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Re: "Fix" recent povray failure with -mfpmath=sse -ffast-math


Richard Henderson wrote:

But the fact remains that either the current mechanism or the
test above really ought to be valid when there are no NaNs in
the program.  I can only assume from this that PovRay actually
does generate or consume NaNs, and that using -ffast-math is
in fact invalid.

But we can't know for sure without a reduced test case.

PS: It would probably behoove PovRay to unmask floating point exceptions
such that if a NaN is generated we get a SIGFPE instead of silently doing
the wrong thing.



comis? instructions generate an INVALID OPERATION exception if they encounter a NaN. I have added a _MM_SET_EXCEPTION_MASK (0x1f00) after povray_init() to catch unordered compares, but there were no exceptions (and the rendered picture was still wrong).

Is it possible that the problem is in PR 19496?

Uros.


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