[Bug rtl-optimization/7061] Access of bytes in struct parameters

[Bug rtl-optimization/7061] Access of bytes in struct parameters

[gabravier at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=7061

Gabriel Ravier <gabravier at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |gabravier at gmail dot com

--- Comment #7 from Gabriel Ravier <gabravier at gmail dot com> ---
Compiling this under ia64 seems to now be optimized perfectly as of at least
GCC 10, though the other ones look like they're still badly handled.

[Bug rtl-optimization/7061] Access of bytes in struct parameters

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=7061

--- 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:1ad584d538d349db13cfa8440222d91d5e9aff3f

commit r13-859-g1ad584d538d349db13cfa8440222d91d5e9aff3f
Author: Roger Sayle <roger@nextmovesoftware.com>
Date:   Mon May 30 21:32:58 2022 +0100

    Allow SCmode and DImode to be tieable with TARGET_64BIT on x86_64.

    This patch is a form of insurance policy in case my patch for PR 7061 runs
    into problems on non-x86 targets; the middle-end can add an extra check
    that the backend is happy placing SCmode and DImode values in the same
    register, before creating a SUBREG.  Unfortunately, ix86_modes_tieable_p
    currently claims this is not allowed(?), even though the default target
    hook for modes_tieable_p is to always return true [i.e. false can be
    used to specifically prohibit bad combinations], and the x86_64 ABI
    passes SCmode values in DImode registers!.  This makes the backend's
    modes_tiable_p hook a little more forgiving, and additionally enables
    interconversion between SCmode and V2SFmode, and between DCmode and
    VD2Fmode, which opens interesting opporutunities in the future.

    2022-05-30  Roger Sayle  <roger@nextmovesoftware.com>

    gcc/ChangeLog
            * config/i386/i386.cc (ix86_modes_tieable_p): Allow SCmode to be
            tieable with DImode on TARGET_64BIT, and SCmode tieable with
            V2SFmode, and DCmode with V2DFmode.

[Bug rtl-optimization/7061] Access of bytes in struct parameters

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=7061

--- Comment #9 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:1753a7120109c1d3b682f9487d6cca64fb2f0929

commit r13-1038-g1753a7120109c1d3b682f9487d6cca64fb2f0929
Author: Roger Sayle <roger@nextmovesoftware.com>
Date:   Fri Jun 10 15:14:23 2022 +0100

    PR rtl-optimization/7061: Complex number arguments on x86_64-like ABIs.

    This patch addresses the issue in comment #6 of PR rtl-optimization/7061
    (a four digit PR number) from 2006 where on x86_64 complex number arguments
    are unconditionally spilled to the stack.

    For the test cases below:
    float re(float _Complex a) { return __real__ a; }
    float im(float _Complex a) { return __imag__ a; }

    GCC with -O2 currently generates:

    re:     movq    %xmm0, -8(%rsp)
            movss   -8(%rsp), %xmm0
            ret
    im:     movq    %xmm0, -8(%rsp)
            movss   -4(%rsp), %xmm0
            ret

    with this patch we now generate:

    re:     ret
    im:     movq    %xmm0, %rax
            shrq    $32, %rax
            movd    %eax, %xmm0
            ret

    [Technically, this shift can be performed on %xmm0 in a single
    instruction, but the backend needs to be taught to do that, the
    important bit is that the SCmode argument isn't written to the
    stack].

    The patch itself is to emit_group_store where just before RTL
    expansion commits to writing to the stack, we check if the store
    group consists of a single scalar integer register that holds
    a complex mode value; on x86_64 SCmode arguments are passed in
    DImode registers.  If this is the case, we can use a SUBREG to
    "view_convert" the integer to the equivalent complex mode.

    An interesting corner case that showed up during testing is that
    x86_64 also passes HCmode arguments in DImode registers(!), i.e.
    using modes of different sizes.  This is easily handled/supported
    by first converting to an integer mode of the correct size, and
    then generating a complex mode SUBREG of this.  This is similar
    in concept to the patch I proposed here:
    https://gcc.gnu.org/pipermail/gcc-patches/2022-February/590139.html

    2020-06-10  Roger Sayle  <roger@nextmovesoftware.com>

    gcc/ChangeLog
            PR rtl-optimization/7061
            * expr.cc (emit_group_store): For groups that consist of a single
            scalar integer register that hold a complex mode value, use
            gen_lowpart to generate a SUBREG to "view_convert" to the complex
            mode.  For modes of different sizes, first convert to an integer
            mode of the appropriate size.

    gcc/testsuite/ChangeLog
            PR rtl-optimization/7061
            * gcc.target/i386/pr7061-1.c: New test case.
            * gcc.target/i386/pr7061-2.c: New test case.

