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
c(i)=a(i)*(0d0,1d0
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 gfortran
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
Priority: P3
Component: fortran
Assignee: unassigned at gcc dot gnu.org
Reporter: mjr19 at cam dot ac.uk
Target Milestone: ---
Gfortran 14 shows considerable improvement over 13.1 on x86_64 AVX2 on the test
case
subroutine scale_i(c,n)
integer :: i,n
complex
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 m
Priority: P3
Component: fortran
Assignee: unassigned at gcc dot gnu.org
Reporter: mjr19 at cam dot ac.uk
Target Milestone: ---
Created attachment 57685
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=57685=edit
Test case of loop showing performance regress
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92698
--- Comment #2 from mjr19 at cam dot ac.uk ---
Thomas is quite correct that I had failed to mark the array as contiguous, at
which point the double copy is more reasonable (although memcpy will also
expect its arguments to be contiguous).
He
: fortran
Assignee: unassigned at gcc dot gnu.org
Reporter: mjr19 at cam dot ac.uk
Target Milestone: ---
subroutine cpy(a,src,dest,len)
integer, intent(in) :: src,dest,len
real(kind(1d0)), intent(inout) :: a(:)
a(dest:dest+len-1)=a(src:src+len-1)
end subroutine cpy
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