https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108329
Bug ID: 108329
Summary: IEEE_SET_ROUNDING_MODE ineffective with common
subexpression elimination
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: fortran
Assignee: unassigned at gcc dot gnu.org
Reporter: tkoenig at gcc dot gnu.org
Target Milestone: ---
Split from https://gcc.gnu.org/bugzilla/show_bug.cgi?id=34678#c47 .
The test case
$ cat y.f90
module y
implicit none
integer, parameter :: wp = selected_real_kind(15)
contains
subroutine foo(a,b,c)
use ieee_arithmetic
real(kind=wp), dimension(4), intent(out) :: a
real(kind=wp), intent(in) :: b, c
type (ieee_round_type), dimension(4), parameter :: mode = &
[ieee_nearest, ieee_to_zero, ieee_up, ieee_down]
call ieee_set_rounding_mode (mode(1))
a(1) = b + c
call ieee_set_rounding_mode (mode(2))
a(2) = b + c
call ieee_set_rounding_mode (mode(3))
a(3) = b + c
call ieee_set_rounding_mode (mode(4))
a(4) = b + c
end subroutine foo
end module y
program main
use y
real(kind=wp), dimension(4) :: a
call foo(a, 0.1_wp, 0.2_wp)
print *,a
end program main
$ gfortran -O y.f90 && ./a.out
0.30000000000000004 0.30000000000000004 0.30000000000000004
0.30000000000000004
$ gfortran y.f90 && ./a.out
0.30000000000000004 0.29999999999999999 0.30000000000000004
0.29999999999999999
shows that common subexpression removal causes the addition to be performed
only once.
