[PATCH v5] tree-optimization/101186 - extend FRE with "equivalence map" for condition prediction

[Di Zhao OS via Gcc-patches]

Hi, attached is a new version of the patch. The changes are:
- Skip using temporary equivalences for floating-point values, because
folding expressions can generate incorrect values. For example, 
operations on 0.0 and -0.0 may have different results.
- Avoid inserting duplicated back-refs from value-number to predicates.
- Disable fre in testsuite/g++.dg/pr83541.C .

Summary of the previous versions:
https://gcc.gnu.org/pipermail/gcc-patches/2021-December/587346.html

Is the patch still considered?

Thanks,
Di Zhao

---

Extend FRE with temporary equivalences.

2022-05-29  Di Zhao  <diz...@os.amperecomputing.com>

gcc/ChangeLog:
        PR tree-optimization/101186
        * tree-ssa-sccvn.c (VN_INFO): remove assertions (there could be a
        predicate already).
        (dominated_by_p_w_unex): Moved upward.
        (vn_nary_op_get_predicated_value): Moved upward.
        (is_vn_valid_at_bb): Check if vn_pval is valid at BB.
        (lookup_equiv_head): Lookup the "equivalence head" of given node.
        (lookup_equiv_heads): Lookup the "equivalence head"s of given nodes.
        (vn_tracking_edge): Extracted utility function.
        (init_vn_nary_op_from_stmt): Insert and lookup by "equivalence head"s.
        (vn_nary_op_insert_into): Insert new value at the front.
        (vn_nary_op_insert_pieces_predicated_1): Insert as predicated values
        from pieces.
        (fold_const_from_equiv_heads): Fold N-ary expression of equiv-heads.
        (push_new_nary_ref): Insert a back-reference to vn_nary_op_t.
        (val_equiv_insert): Record temporary equivalence.
        (vn_nary_op_insert_pieces_predicated): Record equivalences instead of
        some predicates; insert back-refs.
        (record_equiv_from_prev_phi_1): Record temporary equivalences generated
        by PHI nodes.
        (record_equiv_from_prev_phi): Given an outgoing edge of a conditional
        expression taken, record equivalences generated by PHI nodes.
        (visit_nary_op): Add lookup previous results of N-ary operations by
        equivalences.
        (insert_related_predicates_on_edge): Some predicates can be computed
        from equivalences, no need to insert them.
        (process_bb): Add lookup predicated values by equivalences.
        (struct unwind_state): Unwind state of back-refs to vn_nary_op_t.
        (do_unwind): Unwind the back-refs to vn_nary_op_t.
        (do_rpo_vn): Update back-reference unwind state.
        * tree-ssa-sccvn.h (struct nary_ref): hold a lists of references to the
        nary map entries.

gcc/testsuite/ChangeLog:

        * g++.dg/pr83541.C: Disable fre.
        * gcc.dg/tree-ssa/pr68619-2.c: Disable fre.
        * gcc.dg/tree-ssa/pr71947-1.c: Disable fre.
        * gcc.dg/tree-ssa/pr71947-2.c: Disable fre.
        * gcc.dg/tree-ssa/pr71947-3.c: Disable fre.
        * gcc.dg/tree-ssa/pr71947-5.c: Disable fre.
        * gcc.dg/tree-ssa/pr71947-7.c: Disable fre.
        * gcc.dg/tree-ssa/pr71947-8.c: Disable fre.
        * gcc.dg/tree-ssa/pr71947-9.c: Disable fre.
        * gcc.dg/tree-ssa/vrp03.c: Disable fre.
        * gcc.dg/tree-ssa/ssa-fre-100.c: New test.
        * gcc.dg/tree-ssa/ssa-fre-101.c: New test.
        * gcc.dg/tree-ssa/ssa-fre-102.c: New test.
        * gcc.dg/tree-ssa/ssa-pre-34.c: New test.

v5-tree-optimization-101186.patch
Description: v5-tree-optimization-101186.patch