[REVIEW] Move template param to member var to improve compile of hash/groupby.cu

[davidwendt]

The compile time/size of cpp/src/groupby/hash/groupby.cu is one of the top offenders for building libcudf.

Current top 5 slowest compiles:

1813479 CMakeFiles/cudf_base.dir/src/sort/sort.cu.o
1805726 CMakeFiles/cudf_base.dir/src/sort/stable_sort.cu.o
1091904 CMakeFiles/cudf_base.dir/src/stream_compaction/drop_duplicates.cu.o
 979061 CMakeFiles/cudf_base.dir/src/groupby/hash/groupby.cu.o  <----
 685116 CMakeFiles/cudf_join.dir/src/join/semi_join.cu.o
...

The two sort.cu files may be improved in a later PR. The drop_duplicates.cu is being addressed in #6822

The simple change here is to compute_single_pass_aggs functor defined here:

cudf/cpp/src/groupby/hash/groupby_kernels.cuh

Lines 65 to 66 in 591bead

	template <bool skip_rows_with_nulls, typename Map>
	struct compute_single_pass_aggs {

The skip_rows_with_nulls template parameter is set to avoid calling (and inlining) cudf::bit_is_set(). This function is minimal compared to the cudf::detail::aggregate_row function that must be inlined twice to accommodate this template parameter. Simply changing this to a member variable means we still do not incur an extra call to cudf::bit_is_set() when appropriate but also means we generate half as much device code for this specific function. The cudf::detail::aggregate_row code is quite significant.

This change reduces the compile time for hash/groupby.cu from 16 minutes to 9 minutes. This moves it out of the top 5 (for now). This also reduces the size of the libcudf_base.so by ~5MB.

There is no functional changes to any logic. The gbenchmark/GROUPBY_BENCH shows no change in performance.

[davidwendt]

Error 137 is "out of memory"

[codecov]

Codecov Report

Merging #6835 (57a6f5b) into branch-0.17 (45bd967) will not change coverage.
The diff coverage is n/a.

@@             Coverage Diff              @@
##           branch-0.17    #6835   +/-   ##
============================================
  Coverage        81.94%   81.94%           
============================================
  Files               96       96           
  Lines            16164    16164           
============================================
  Hits             13246    13246           
  Misses            2918     2918           

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[harrism]

@nvdbaranec is out this week so removing his review request.

[davidwendt]

rerun tests