Reduce memory usage of benchmarks and of merge sort

[ChaiTRex]

Summary with benchmark results

Benchmarking merge sort with a vector size of 250,000,000, timing results are unaffected by these commits. However, the benchmarks use:

about 9.32 GiB before these commits

$ time -v dist/build/simple-bench/simple-bench -A MergeSort -n 250000000
Testing: merge sort
Random             : 105.641547237 seconds
Sorted             : 43.755033358 seconds
Reverse-sorted     : 47.927451066 seconds
Random duplicates  : 94.516762071 seconds
Median killer      : 55.749034796 seconds
	Command being timed: "dist/build/simple-bench/simple-bench -A MergeSort -n 250000000"
	User time (seconds): 355.31
	System time (seconds): 4.27
	Percent of CPU this job got: 99%
	Elapsed (wall clock) time (h:mm:ss or m:ss): 5:59.68
	Average shared text size (kbytes): 0
	Average unshared data size (kbytes): 0
	Average stack size (kbytes): 0
	Average total size (kbytes): 0
	Maximum resident set size (kbytes): 9772512
	Average resident set size (kbytes): 0
	Major (requiring I/O) page faults: 0
	Minor (reclaiming a frame) page faults: 2442312
	Voluntary context switches: 1
	Involuntary context switches: 5833
	Swaps: 0
	File system inputs: 0
	File system outputs: 0
	Socket messages sent: 0
	Socket messages received: 0
	Signals delivered: 0
	Page size (bytes): 4096
	Exit status: 0

$ time -v dist/build/simple-bench/simple-bench -A MergeSort -n 250000000
Testing: merge sort
Random             : 102.0173054 seconds
Sorted             : 43.215281981 seconds
Reverse-sorted     : 46.977218873 seconds
Random duplicates  : 90.620823144 seconds
Median killer      : 54.175290449 seconds
	Command being timed: "dist/build/simple-bench/simple-bench -A MergeSort -n 250000000"
	User time (seconds): 344.88
	System time (seconds): 3.93
	Percent of CPU this job got: 99%
	Elapsed (wall clock) time (h:mm:ss or m:ss): 5:48.85
	Average shared text size (kbytes): 0
	Average unshared data size (kbytes): 0
	Average stack size (kbytes): 0
	Average total size (kbytes): 0
	Maximum resident set size (kbytes): 9772684
	Average resident set size (kbytes): 0
	Major (requiring I/O) page faults: 0
	Minor (reclaiming a frame) page faults: 2442312
	Voluntary context switches: 1
	Involuntary context switches: 1626
	Swaps: 0
	File system inputs: 0
	File system outputs: 0
	Socket messages sent: 0
	Socket messages received: 0
	Signals delivered: 0
	Page size (bytes): 4096
	Exit status: 0

about 7.45 GiB after the first commit

$ time -v dist/build/simple-bench/simple-bench -A MergeSort -n 250000000
Testing: merge sort
Random             : 102.570755197 seconds
Sorted             : 43.153803419 seconds
Reverse-sorted     : 48.570614044 seconds
Random duplicates  : 93.463369144 seconds
Median killer      : 54.63930903 seconds
	Command being timed: "dist/build/simple-bench/simple-bench -A MergeSort -n 250000000"
	User time (seconds): 349.71
	System time (seconds): 3.49
	Percent of CPU this job got: 99%
	Elapsed (wall clock) time (h:mm:ss or m:ss): 5:53.24
	Average shared text size (kbytes): 0
	Average unshared data size (kbytes): 0
	Average stack size (kbytes): 0
	Average total size (kbytes): 0
	Maximum resident set size (kbytes): 7819640
	Average resident set size (kbytes): 0
	Major (requiring I/O) page faults: 0
	Minor (reclaiming a frame) page faults: 1954059
	Voluntary context switches: 1
	Involuntary context switches: 2245
	Swaps: 0
	File system inputs: 0
	File system outputs: 0
	Socket messages sent: 0
	Socket messages received: 0
	Signals delivered: 0
	Page size (bytes): 4096
	Exit status: 0

