[Bug middle-end/105853] [13 regression] ice in pieces_addr constructor

cvs-commit at gcc dot gnu.org gcc-bugzilla@gcc.gnu.org
Tue Jun 7 09:13:27 GMT 2022


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


commit r13-1004-gc00e1e3aa5ae62a991d105d309061d12f6a8764f
Author: Roger Sayle <roger@nextmovesoftware.com>
Date:   Tue Jun 7 10:09:49 2022 +0100

    PR middle-end/105853: Call store_constructor directly from calls.cc.

    This patch fixes both ICE regressions PR middle-end/105853 and
    PR target/105856 caused by my recent patch to expand small const structs
    as immediate constants.  That patch updated code generation in three
    places: two in expr.cc that call store_constructor directly, and the
    third in calls.cc's load_register_parameters that expands its CONSTRUCTOR
    via expand_expr, as store_constructor is local/static to expr.cc, and
    the "public" API, should usually simply forward the constructor to the
    appropriate store_constructor function.

    Alas, despite the clean regression testing on multiple targets, the above
    ICEs show that expand_expr isn't a suitable proxy for store_constructor,
    and things that (I'd assumed) shouldn't affect how/whether a struct is
    placed in a register [such as whether the struct is considered packed/
    aligned or not] actually interfere with the optimization that is being

    The (proposed) solution is to export store_constructor (and it's helper
    function int_expr_size) from expr.cc, by removing their static qualifier
    and prototyping both functions in expr.h, so they can be called directly
    from load_register_parameters in calls.cc.  This cures both ICEs, but
    almost as importantly improves code generation over GCC 12.

    For PR 105853, GCC 12 generates:

            movzx eax, WORD PTR eth_addr_zero[rip+2]
            movzx edx, WORD PTR eth_addr_zero[rip]
            movzx edi, WORD PTR eth_addr_zero[rip+4]
            sal rax, 16
            or rax, rdx
            sal rdi, 32
            or rdi, rax
            xor eax, eax
            jmp packet_set_nd
    eth_addr_zero:  .zero 6

    where now (with this fix) GCC 13 generates:
            xorl    %edi, %edi
            xorl    %eax, %eax
            jmp     packet_set_nd

    Likewise, for PR 105856 on ARM, we'd previously generate:
            movw r3, #:lower16:.LANCHOR0
            movt r3, #:upper16:.LANCHOR0
            ldr r0, [r3]
            b func_19

    but with this optimization we now generate:
            mov     r0, #6
            b       func_19

    2022-06-07  Roger Sayle  <roger@nextmovesoftware.com>

            PR middle-end/105853
            PR target/105856
            * calls.cc (load_register_parameters): Call store_constructor
            and int_expr_size directly instead of expanding via expand_expr.
            * expr.cc (static void store_constructor): Don't prototype here.
            (static HOST_WIDE_INT int_expr_size): Likewise.
            (store_constructor): No longer static.
            (int_expr_size): Likewise, no longer static.
            * expr.h (store_constructor): Prototype here.
            (int_expr_size): Prototype here.

            PR middle-end/105853
            PR target/105856
            * gcc.dg/pr105853.c: New test case.
            * gcc.dg/pr105856.c: New test case.

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