c2) +{ + long *p1 = new (c1) long; + *p1 = 100; + long long *p2 = new (c2) long long; + *p2 = 200; + long *p3 = new (c2) long; + *p3 = 200; + return *p1; +} +int main() +{ + union { + char c; + long l; + long long ll; + } c; + if (foo(&c.c, &c.c) != 200) + __builtin_abort(); +}