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)*c(i)
enddo
when compiled -Ofast -mavx2. In the second case the compiler manages to merge
its unnecessary desire to form separate vectors of real and imaginary
components to perform the sign flips on multiplying by i, with its much more
reasonable desire to form such vectors for the general complex-complex
multiplication.
One might also argue that, as the above expressions are mathematically
identical, at -Ofast the compiler ought to chose the faster anyway.
