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Floating Point Exception in vectorized pow function

gn164
Beginner
156 Views

 

Hi,

The following code fails with a Floating Point (Inavlid) Exception in __svml_powf4_l9 ()
 

      program powtest

          real s(1601)
          real power
          integer iz
          integer nz
          real dz
          character*16 out
          integer i

          power = 2.0
          nz = 1601
          dz = 5

          i = ieee_flags('set', 'exception', 'invalid', out)    !

          do iz = 1, nz
              z = (iz-1)*dz*.005
              s(iz) = z**power
          enddo

          print * , maxval(s)

      end

My processor is a Intel(R) Xeon(R) CPU E3-1240 v3 on Debian GNU/Linux 9.4

The FPE goes away if I compile with -fp-model consistent that looks like it is preventing the loop from being vectorized.

LOOP BEGIN at pow.f90(21,11)
   remark #15527: loop was not vectorized: function call to powf cannot be vectorized   [ pow.f90(23,24) ]
LOOP END

Or if I pass the -fpe0 flag to the compiler. This has the same effect for a different reason:

 remark #15335: loop was not vectorized: vectorization possible but seems inefficient. Use vector always directive or -vec-threshold0 to override

It looks to me that something goes wrong with the vectorized version of the pow function. Any ideas?

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3 Replies
Ron_Green
Moderator
156 Views

I can reproduce what you see in the 19.0.0, 19.0.1, and 19.0.2 compilers.  It seems fixed in 19.0.3 which is 2019 Update 3.  

what version of the compiler are you using?

gn164
Beginner
156 Views

Greetings Ronald,

I was using 18.0.5 but can confirm that the problem is fixed in 19.0.3. Thanks a lot for that.

I am a bit surprised though that there was a bug in svml in such a fundamental computation and how this has endured so many version updates.

If you could share some more details on what was the problem I would be curious.

 

 

 

 

gn164
Beginner
156 Views

Hi Ronald,

I am seeing similar issue in log function  _svml_clogf4_l9 () that seems to persist in 19.0.3

Can this be looked into.

 

 

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