Use the Builder patch for xhtml

[parsonsmatt]

This PR uses the Builder patch to the xhtml library.

Performance comparison was done in a similar manner to the CPS WriterT patch, notes on the xhtml PR.

tl;dr:

• 12% reduction in memory use for the entire Haddock run
• 48% reduction in time for the ppHtml phase

While it seems kinda funny to care too much about "oh wow 600ms to 300ms wow wow", we've got some big re-export modules at work that currently take 33 seconds to generate, and ppHtml allocates over 800GB.

EDIT:

Correctness

OK, I've tested the Haddock generation by building haddock with this patch and with the ghc-9.4 branch. The generated HTML is identical, as tested by diff.

Performance

This time I'm using persistent instead of persistent-test because it has fewer steps to get perf output from.

Haddock ghc-9.4

This is built using haddock on the ghc-9.4 branch.

ppHtml: alloc=1134416896 time=380.667
  15,979,133,408 bytes allocated in the heap
   2,437,895,544 bytes copied during GC
     238,259,312 bytes maximum residency (15 sample(s))
       5,391,248 bytes maximum slop
             554 MiB total memory in use (0 MB lost due to fragmentation)

                                     Tot time (elapsed)  Avg pause  Max pause
  Gen  0      3797 colls,     0 par    1.224s   1.226s     0.0003s    0.0031s
  Gen  1        15 colls,     0 par    0.875s   0.876s     0.0584s    0.1627s

  TASKS: 5 (1 bound, 4 peak workers (4 total), using -N1)

  SPARKS: 0 (0 converted, 0 overflowed, 0 dud, 0 GC'd, 0 fizzled)

  INIT    time    0.001s  (  0.000s elapsed)
  MUT     time    4.660s  (  5.192s elapsed)
  GC      time    2.099s  (  2.101s elapsed)
  EXIT    time    0.001s  (  0.007s elapsed)
  Total   time    6.761s  (  7.300s elapsed)

  Alloc rate    3,428,870,682 bytes per MUT second

  Productivity  68.9% of total user, 71.1% of total elapsed

Documentation created:
/home/matt/Projects/persistent/dist-newstyle/build/x86_64-linux/ghc-9.4.3/persistent-2.14.4.3/doc/html/persistent/index.html

• HTML allocations: 1134 MB
• HTML time: 380 ms
• Total Memory: 554 MB
• Total Allocated: 16.0 GB
• Max residency: 238 MB
• Total Time: 10.888 s

xhtml Builder

ppHtml: alloc=1140800792 time=197.762
  15,973,532,640 bytes allocated in the heap
   2,222,376,616 bytes copied during GC
     195,984,808 bytes maximum residency (14 sample(s))
       5,124,696 bytes maximum slop
             466 MiB total memory in use (0 MB lost due to fragmentation)

                                     Tot time (elapsed)  Avg pause  Max pause
  Gen  0      3727 colls,     0 par    1.203s   1.205s     0.0003s    0.0038s
  Gen  1        14 colls,     0 par    0.662s   0.662s     0.0473s    0.1180s

  TASKS: 5 (1 bound, 4 peak workers (4 total), using -N1)

  SPARKS: 0 (0 converted, 0 overflowed, 0 dud, 0 GC'd, 0 fizzled)

  INIT    time    0.001s  (  0.000s elapsed)
  MUT     time    4.659s  (  5.183s elapsed)
  GC      time    1.865s  (  1.867s elapsed)
  EXIT    time    0.001s  (  0.010s elapsed)
  Total   time    6.526s  (  7.060s elapsed)

  Alloc rate    3,428,220,794 bytes per MUT second

  Productivity  71.4% of total user, 73.4% of total elapsed

Documentation created:
/home/matt/Projects/persistent/dist-newstyle/build/x86_64-linux/ghc-9.4.3/persistent-2.14.4.3/doc/html/persistent/index.html

Log printed to dist-newstyle/haddock-logs/13:04_2022-04-21_haddock-builder.txt
Used haddock: /home/matt/.cabal/bin/haddock-builder

• HTML allocations: 1141 MB
• HTML time: 198 ms
• Total Memory: 466 MB
• Total Allocated: 16.0 GB
• Max residency: 195 MB
• Total Time: 6.526s s

Final Performance Comparison:

Comparing these figures, we have:

	Haddock Head	xhtml Builder	Absolute Difference	Relative Change
HTML allocations	1134 MB	1141 MB	+7 MB	0.6% worse
HTML time:	380 ms	198 ms	-182 ms	47.9% improvement
Total Memory:	554 MB	466 MB	-88 MB	15.9% improvement
Total Allocated:	16.0 GB	16.0 GB	0	No change
Max residency:	238 MB	195 MB	-43 MB	18.1% improvement
Total Time:	10.88 s	6.526s s	-4.354 s	40% improvement

Pretty pleased with these results.

[parsonsmatt]

I can't reproduce the performance, and when checking lately, I can't get this patch to be faster, at all. Going to close this out until I can figure out WTF is going on.