[PPL-devel] FC4's GCC version 4.0.1-4.fc4 miscompiles the PPL on i386

[Roberto Bagnara]

After almost two days of struggle, it is now certain:
the version of GCC that, at the moment of writing this
message, is the standard one in Fedora Core 4/i386
miscompiles the PPL, at least at -O2 or greater
optimization level.

The problem can be seen by compiling
tests/Polyhedron/relations17.cc: at -O2 and above the
machine instruction

         movl    $2, 4

is generated, and this will of course cause a segmentation
fault.  At -O1 the right instruction, i.e.,

         movl    $2, 4(%eax)

is generated.  Many thanks to Abramo who found that
"smoking gun".

Luckily, the problem seems not to be present in the prerelease
of GCC 4.0.2 of September 13th.
Cheers,

    Roberto

-- 
Prof. Roberto Bagnara
Computer Science Group
Department of Mathematics, University of Parma, Italy
http://www.cs.unipr.it/~bagnara/
mailto:bagnara at cs.unipr.it