$ time -v dist/build/simple-bench/simple-bench -A MergeSort -n 250000000
Testing: merge sort
Random             : 104.736320866 seconds
Sorted             : 44.565925792 seconds
Reverse-sorted     : 49.598375232 seconds
Random duplicates  : 92.925600618 seconds
Median killer      : 56.065786839 seconds
	Command being timed: "dist/build/simple-bench/simple-bench -A MergeSort -n 250000000"
	User time (seconds): 355.34
	System time (seconds): 3.49
	Percent of CPU this job got: 99%
	Elapsed (wall clock) time (h:mm:ss or m:ss): 5:58.87
	Average shared text size (kbytes): 0
	Average unshared data size (kbytes): 0
	Average stack size (kbytes): 0
	Average total size (kbytes): 0
	Maximum resident set size (kbytes): 7819500
	Average resident set size (kbytes): 0
	Major (requiring I/O) page faults: 0
	Minor (reclaiming a frame) page faults: 1954058
	Voluntary context switches: 1
	Involuntary context switches: 2174
	Swaps: 0
	File system inputs: 0
	File system outputs: 0
	Socket messages sent: 0
	Socket messages received: 0
	Signals delivered: 0
	Page size (bytes): 4096
	Exit status: 0

about 5.59 GiB after both commits

$ time -v dist/build/simple-bench/simple-bench -A MergeSort -n 250000000
Testing: merge sort
Random             : 100.119498798 seconds
Sorted             : 44.544652572 seconds
Reverse-sorted     : 47.439132265 seconds
Random duplicates  : 89.077430416 seconds
Median killer      : 52.108055876 seconds
	Command being timed: "dist/build/simple-bench/simple-bench -A MergeSort -n 250000000"
	User time (seconds): 341.05
	System time (seconds): 2.96
	Percent of CPU this job got: 99%
	Elapsed (wall clock) time (h:mm:ss or m:ss): 5:44.05
	Average shared text size (kbytes): 0
	Average unshared data size (kbytes): 0
	Average stack size (kbytes): 0
	Average total size (kbytes): 0
	Maximum resident set size (kbytes): 5866496
	Average resident set size (kbytes): 0
	Major (requiring I/O) page faults: 0
	Minor (reclaiming a frame) page faults: 1465782
	Voluntary context switches: 1
	Involuntary context switches: 3009
	Swaps: 0
	File system inputs: 0
	File system outputs: 0
	Socket messages sent: 0
	Socket messages received: 0
	Signals delivered: 0
	Page size (bytes): 4096
	Exit status: 0

$ time -v dist/build/simple-bench/simple-bench -A MergeSort -n 250000000
Testing: merge sort
Random             : 99.84921236 seconds
Sorted             : 40.872955826 seconds
Reverse-sorted     : 46.306745789 seconds
Random duplicates  : 89.254555669 seconds
Median killer      : 53.497425148 seconds
	Command being timed: "dist/build/simple-bench/simple-bench -A MergeSort -n 250000000"
	User time (seconds): 337.80
	System time (seconds): 2.78
	Percent of CPU this job got: 99%
	Elapsed (wall clock) time (h:mm:ss or m:ss): 5:40.62
	Average shared text size (kbytes): 0
	Average unshared data size (kbytes): 0
	Average stack size (kbytes): 0
	Average total size (kbytes): 0
	Maximum resident set size (kbytes): 5866352
	Average resident set size (kbytes): 0
	Major (requiring I/O) page faults: 0
	Minor (reclaiming a frame) page faults: 1465779
	Voluntary context switches: 1
	Involuntary context switches: 3351
	Swaps: 0
	File system inputs: 0
	File system outputs: 0
	Socket messages sent: 0
	Socket messages received: 0
	Signals delivered: 0
	Page size (bytes): 4096
	Exit status: 0

This also reduces merge sort's memory usage outside of benchmarks.

Compiling and testing

I'm unsure of whether or not the BoundsChecks, UnsafeChecks, and InternalChecks flags actually do anything, as I didn't use them with cabal install vector. At any rate, all tests passed in all three cases above.

$ cabal configure -O2 --flags="BoundsChecks UnsafeChecks InternalChecks bench properties llvm" --enable-benchmarks --enable-tests
Resolving dependencies...
Configuring vector-algorithms-0.8.0.0...

$ cabal build --ghc-options="-fforce-recomp -O2 -fllvm -optlo -O3 -optlc -O3"
Preprocessing library for vector-algorithms-0.8.0.0..
Building library for vector-algorithms-0.8.0.0..
[ 1 of 10] Compiling Data.Vector.Algorithms.Common ( src/Data/Vector/Algorithms/Common.hs, dist/build/Data/Vector/Algorithms/Common.o )
⋮
[2 of 2] Compiling Main             ( bench/simple/Main.hs, dist/build/simple-bench/simple-bench-tmp/Main.o )
Linking dist/build/simple-bench/simple-bench ...

$ dist/build/properties/properties
Int tests:
+++ OK, passed 1000 tests (100.0% introsort).
⋮
+++ OK, passed 1 tests (100% flagsort empty).

[erikd]

Nice!