[Bug target/105549] aarch64: Wrong va_arg alignment handling with packed bitfields and alignment

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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105549

--- Comment #4 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Christophe Lyon <clyon@gcc.gnu.org>:

https://gcc.gnu.org/g:6610daa1cfb75b72500c22ae97988ec2a48b85c6

commit r13-5124-g6610daa1cfb75b72500c22ae97988ec2a48b85c6
Author: Christophe Lyon <christophe.lyon@arm.com>
Date:   Fri Nov 25 13:35:11 2022 +0000

    aarch64: Fix bit-field alignment in param passing [PR105549]

    While working on enabling DFP for AArch64, I noticed new failures in
    gcc.dg/compat/struct-layout-1.exp (t028) which were not actually
    caused by DFP types handling. These tests are generated during 'make
    check' and enabling DFP made generation different (not sure if new
    non-DFP tests are generated, or if existing ones are generated
    differently, the tests in question are huge and difficult to compare).

    Anyway, I reduced the problem to what I attach at the end of the new
    gcc.target/aarch64/aapcs64/va_arg-17.c test and rewrote it in the same
    scheme as other va_arg* AArch64 tests.  Richard Sandiford further
    reduced this to a non-vararg function, added as a second testcase.

    This is a tough case mixing bit-fields and alignment, where
    aarch64_function_arg_alignment did not follow what its descriptive
    comment says: we want to use the natural alignment of the bit-field
    type only if the user didn't reduce the alignment for the bit-field
    itself.

    The patch also adds a comment and assert that would help someone who
    has to look at this area again.

    The fix would be very small, except that this introduces a new ABI
    break, and we have to warn about that.  Since this actually fixes a
    problem introduced in GCC 9.1, we keep the old computation to detect
    when we now behave differently.

    This patch adds two new tests (va_arg-17.c and
    pr105549.c). va_arg-17.c contains the reduced offending testcase from
    struct-layout-1.exp for reference.  We update some tests introduced by
    the previous patch, where parameters with bit-fields and packed
    attribute now emit a different warning.

    2022-11-28  Christophe Lyon  <christophe.lyon@arm.com>
                Richard Sandiford  <richard.sandiford@arm.com>

            gcc/
            PR target/105549
            * config/aarch64/aarch64.cc (aarch64_function_arg_alignment):
            Check DECL_PACKED for bitfield.
            (aarch64_layout_arg): Warn when parameter passing ABI changes.
            (aarch64_function_arg_boundary): Do not warn here.
            (aarch64_gimplify_va_arg_expr): Warn when parameter passing ABI
            changes.

            gcc/testsuite/
            PR target/105549
            * gcc.target/aarch64/bitfield-abi-warning-align16-O2.c: Update.
            * gcc.target/aarch64/bitfield-abi-warning-align16-O2-extra.c:
Update.
            * gcc.target/aarch64/bitfield-abi-warning-align32-O2.c: Update.
            * gcc.target/aarch64/bitfield-abi-warning-align32-O2-extra.c:
Update.
            * gcc.target/aarch64/aapcs64/va_arg-17.c: New test.
            * gcc.target/aarch64/pr105549.c: New test.
            * g++.target/aarch64/bitfield-abi-warning-align16-O2.C: Update.
            * g++.target/aarch64/bitfield-abi-warning-align16-O2-extra.C:
Update.
            * g++.target/aarch64/bitfield-abi-warning-align32-O2.C: Update.
            * g++.target/aarch64/bitfield-abi-warning-align32-O2-extra.C:
Update.