------- Comment #1 from pinskia at gmail dot com 2010-04-04 06:28 -------
Subject: Re: New: Missed optimization with complex long double
Sent from my iPhone
On Apr 3, 2010, at 11:21 PM, "svfuerst at gmail dot com"
<gcc-bugzi...@gcc.gnu.org
> wrote:
> gcc 4.4 compiles the following:
>
> _Complex long double foo(long double p1, long double p2)
> {
> return p1 + (__extension__ 1.0iF) * p2;
> }
>
> gcc-4.4 -O3 tgcc.c -c -o tgcc.o
>
> into
>
> 0x0000000000000000 <+0>: fldt 0x8(%rsp)
> 0x0000000000000004 <+4>: fldt 0x18(%rsp)
> 0x0000000000000008 <+8>: fxch %st(1)
> 0x000000000000000a <+10>: retq
>
> This is ok, except for the useless fxch instruction. However, gcc
> 4.5 compiles
> the same code into:
> gcc-4.5 -O3 tgcc.c -c -o tgcc.o
>
> 0x0000000000000000 <+0>: fldt 0x18(%rsp)
> 0x0000000000000004 <+4>: fld %st(0)
> 0x0000000000000006 <+6>: fmuls 0x0(%rip) # 0xc <foo+12>
> 0x000000000000000c <+12>: fldt 0x8(%rsp)
> 0x0000000000000010 <+16>: faddp %st,%st(1)
> 0x0000000000000012 <+18>: retq
>
> which is quite a bit worse.
Except it is needed for handling -0.0 correctly.
>
>
> --
> Summary: Missed optimization with complex long double
> Product: gcc
> Version: unknown
> Status: UNCONFIRMED
> Severity: normal
> Priority: P3
> Component: c
> AssignedTo: unassigned at gcc dot gnu dot org
> ReportedBy: svfuerst at gmail dot com
> GCC build triplet: x86_64-linux
> GCC host triplet: x86_64-linux
> GCC target triplet: x86_64-linux
>
>
> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43639
>
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43639
