[RELAY]sch and compute for reduce ops

[siju-samuel]

#2051
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[jroesch]

Looks good to me once CI passes.

[siju-samuel]

======================================================================
ERROR: test_top_level4.test_reduce
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/usr/local/lib/python2.7/dist-packages/nose/case.py", line 197, in runTest
    self.test(*self.arg)
  File "/workspace/nnvm/tests/python/compiler/test_top_level4.py", line 98, in test_reduce
    verify_reduce((4, 4, 3), np.sum, sym.sum)
  File "/workspace/nnvm/tests/python/compiler/test_top_level4.py", line 56, in verify_reduce
    verify_reduce_explicit(dshape, data, result, fsym, oshape=oshape, otype=otype, **kwargs)
  File "/workspace/nnvm/tests/python/compiler/test_top_level4.py", line 37, in verify_reduce_explicit
    graph, lib, _ = nnvm.compiler.build(y, target, {"x": dshape})
  File "/workspace/nnvm/python/nnvm/compiler/build_module.py", line 305, in build
    graph = graph.apply("GraphCompile")
  File "/workspace/nnvm/python/nnvm/graph.py", line 234, in apply
    check_call(_LIB.NNGraphApplyPasses(self.handle, npass, cpass, ctypes.byref(ghandle)))
  File "/workspace/nnvm/python/nnvm/_base.py", line 75, in check_call
    raise NNVMError(py_str(_LIB.NNGetLastError()))
NNVMError: [12:10:58] /workspace/nnvm/src/compiler/compile_engine.cc:212: Check failed: out[i].ndim() == out_info[i].ndim() (0 vs. 1) sum

Any idea why nnvm/tests/python/compiler/test_top_level4.py script is failing in CI?

[tqchen]

This is certainly the shortest line of addition to implement the feature. But not necessarily the fastest to run. Note that the reduction in topi already supports negative index. So we don't need to handle negative index here, the only thing we need to handle is exclude, we can use another function GetExcludeAxes to get the other axes and return them as Array when there is exclude

[tqchen]

with target:

[tqchen]

see the compute impl in #2163 that reflects the commend, the test-cases are still helpful and we would like to bring it in after 2163

[tqchen]

Thanks @siju-samuel @jroesch this is merged