[Vm-dev] failing/errors Pharo Tests with CogVM
andreas.raab at gmx.de
Thu Sep 16 20:25:30 UTC 2010
On 9/16/2010 12:32 PM, Eliot Miranda wrote:
> I need to check these carefully. One thing that does differ in
> current Cog is that the machine-code arithmetic float primitives don't
> fail if they produce a NaN result; they simply answer a NaN result. IMo
> what needs to be done is two-fold.
> a) we need a NaN mode flag in the VM, that persists across snapshots and
> e.g. is queryable/settable via vmParameterAt:put:, that puts the
> floating-pont primitive into a state where NaNs are answered instead of
> primitives failing.
FWIW, I don't think we need that flag. Failing the primitive instead of
producing something that is specifically declared not to be a number in
an arithmetic computation is *always* the right thing to do. The problem
with NaNs is that they propagate. So you start with an isolated NaN as
the result of a division by an underflow number and may be able to catch
it. But you don't because it's silent and then it propagates into a
matrix because you're scaling the matrix by that number. Now you've got
a matrix full of NaNs. As you push your geometry through that matrix
everything becomes complete and utter NaN garbage. And of course, NaNs
break reflexivity, symmetry and transitivity of comparisons.
As a consequence we should never allow them to be introduced silently by
the VM. If the error handling code for some arithmetic primitive decides
that against all reasoning you'd like to produce an NaN as the result
regardless, that's fine, you have been warned. But having the VM
introduce NaNs silently is wrong, wrong, wrong.
> b) the Cog code generator needs to respect this flag and arrange that
> when in the default mode (current behavior) the machine-code arithmetic
> float primitives also fail if they produce a NaN result.
> We can then decide at a later date whether to change the primitive
> behavior to answer NaNs or not. This is also what we did in
> VisualWorks; there's an IEEE arithmetic mode and in recent releases VW's
> floating-point arithmetic will produce NaNs.
> Anyone interested in taking a look at this is very welcome. Its
> probably a week long project at most.
> On Thu, Sep 16, 2010 at 12:19 PM, Nicolas Cellier
> <nicolas.cellier.aka.nice at gmail.com
> <mailto:nicolas.cellier.aka.nice at gmail.com>> wrote:
> I mean the M7260-primitiveSmallIntegerCompareNan-Patch-nice.1.cs part,
> the rest has already been applied in COG.
> 2010/9/16 Nicolas Cellier <nicolas.cellier.aka.nice at gmail.com
> <mailto:nicolas.cellier.aka.nice at gmail.com>>:
> > I see http://bugs.squeak.org/view.php?id=7260 was not integrated in
> > COG, which was the cause of most of the Floating point failures
> in old
> > VM, but maybe it's now more complex than that ?
> > Nicolas
> > 2010/9/16 Mariano Martinez Peck <marianopeck at gmail.com
> <mailto:marianopeck at gmail.com>>:
> >> Hi Eliot. I took a Pharo 1.1.1 image (which has included the
> changes to run Cog) and I run all the tests with the build r2219
> >> And these are the results:
> >> 9768 run, 9698 passes, 53 expected failures, 15 failures, 2
> errors, 0 unexpected passes
> >> Failures:
> >> FloatTest>>#testRaisedTo
> >> MCInitializationTest>>#testWorkingCopy
> >> FloatTest>>#testReciprocal
> >> ReleaseTest>>#testUndeclared
> >> FloatTest>>#testDivide
> >> MethodContextTest>>#testClosureRestart
> >> FloatTest>>#testCloseTo
> >> FloatTest>>#testHugeIntegerCloseTo
> >> FloatTest>>#testInfinityCloseTo
> >> WeakRegistryTest>>#testFinalization
> >> PCCByLiteralsTest>>#testSwitchPrimCallOffOn
> >> AllocationTest>>#testOneGigAllocation
> >> FloatTest>>#testNaNCompare
> >> FileStreamTest>>#testPositionPastEndIsAtEnd
> >> NumberTest>>#testRaisedToIntegerWithFloats
> >> Errors:
> >> MessageTallyTest>>#testSampling1
> >> WeakSetInspectorTest>>#testSymbolTableM6812
> >> I think that most of these problems were fixed in latest
> official SqueakVM. I guess they were integrated in VMMaker in
> versions later than the one you used for Cog. Maybe you can
> integrate them and create a new version?
> >> I am not a VM expert so please if you can help us with this
> tests it would be cool.
> >> Thanks
> >> Mariano
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