[Bug rtl-optimization/7061] Access of bytes in struct parameters

[david.bolvansky at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=7061

Dávid Bolvanský <david.bolvansky at gmail dot com> changed:

           What    |Removed                     |Added
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                 CC|                            |david.bolvansky at gmail dot com

--- Comment #10 from Dávid Bolvanský <david.bolvansky at gmail dot com> ---
llvm emits just:
im:                                     # @im
        shufps  xmm0, xmm0, 85                  # xmm0 = xmm0[1,1,1,1]
        ret

[Bug rtl-optimization/7061] Access of bytes in struct parameters

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=7061

--- Comment #11 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:64d4f27a0ce47e97867512bda7fa5683acf8a134

commit r13-1282-g64d4f27a0ce47e97867512bda7fa5683acf8a134
Author: Roger Sayle <roger@nextmovesoftware.com>
Date:   Mon Jun 27 07:47:40 2022 +0100

    Implement __imag__ of float _Complex using shufps on x86_64.

    This patch is a follow-up improvement to my recent patch for
    PR rtl-optimization/7061.  That patch added the test case
    gcc.target/i386/pr7061-2.c:

    float im(float _Complex a) { return __imag__ a; }

    For which GCC on x86_64 currently generates:

            movq    %xmm0, %rax
            shrq    $32, %rax
            movd    %eax, %xmm0
            ret

    but with this patch we now generate (the same as LLVM):

            shufps  $85, %xmm0, %xmm0
            ret

    This is achieved by providing a define_insn_and_split that allows
    truncated lshiftrt:DI by 32 to be performed on either SSE or general
    regs, where if the register allocator prefers to use SSE, we split
    to a shufps_v4si, or if not, we use a regular shrq.

    2022-06-27  Roger Sayle  <roger@nextmovesoftware.com>

    gcc/ChangeLog
            PR rtl-optimization/7061
            * config/i386/i386.md (*highpartdisi2): New define_insn_and_split.

    gcc/testsuite/ChangeLog
            PR rtl-optimization/7061
            * gcc.target/i386/pr7061-2.c: Update to look for shufps.

[Bug rtl-optimization/7061] Access of bytes in struct parameters

[rth at gcc dot gnu dot org]

------- Comment #5 from rth at gcc dot gnu dot org  2005-11-02 08:09 -------
And there is nothing Alpha specific about this.  Any target which passes
structures in registers can show it.  For instance, ia64:

f1:
        .prologue
        .body
        .mmi
        st2 [r12] = r32
        nop 0
        mov r14 = r12
        ;;
        .mmi
        ld1 r15 = [r14], 1
        ;;
        ld1 r8 = [r14]
        nop 0
        ;;
        .mib
        nop 0
        add r8 = r8, r15
        br.ret.sptk.many b0
        .endp f1#
        .align 16
        .global f2#
        .proc f2#
f2:
        .prologue
        .body
        .mii
        nop 0
        extr.u r8 = r32, 8, 8
        zxt1 r32 = r32
        ;;
        .mib
        nop 0
        add r8 = r8, r32
        br.ret.sptk.many b0


-- 

rth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   GCC host triplet|alphapca56-*-linux-gnu      |
 GCC target triplet|alphapca56-*-linux-gnu      |
            Summary|Alpha: Access of bytes in   |Access of bytes in struct
                   |struct parameters           |parameters


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=7061

[Bug rtl-optimization/7061] Access of bytes in struct parameters

[pluto at agmk dot net]

------- Comment #6 from pluto at agmk dot net  2006-02-08 21:10 -------
one more testcase from x86-64 / gcc-4.1:

float re(float _Complex a) { return __real__ a; }

is compiled to:

re: movq    %xmm0, -8(%rsp)
    movss   -8(%rsp), %xmm0
    ret

but can be optimized to `movss %xmm0, %xmm0`.


-- 

pluto at agmk dot net changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |pluto at agmk dot net


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=7061