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).