[BuildTools-tickets] [BuildTools] #66: Lapack hangs in dlamc1 if in optimized build

[BuildTools]

#66: Lapack hangs in dlamc1 if in optimized build
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Reporter:  stefan  |       Owner:  andreasw           
    Type:  defect  |      Status:  new                
Priority:  major   |   Component:  configuration tests
 Version:  0.5     |    Keywords:                     
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 Hi,

 in some cases, CBC (2.1 stable) and SCIP (1.0; using Clp as LP solver)
 hang in the Lapack routine {{{dlamc1}}} if I have compiled in optimized
 mode (i.e., default).

 The compiler is a GCC 4.2.1, the machine a Intel Core2 Duo.

 John pointed me to
 [http://osdir.com/ml/gnu.octave.bugs/2005-10/msg00042.html this ticket] in
 the Octave mailing list. I followed the suggestions there and the problem
 went away when I added {{{-ffloat-store}}} to the FFLAGS.

 Should this flag be added per default (when gcc is used), at least for
 {{{dlamch.f}}} ?

 Best,
 Stefan

 PS: This is from the gcc manual on what {{{-ffloat-store}}} is doing:

 Do not store floating point variables in registers, and inhibit other
 options that might change whether a floating point value is taken from a
 register or memory.

 This option prevents undesirable excess precision on machines such as the
 68000 where the floating registers (of the 68881) keep more precision than
 a "double" is supposed to have.  Similarly for the x86 architecture.  For
 most programs, the excess precision does only good, but a few programs
 rely on the precise definition of IEEE floating point.  Use -ffloat-store
 for such programs, after modifying them to store all pertinent
 intermediate computations into variables.

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Ticket URL: <https://projects.coin-or.org/BuildTools/ticket/66>
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