[Bug fortran/70198] simple test floating point sequence gives incorrect values-- optimizer changes them

[kargl at gcc dot gnu.org]

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
<a lot of output removed>
Minf=   3.50  Shock angle(deg)=17.664  Cone half-angle(deg)=12.41

  ***Soln only valid for ThetaC<ThetaCmax***
  ***(i.e., no detached shock cases)***

          Log written to file "cone.dat"

% gfc6 -g -finit-real=SNAN -ffpe-trap=invalid -o z a.f
% ./z

 Input free-stream Mach and shock angle(deg)[<70 deg]
 -----------------------------------------------------------

 Solution to Taylor-Maccoll equation for conical flow follows:

  theta=  17.66  M= 3.40246  P/P0= 0.01507  T/T0= 0.30163  Rho/Rho0= 0.04997
Floating exception (core dumped)

% gdb710 z
Program received signal SIGFPE, Arithmetic exception.
0x0000000000400f4a in runge (n=2, y=..., f=..., x=0.308207691, 
    h=-0.000174532921, m=2, k=1) at a.f:178
178           y(i)=y(i)+a*(f(i)*h-q(i))

a appears to be uninitialized.