https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99355
Bug ID: 99355
Summary: -freal-X-real-Y -freal-Z-real-X promotes Z to Y
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: fortran
Assignee: unassigned at gcc dot gnu.org
Reporter: nickpapior at gmail dot com
Target Milestone: ---
Created attachment 50291
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=50291&action=edit
Same as code snippet
I came about this in LAPACK which allows compiling in quad precision.
However, mixed precision algorithms will no longer be mixed precision since
*everything* gets promoted.
See this code snippet (and attached as well):
program test
real :: r1
real*4:: r2
real(4) :: r3
real(selected_real_kind(p=6)) :: r4
double precision :: d1
real*8 :: d2
real(8) :: d3
real(kind(1.d0)) :: d4
real(selected_real_kind(p=15)) :: d5
print '(tr3,a10,10(tr1,i2))', 'single', kind(r1), kind(r2), kind(r3),
kind(r4)
print '(tr3,a10,10(tr1,i2))', 'double', kind(d1), kind(d2), kind(d3),
kind(d4), kind(d5)
end program test
Here listed with 4 different flag combinations:
#FLAGS =
single 4 4 4 4
double 8 8 8 8 8
#FLAGS = -freal-4-real-8
single 8 8 8 8
double 8 8 8 8 8
#FLAGS = -freal-8-real-16
single 4 4 4 4
double 16 16 16 16 16
#FLAGS = -freal-8-real-16 -freal-4-real-8 (order doesn't matter)
single 8 16 16 16
double 16 16 16 16 16
The first 3 flag combinations works as intended.
The last one behaves bad.
I would have expected 8->16 and 4->8 (without double promotion).
