http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60543
Dominique d'Humieres <dominiq at lps dot ens.fr> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |NEW
Last reconfirmed| |2014-03-16
Summary|Random number problems with |[4.8/4.9 Regression]
|REAL64 precision at |Function with side effect
|different optimization |removed by the optimizer.
|levels |
Ever confirmed|0 |1
--- Comment #1 from Dominique d'Humieres <dominiq at lps dot ens.fr> ---
Confirmed, although this has nothing to do with REAL64 precision nor with
random number. The problem comes from the fact that one call to random() is
optimized away.
On trunk (4.9) the code is optimized as with following changes:
@@ -45,7 +45,7 @@ USE globalParameters
USE generalFunctions
IMPLICIT NONE
-REAL(DP):: magnitude
+REAL(DP):: magnitude, tmp
REAL(DP):: mass
REAL(DP):: angle1, angle2
REAL(DP):: upsilon0_local, gasConstant, T
@@ -71,11 +71,12 @@ DO i=1,2000
DO
magnitude = 5e0_DP*random()
! WRITE(*,*) magnitude, EXP(-magnitude**2)
- IF ( random() <= EXP(-magnitude**2) ) EXIT
+ tmp = random()
+ IF ( tmp <= EXP(-magnitude**2) ) EXIT
END DO
! WRITE(*,*)
- angle1=random()*twopi
+ angle1=tmp*twopi
angle2=ACOS(2e0_DP*random()-1e0_DP) ; angle2=angle2-pi/2e0_DP
upsilon0_local=SQRT(2e0_DP * gasConstant * T)
For the moment I don't really understand what is happening with 4.8, i.e.,
infinite loop. AFAIU the dumps it looks optimized as
@@ -69,9 +69,10 @@ T=293.15e0_DP
DO i=1,2000
DO
- magnitude = 5e0_DP*random()
+ tmp = random()
+ magnitude = 5e0_DP*tmp
! WRITE(*,*) magnitude, EXP(-magnitude**2)
- IF ( random() <= EXP(-magnitude**2) ) EXIT
+ IF ( tmp <= EXP(-magnitude**2) ) EXIT
END DO
! WRITE(*,*)
But the executable does not hang when compiled with 4.7.4 or trunk.
