[Bugfix] Fixed div by zero core dump. Fixed rounding intrinsics on int crash

[dpankratz]

Div by zero crash

I found and fixed 2 instances where a divide by zero could be evaluated in const_fold causing a Python core dump. For example tir.const(2) % 0.

Rounding intrinsics

When I tried to use llvm intrinsics on integers I found all of them but popcount result in an error analogous to:

TVMError: LLVM module verification failed with the following errors: 
Intrinsic has incorrect return type!
i32 (i32)* @llvm.floor.i32

To fix this for trunc,floor,ceil,nearbyint,round it is sufficient to return the int expr and avoid the call altogether.

Other intrinsics

I was looking at fixing the above crash for other intrinsics (sin,cos,atan,tan,tanh,sigmoid,log,erf,exp,sqrt,rsqrt) by restricting their usage to floating point numbers. However applying exp and sqrt to bool type seems to be relied on in this test:

https://github.com/apache/incubator-tvm/blob/master/topi/tests/python/test_topi_reduce.py#L51

Evaluating this line for a bool is equivalent to a tautology which makes me suspect it is not intended. If the reviewer(s) agree that these intrinsics should not be applied to ints, then I can add a front-end checks on the instrinsics to this PR and fix the tests.

I would appreciate a review!

@tqchen

[tqchen]

LTGM, @dpankratz can you please rebase against the master

[tqchen]

seems that the rebase mess up with the commit history someone, can you try to re-apply the changes on top of the master? Try

git rebase --onto upstream/master HEAD~1

This takes your last commit and rebase it on top of the master

[dpankratz]

@tqchen Let me know if that looks good. Thanks for your advice with that command!

[tqchen]

Thanks @dpankratz !