https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114767
--- Comment #7 from mjr19 at cam dot ac.uk ---
Another manifestation of this issue in GCC 13.1 and 14.1 is that the loop
do i=1,n
c(i)=a(i)*c(i)*(0d0,1d0)
enddo
takes about twice as long to run as
do i=1,n
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
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114767
--- Comment #6 from mjr19 at cam dot ac.uk ---
I was starting to wonder whether this issue might be related to that in bug
114324, which is a slightly more complicated example in which multiplication by
a purely imaginary number destroys
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114767
--- Comment #4 from mjr19 at cam dot ac.uk ---
An issue which I suspect is related is shown by
subroutine zradd(c,n)
integer :: i,n
complex(kind(1d0)) :: c(*)
do i=1,n
c(i)=c(i)+1d0
enddo
end subroutine
If compiled with
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114767
--- Comment #2 from mjr19 at cam dot ac.uk ---
Ah, I see. An inability to alternate negation with noop also means that
conjugation is treated suboptimally.
do i=1,n
c(i)=conjg(c(i))
enddo
Here gfortran-13 and -14 are differently
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114767
Bug ID: 114767
Summary: gfortran AVX2 complex multiplication by (0d0,1d0)
suboptimal
Product: gcc
Version: 14.0
Status: UNCONFIRMED
Severity: normal
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114324
--- Comment #4 from mjr19 at cam dot ac.uk ---
Created attachment 57713
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=57713=edit
Second testcase, very similar to first
Thank you for looking into this. The real code in question has more
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114324
Bug ID: 114324
Summary: AVX2 vectorisation performance regression with
gfortran 13/14
Product: gcc
Version: 13.1.0
Status: UNCONFIRMED
Severity: normal
