diff options
| author | Richard Biener <rguenther@suse.de> | 2019-12-03 10:46:52 +0000 |
|---|---|---|
| committer | Richard Biener <rguenth@gcc.gnu.org> | 2019-12-03 10:46:52 +0000 |
| commit | 89ee3a872fdf460402d1fc137e5cdce20f62bc8e (patch) | |
| tree | df1eaf56a9937444db526351efb2b1ab571fc9b6 /gcc/tree-ssa-sccvn.c | |
| parent | 1058a2262b9dc15c164dec5261a9b3daad84e6d6 (diff) | |
re PR tree-optimization/92751 (VN partial def support confused about clobbers)
2019-12-03 Richard Biener <rguenther@suse.de>
PR tree-optimization/92751
* tree-ssa-sccvn.c (vn_walk_cb_data::push_partial_def): Fail
when a clobber ends up in the partial-def vector.
(vn_reference_lookup_3): Let clobbers be handled by the
assignment from CTOR handling.
* g++.dg/tree-ssa/pr92751.C: New testcase.
From-SVN: r278931
Diffstat (limited to 'gcc/tree-ssa-sccvn.c')
| -rw-r--r-- | gcc/tree-ssa-sccvn.c | 20 |
1 files changed, 15 insertions, 5 deletions
diff --git a/gcc/tree-ssa-sccvn.c b/gcc/tree-ssa-sccvn.c index 8a7e0475ff8..8fbdb5163d6 100644 --- a/gcc/tree-ssa-sccvn.c +++ b/gcc/tree-ssa-sccvn.c @@ -1761,6 +1761,9 @@ vn_walk_cb_data::push_partial_def (const pd_data &pd, tree vuse, if (partial_defs.is_empty ()) { + /* If we get a clobber upfront, fail. */ + if (TREE_CLOBBER_P (pd.rhs)) + return (void *)-1; partial_defs.safe_push (pd); first_range.offset = pd.offset; first_range.size = pd.size; @@ -1792,7 +1795,8 @@ vn_walk_cb_data::push_partial_def (const pd_data &pd, tree vuse, && ranges_known_overlap_p (r->offset, r->size + 1, newr.offset, newr.size)) { - /* Ignore partial defs already covered. */ + /* Ignore partial defs already covered. Here we also drop shadowed + clobbers arriving here at the floor. */ if (known_subrange_p (newr.offset, newr.size, r->offset, r->size)) return NULL; r->size = MAX (r->offset + r->size, newr.offset + newr.size) - r->offset; @@ -1817,6 +1821,9 @@ vn_walk_cb_data::push_partial_def (const pd_data &pd, tree vuse, rafter->offset + rafter->size) - r->offset; splay_tree_remove (known_ranges, (splay_tree_key)&rafter->offset); } + /* If we get a clobber, fail. */ + if (TREE_CLOBBER_P (pd.rhs)) + return (void *)-1; partial_defs.safe_push (pd); /* Now we have merged newr into the range tree. When we have covered @@ -2355,10 +2362,6 @@ vn_reference_lookup_3 (ao_ref *ref, tree vuse, void *data_, poly_int64 offset = ref->offset; poly_int64 maxsize = ref->max_size; - /* We can't deduce anything useful from clobbers. */ - if (gimple_clobber_p (def_stmt)) - return (void *)-1; - /* def_stmt may-defs *ref. See if we can derive a value for *ref from that definition. 1) Memset. */ @@ -2508,6 +2511,10 @@ vn_reference_lookup_3 (ao_ref *ref, tree vuse, void *data_, if (data->partial_defs.is_empty () && known_subrange_p (offset, maxsize, offset2, size2)) { + /* While technically undefined behavior do not optimize + a full read from a clobber. */ + if (gimple_clobber_p (def_stmt)) + return (void *)-1; tree val = build_zero_cst (vr->type); return vn_reference_lookup_or_insert_for_pieces (vuse, get_alias_set (lhs), vr->type, vr->operands, val); @@ -2522,6 +2529,9 @@ vn_reference_lookup_3 (ao_ref *ref, tree vuse, void *data_, && size2.is_constant (&size2i) && size2i % BITS_PER_UNIT == 0) { + /* Let clobbers be consumed by the partial-def tracker + which can choose to ignore them if they are shadowed + by a later def. */ pd_data pd; pd.rhs = gimple_assign_rhs1 (def_stmt); pd.offset = (offset2i - offseti) / BITS_PER_UNIT; |