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From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug middle-end/107208] [aarch64] _complex integer return types
 could be improved
Date: Tue, 11 Oct 2022 04:30:55 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D107208

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|[aarch64] llvm generate     |[aarch64] _complex integer
                   |better code than gcc base   |return types could be
                   |on _Complex type mul        |improved
          Component|rtl-optimization            |middle-end
   Last reconfirmed|                            |2022-10-11
             Status|UNCONFIRMED                 |NEW
     Ever confirmed|0                           |1

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Yes it is due to return value and how it is done:

(insn 32 28 33 2 (clobber (reg/i:CDI 0 x0)) "/app/example.cpp":6:1 -1
     (nil))
(insn 33 32 34 2 (set (reg:DI 0 x0)
        (reg:DI 102 [ <retval> ])) "/app/example.cpp":6:1 -1
     (nil))
(insn 34 33 35 2 (set (reg:DI 1 x1 [+8 ])
        (reg:DI 103 [ <retval>+8 ])) "/app/example.cpp":6:1 -1
     (nil))
(insn 35 34 0 2 (use (reg/i:CDI 0 x0)) "/app/example.cpp":6:1 -1
     (nil))


So this is not _Complex integer multiplies at all but rather just the return
values and the register allocator.

I wonder why Complex float is expanded slightly differently (and better her=
e):

(insn 34 33 35 2 (set (reg:SF 32 v0)
        (reg:SF 115)) "/app/example.cpp":6:1 -1
     (nil))
(insn 35 34 36 2 (set (reg:SF 33 v1)
        (reg:SF 118)) "/app/example.cpp":6:1 -1
     (nil))
(insn 36 35 37 2 (use (reg:SF 32 v0)) "/app/example.cpp":6:1 -1
     (nil))
(insn 37 36 0 2 (use (reg:SF 33 v1)) "/app/example.cpp":6:1 -1
     (nil))

Who chose CDI for the integer case but a pair of SF for the float case ...=