[Bug fortran/70198] simple test floating point sequence gives incorrect values-- optimizer changes them
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70198 --- Comment #7 from scott.b.dorsey at nasa dot gov --- Oh, that is lovely. Many many thanks. This code is from the "Numerical Recipes in Fortran" book and has been used around here as a standard test for the past 40 years without anyone noticing this. --scott From: dominiq at lps dot ens.fr [gcc-bugzi...@gcc.gnu.org] Sent: Saturday, March 12, 2016 4:32 AM To: s.b.dor...@larc.nasa.gov Subject: [Bug fortran/70198] simple test floating point sequence gives incorrect values-- optimizer changes them https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70198 --- Comment #6 from Dominique d'Humieres --- > If the code is compiled with the -fno-automatic option, > one generates the desired result. Note I said desired, > not correct, because the code has a significant bug. > When m=2 (see comment #4), the computed goto jumps to > label 4. The do-loop with the label 6 is executed. > The variable 'a' is undefined. It appears that this > subroutine needs a SAVE statement. Same problem with the array q. The code gives the "desired" result with the following patch --- pr70198.f 2016-03-11 22:10:39.0 +0100 +++ pr70198_db_1.f 2016-03-12 10:26:36.0 +0100 @@ -164,6 +164,7 @@ C C This routine performs Runge-Kutta calculation by Gills Method C dimension y(10),f(10),q(10) + save a, q m=m+1 go to (1,4,5,3,7), m 1 do 2 i=1,n -- You are receiving this mail because: You reported the bug.
[Bug fortran/70198] simple test floating point sequence gives incorrect values-- optimizer changes them
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70198 --- Comment #6 from Dominique d'Humieres --- > If the code is compiled with the -fno-automatic option, > one generates the desired result. Note I said desired, > not correct, because the code has a significant bug. > When m=2 (see comment #4), the computed goto jumps to > label 4. The do-loop with the label 6 is executed. > The variable 'a' is undefined. It appears that this > subroutine needs a SAVE statement. Same problem with the array q. The code gives the "desired" result with the following patch --- pr70198.f 2016-03-11 22:10:39.0 +0100 +++ pr70198_db_1.f 2016-03-12 10:26:36.0 +0100 @@ -164,6 +164,7 @@ C C This routine performs Runge-Kutta calculation by Gills Method C dimension y(10),f(10),q(10) + save a, q m=m+1 go to (1,4,5,3,7), m 1 do 2 i=1,n
[Bug fortran/70198] simple test floating point sequence gives incorrect values-- optimizer changes them
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70198 kargl at gcc dot gnu.org changed: What|Removed |Added Status|WAITING |RESOLVED Resolution|--- |INVALID --- Comment #5 from kargl at gcc dot gnu.org --- If the code is compiled with the -fno-automatic option, one generates the desired result. Note I said desired, not correct, because the code has a significant bug. When m=2 (see comment #4), the computed goto jumps to label 4. The do-loop with the label 6 is executed. The variable 'a' is undefined. It appears that this subroutine needs a SAVE statement. subroutine runge(n,y,f,x,h,m,k) C This routine performs Runge-Kutta calculation by Gills Method C dimension y(10),f(10),q(10) m=m+1 go to (1,4,5,3,7), m 1 do 2 i=1,n 2 q(i)=0 a=.5 go to 9 3 a=1.7071067811865475244 4 x=x+.5*h 5 do 6 i=1,n y(i)=y(i)+a*(f(i)*h-q(i)) 6 q(i)=2.*a*h*f(i)+(1.-3.*a)*q(i) a=.2928932188134524756 go to 9 7 do 8 i=1,n 8 y(i)=y(i)+h*f(i)/6.-q(i)/3. m=0 k=2 go to 10 9 k=1 10 return end
[Bug fortran/70198] simple test floating point sequence gives incorrect values-- optimizer changes them
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70198 kargl at gcc dot gnu.org changed: What|Removed |Added Status|UNCONFIRMED |WAITING Last reconfirmed||2016-03-11 CC||kargl at gcc dot gnu.org Ever confirmed|0 |1 --- Comment #4 from kargl at gcc dot gnu.org --- Seems that the code may be broken. % gfc6 -g -finit-real=ZERO -ffpe-trap=invalid -o z a.f % ./z Minf= 3.50 Shock angle(deg)=17.664 Cone half-angle(deg)=12.41 ***Soln only valid for ThetaC
[Bug fortran/70198] simple test floating point sequence gives incorrect values-- optimizer changes them
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70198 --- Comment #3 from Andrew Pinski --- (In reply to Andrew Pinski from comment #2) > Can you add -ffloat-store as a gcc option and try again? If that works then it is a dup of bug 323. >It's clear what is going on is not a precision problem No it is not clear yet.
[Bug fortran/70198] simple test floating point sequence gives incorrect values-- optimizer changes them
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70198 --- Comment #2 from Andrew Pinski --- Can you add -ffloat-store as a gcc option and try again?
[Bug fortran/70198] simple test floating point sequence gives incorrect values-- optimizer changes them
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70198 --- Comment #1 from Scott (Kludge) Dorsey --- Created attachment 37943 --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=37943=edit correct output sample (run on vax)
