[Bug middle-end/95126] [10/11/12/13 Regression] Missed opportunity to turn static variables into immediates

["cvs-commit at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95126

--- Comment #8 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Roger Sayle <sayle@gcc.gnu.org>:

https://gcc.gnu.org/g:ed6fd2aed58f2cca99f15331bf68999c0e6df370

commit r13-990-ged6fd2aed58f2cca99f15331bf68999c0e6df370
Author: Roger Sayle <roger@nextmovesoftware.com>
Date:   Sat Jun 4 12:21:51 2022 +0100

    PR middle-end/95126: Expand small const structs as immediate constants.

    This patch resolves PR middle-end/95126 which is a code quality regression,
    by teaching the RTL expander to emit small const structs/unions as integer
    immediate constants.

    The motivating example from the bugzilla PR is:

    struct small{ short a,b; signed char c; };
    extern int func(struct small X);
    void call_func(void)
    {
        static struct small const s = { 1, 2, 0 };
        func(s);
    }

    which on x86_64 is currently compiled to:

    call_func:
            movzwl  s.0+2(%rip), %eax
            movzwl  s.0(%rip), %edx
            movzwl  s.0+4(%rip), %edi
            salq    $16, %rax
            orq     %rdx, %rax
            salq    $32, %rdi
            orq     %rax, %rdi
            jmp     func

    but with this patch is now optimized to:

    call_func:
            movl    $131073, %edi
            jmp     func

    2022-06-04  Roger Sayle  <roger@nextmovesoftware.com>

    gcc/ChangeLog
            PR middle-end/95126
            * calls.cc (load_register_parameters): When loading a suitable
            immediate_const_ctor_p VAR_DECL into a single word_mode register,
            construct it directly in a pseudo rather than read it (by parts)
            from memory.
            * expr.cc (int_expr_size): Make tree argument a const_tree.
            (immediate_const_ctor_p): Helper predicate.  Return true for
            simple constructors that may be materialized in a register.
            (expand_expr_real_1) [VAR_DECL]: When expanding a constant
            VAR_DECL with a suitable immediate_const_ctor_p constructor
            use store_constructor to materialize it directly in a pseudo.
            * expr.h (immediate_const_ctor_p): Prototype here.
            * varasm.cc (initializer_constant_valid_for_bitfield_p): Change
            VALUE argument from tree to const_tree.
            * varasm.h (initializer_constant_valid_for_bitfield_p): Update
            prototype.

    gcc/testsuite/ChangeLog
            PR middle-end/95126
            * gcc.target/i386/pr95126-m32-1.c: New test case.
            * gcc.target/i386/pr95126-m32-2.c: New test case.
            * gcc.target/i386/pr95126-m32-3.c: New test case.
            * gcc.target/i386/pr95126-m32-4.c: New test case.
            * gcc.target/i386/pr95126-m64-1.c: New test case.
            * gcc.target/i386/pr95126-m64-2.c: New test case.
            * gcc.target/i386/pr95126-m64-3.c: New test case.
            * gcc.target/i386/pr95126-m64-4.c: New test case.