https://gcc.gnu.org/bugzilla/show_bug.cgi?id=62283
--- Comment #7 from Richard Biener <rguenth at gcc dot gnu.org> --- (In reply to Richard Biener from comment #6) > (In reply to Henrik Holst from comment #4) > > Thank you Richard for looking into this issue. > > > > You probably know already exactly why this bug appeared. I just wanted to > > stress the severity of this issue, and especially for Fortran which is often > > used in "number crunching" applications AND subroutine arguments are passed > > by reference by default. > > > > The following F2008 code works as expected: > > > > subroutine test1(x,y) > > real x(4),y(4) > > gamma=3.141593 > > block > > beta=gamma > > y(1)=y(1)+beta*x(1) > > y(2)=y(2)+beta*x(2) > > y(3)=y(3)+beta*x(3) > > y(4)=y(4)+beta*x(4) > > end block > > end > > > > but when `beta=gamma` is replaced with `beta=alpha` it again fails and > > generates scalar code. So I ask: Does this bug force *ALL* computations > > which involves directly or indirectly parameter values to subroutines and > > functions, to be done in scalar? If so, its pretty bad. > > For basic-block vectorization? It depends whether the first use of > the indirect parameter is in the same basic-block that is supposed > to be vectorized or not ... > > > Related or not, the following codes also generates scalar code: > > > > subroutine test2(x,y) > > real x(4),y(4) > > beta=3.141593 > > do i=1,4 > > y(i)=y(i)+beta*x(i) > > end do > > end > > That's because we decide to peel for alignment and then decide the > result is not profitable to vectorize. With -fno-vect-cost-model > the loop is vectorized (but in an awkward way). You may want to > file a separate bug about this. > > > and > > > > subroutine test3(x,y) > > real x(4),y(4) > > beta=3.141593 > > y=y+beta*x > > end > > Same issue (add it as another testcase to the new bug). > > It is of course pointless to peel for alignment if the remaining loop > will always run less than the vectorization factor. Versioning for > alignment may still be applied here. I have a simple patch for this. > > as well. I can create another bug for this if you think they are unrelated.
