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From: "mjr19 at cam dot ac.uk" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/114324] [13/14/15 Regression] AVX2 vectorisation performance regression with gfortran 13/14
Date: Wed, 01 May 2024 13:21:38 +0000	[thread overview]
Message-ID: <bug-114324-4-qhmCr5FvMO@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-114324-4@http.gcc.gnu.org/bugzilla/>

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114324

--- Comment #5 from mjr19 at cam dot ac.uk ---
Note that bug 114767 also turns out to be a case in which the inability to
alternate neg and nop along a vector leads to poor performance with some
operations on the complex type. That optimisation improvement request also
discusses that the ability to alternate add and nop could be beneficial.

Ifort can alternate neg and nop, at least in the simple case of

  complex(kind(1d0)) :: c(*)
  do i=1,n
     c(i)=conjg(c(i))
  enddo

Helped by aggressive default unrolling, it ends up being almost four times
faster than gfortran-14 on the machine I tested it on. On asking gfortran-14 to
unroll, the difference is reduced to about a factor of two.

  parent reply	other threads:[~2024-05-01 13:21 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2024-03-13 12:52 [Bug fortran/114324] New: " mjr19 at cam dot ac.uk
2024-03-13 19:45 ` [Bug tree-optimization/114324] [13/14 Regression] " pinskia at gcc dot gnu.org
2024-03-14  8:32 ` rguenth at gcc dot gnu.org
2024-03-14  8:32 ` rguenth at gcc dot gnu.org
2024-03-14 10:37 ` rguenth at gcc dot gnu.org
2024-03-15 20:06 ` mjr19 at cam dot ac.uk
2024-05-01 13:21 ` mjr19 at cam dot ac.uk [this message]
2024-05-21  9:19 ` [Bug tree-optimization/114324] [13/14/15 " jakub at gcc dot gnu.org

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