AMD Backend Failure

We have see in the past some examples of source code given which FTN95 /64 runs into an 'AMD backend failure'. Here is another example, which is fairly short and contains only one line with a matrix expression using user defined matrix multiply and matrix-transpose multiply operators.

The code compiles fine with FTN95 8.51, 32-bit, and other compilers such as Gfortran. FTN95 8.51 fails with /64.

*** AMD backend failure:Failed to do memory-register emit for MOVSS at 754

The source code:

   module linear_oper
   implicit none

   interface operator(.x.)
      module procedure MultAB, MultAv
   end interface

   interface operator(.tx.)
      module procedure MultATB, MultATv
   end interface

   interface
      subroutine gemv(A,b,v,trans)
         real :: A(:,:), b(:), v(:)
         character(1), optional :: trans
      end subroutine

      subroutine gemm(A,B,C,transa)
         real :: A(:,:), B(:,:), C(:,:)
         character(1), optional :: transa
      end subroutine
   end interface

   contains
      function MultAB(a, b)
         real, dimension(:,:), intent(in) :: a,b
         real, dimension(size(a,1),size(b,2)) :: MultAB
         call gemm(a,b, MultAB)
      end function MultAB

      function MultAv(a, b)
         real, dimension(:,:), intent(in) :: a
         real, dimension(:),   intent(in) :: b
         real, dimension(size(a,1)) :: MultAv
         call gemv(a,b, MultAv)
      end function MultAv

      function MultATB(a, b)
         real, dimension(:,:), intent(in) :: a,b
         real, dimension(size(a,2),size(b,2)) :: MultATB
         call gemm(a,b, MultATB, transa='T')
      end function MultATB

      function MultATv(a, b)
         real, dimension(:,:), intent(in) :: a
         real, dimension(:),   intent(in) :: b
         real, dimension(size(a,2)) :: MultATv
         call gemv(a,b, MultATv,trans='T')
      end function MultATv

   end module linear_oper

subroutine tor_modal_dec(eigvec,mtt,mmt,n)

   use linear_oper
   implicit none
   integer :: n
   real :: mtt(n,n), mmt(n,n), eigvec(n,n)

   mmt(:,:) = eigvec(:,1:n) .tx. mtt .x. eigvec(:,1:n)

end subroutine tor_modal_dec

mecej4

Thank you for the bug report which I have logged for investigation.

mecej4

This bug has now been fixed. Do you have some code for GEMV and GEMM so that I can test to see if the results are compatible with 32 bits etc.?

Paul,

Here is some fake GEMV and GEMM code (the fake subroutines do not have the standard BLAS or BLAS95 interfaces), and a driver, just to enable you to build and run.

BLAS.f90:

      subroutine gemv(A,b,v,trans)
         real :: A(:,:), b(:), v(:)
         character(1), optional :: trans
         integer m, n, i
         m = size(A,1); n = size(A,2)
         if (.not. present(trans)) then
            do i=1,m
               v(i) = dot_product(A(i,:),b)
            end do
            return
         end if
         if (trans.ne.'T' .and. trans.ne.'t') then
            do i=1,m
               v(i) = dot_product(A(i,:),b)
            end do
            return
         else
            do i = 1, n
               v(i) = dot_product(A(:,i),b)
            end do
         endif
         return
       end subroutine gemv

       subroutine gemm(A,B,C,transa)
          real :: A(:,:), B(:,:), C(:,:)
          character(1), optional :: transa
          integer m, n, k, i, j
          if(present(transa)) then
             if(transa.eq.'t'.or.transa.eq.'T')goto 100
          endif
          m = size(A,1); n = size(A,2); k= size(B,2)
          do i=1,m
             do j=1,k
                C(i,j) = dot_product(A(i,:),B(:,j))
             end do
          end do
          return
   100 continue
          m = size(A,2); n = size(A,1); k = size(B,2)
          do i=1,m
             do j=1,k
                C(i,j) = dot_product(A(:,i),B(:,j))
             end do
          end do
          return

       end subroutine

DRIVER.f90:

program testxtAx

implicit none
integer i
real :: A(3,3),X(3,3),M(3,3)

A = reshape((/ 2.,-1.,1.5,-1.,2.,-1.,1.5,-1.,2. /), (/3,3/))
X = reshape((/2.,-1.,3.,-1.,2.,-1.,3.,-1.,2./),(/3,3/))

call tor_modal_dec(X,A,M,3)

print 10,(M(i,:),i=1,3)

10 format(1x,3ES15.5)
end program

The expected output:

     5.60000E+01   -3.35000E+01    5.55000E+01
    -3.35000E+01    2.30000E+01   -3.35000E+01
     5.55000E+01   -3.35000E+01    5.60000E+01

For this example, FTN95 V8.51 and 7.20 give 32-bit EXEs that produce an X87 stack fault. The fault occurs after the r.h.s. of the only executable statement in TOR_MODEL_DEC() has been evaluated and when the result is being copied to the l.h.s.

This failure has now been fixed for the next release of FTN95.

The failure can be avoided by removing the redundant sections in

mmt(:,:) = eigvec(:,1:n) .tx. mtt .x. eigvec(:,1:n)