[Bug target/83920] [nvptx] bad predicate reset

["vries at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83920

--- Comment #6 from Tom de Vries <vries at gcc dot gnu.org> ---
(In reply to Tom de Vries from comment #3)
> Likewise, reversing the if-then-else order in gemm.f90 makes the testcase
> fail on trunk without this patch.

Minimal version:
...
! { dg-do run }                                                                 

subroutine gemm (BETA, C)
  real ::  C(100,100)
  integer :: i, j, l
  real, parameter :: one = 1.0
  real :: beta

  !$acc parallel copy(c(1:100,1:100)) num_gangs(2)                              
  !$acc loop gang                                                               
  do j = 1, 100
     if (beta /= one) then
        !$acc loop vector                                                       
        do i = 1, 100
           C(i,j) = 0.0
        end do
     end if
  end do
  !$acc end parallel                                                            
end subroutine gemm

program test_gemm
  real :: c(100,100), beta
  beta = 0.0
  c(:,:) = 1.0
  call gemm (beta, c)
  if (c(1,1) /= 0.0) call abort ()
end program test_gemm
...

Passes at O0, fails at O1 and higher.