[Bug tree-optimization/98255] [10 Regression] wrong code at -Os and above with -fPIC on x86_64-pc-linux-gnu

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98255

--- Comment #17 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-10 branch has been updated by Jakub Jelinek
<jakub@gcc.gnu.org>:

https://gcc.gnu.org/g:8e28ebfa5a359942752ca9f5e774cadd1878005a

commit r10-9316-g8e28ebfa5a359942752ca9f5e774cadd1878005a
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Fri Jan 22 11:42:03 2021 +0100

    on ARRAY_REFs sign-extend offsets only from sizetype's precision [PR98255]

    As discussed in the PR, the problem here is that the routines changed in
    this patch sign extend the difference of index and low_bound from the
    precision of the index, so e.g. when index is unsigned int and contains
    value -2U, we treat it as index -2 rather than 0x00000000fffffffeU on
64-bit
    arches.
    On the other hand, get_inner_reference which is used during expansion,
does:
                if (! integer_zerop (low_bound))
                  index = fold_build2 (MINUS_EXPR, TREE_TYPE (index),
                                       index, low_bound);

                offset = size_binop (PLUS_EXPR, offset,
                                     size_binop (MULT_EXPR,
                                                 fold_convert (sizetype,
index),
                                                 unit_size));
    which effectively requires that either low_bound is constant 0 and then
    index in ARRAY_REFs can be arbitrary type which is then sign or zero
    extended to sizetype, or low_bound is something else and then index and
    low_bound must have compatible types and it is still converted afterwards
to
    sizetype and from there then a few lines later:
    expr.c-  if (poly_int_tree_p (offset))
    expr.c-    {
    expr.c:      poly_offset_int tem = wi::sext (wi::to_poly_offset (offset),
    expr.c-                               TYPE_PRECISION (sizetype));
    The following patch makes those routines match what get_inner_reference is
    doing.

    2021-01-22  Jakub Jelinek  <jakub@redhat.com>

            PR tree-optimization/98255
            * tree-dfa.c (get_ref_base_and_extent): For ARRAY_REFs, sign
            extend index - low_bound from sizetype's precision rather than
index
            precision.
            (get_addr_base_and_unit_offset_1): Likewise.
            * tree-ssa-sccvn.c (ao_ref_init_from_vn_reference): Likewise.
            * gimple-fold.c (fold_const_aggregate_ref_1): Likewise.

            * gcc.dg/pr98255.c: New test.