https://gcc.gnu.org/bugzilla/show_bug.cgi?id=121570
Thomas Koenig <tkoenig at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |tkoenig at gcc dot gnu.org
Status|UNCONFIRMED |NEW
Keywords| |missed-optimization
Severity|normal |enhancement
Last reconfirmed| |2025-08-17
Ever confirmed|0 |1
--- Comment #3 from Thomas Koenig <tkoenig at gcc dot gnu.org> ---
Looking at https://godbolt.org/z/x3d8q4Krd , ifx is translating
the loop in the shortened code
program main
!..use and access
use iso_fortran_env, only : int32, real32, real64
use ieee_arithmetic
implicit none
!..data
integer (kind=int32) :: i32, j32
real (kind=real32) :: t32, r32
real (kind=real64) :: tim0, tim1
!..executable part
j32 = huge(0_int32)
i32 = -j32-1
r32 = 0
call cpu_time(tim0)
do while (r32.ne.t32)
r32 = ieee_next_after(r32,t32)
end do
call cpu_time (tim1)
write (*,'(a25,1pg9.2,1pg16.9)') &
'2^32 ieee_next_after:', tim1-tim0, r32
stop
end program main
into
movq %rbx, %rdi
movq %r14, %rsi
callq __for_ieee_next_after_k4_@PLT
movss %xmm0, 12(%rsp)
ucomiss 16(%rsp), %xmm0
jne .LBB0_1
jp .LBB0_1
whereas gfortran does
movq %rbx, %rdi
movss %xmm0, 8(%rsp)
call _gfortran_ieee_procedure_entry
movss 8(%rsp), %xmm0
pxor %xmm1, %xmm1
movss %xmm1, 12(%rsp)
call nextafterf
movq %rbx, %rdi
movss %xmm0, 20(%rsp)
movss %xmm0, 8(%rsp)
call _gfortran_ieee_procedure_exit
movss 8(%rsp), %xmm0
ucomiss 12(%rsp), %xmm0
I cannot look at what ifx's __for_ieee_next_after_k4_ does, but
a separate, more optimized implementation for ieee_next_after might
be faster also for gfortran. For example, it could check its argument
if the operation will raise an exception, and branch in that event
(which could be marked as unlikely, and after a few iterations, would
be marked as unlikely to be taken by the CPU).
Confirmed as an enhancement request.
