[PATCH] D38417: [test-suite] Adding HACCKernels app

[Sanjay Patel via Phabricator via llvm-commits]

spatel added inline comments.


================
Comment at: MultiSource/Benchmarks/DOE-ProxyApps-C++/HACCKernels/Makefile:4
+PROG     = HACCKernels
+FP_TOLERANCE = 0.00001
+CXXFLAGS = -ffast-math -DVERIFICATION_OUTPUT_ONLY=ON
----------------
hfinkel wrote:
> spatel wrote:
> > That's not big enough? We're seeing a 0.001 difference in the output string. Is that wiggle acceptable for this program? How high can we go before we decide the result is bogus?
> > 
> > You can reproduce this locally if you have at least a Sandybridge to test on. Ie, if you specify -march=nehalem (or nothing), you should see "689.584" in the output, but if you specify -march=sandybridge, you should see "689.585". 
> > 
> > I don't know what underlying transforms cause that difference, but that seems like a reasonable error for -ffast-math.
> > 
> > That's not big enough? We're seeing a 0.001 difference in the output string. Is that wiggle acceptable for this program? How high can we go before we decide the result is bogus?
> 
> Why not? It's a relative tolerance.  (We have FP_ABSTOLERANCE for setting the absolute tolerance).
> 
> In any case, the changes generally come from the inverse sqrt approximation. I think we should set this to not much more than needed for observed divergence.
> 
> Brian, were you able to confirm that this tolerance is sufficient?
Ah, sorry - I missed that this was relative. In that case, it should be ok.


https://reviews.llvm.org/D38417