RFR: 8320448: Accelerate IndexOf using AVX2 [v26]

[Scott Gibbons]

> Re-write the IndexOf code without the use of the pcmpestri instruction, only using AVX2 instructions.  This change accelerates String.IndexOf on average 1.3x for AVX2.  The benchmark numbers:
> 
> 
> Benchmark	                                               Score		Latest		
> StringIndexOf.advancedWithMediumSub   343.573		317.934		0.925375393x
> StringIndexOf.advancedWithShortSub1	  1039.081		1053.96		1.014319384x
> StringIndexOf.advancedWithShortSub2	      55.828		110.541		1.980027943x
> StringIndexOf.constantPattern	                9.361		11.906		1.271872663x
> StringIndexOf.searchCharLongSuccess	        4.216		4.218		1.000474383x
> StringIndexOf.searchCharMediumSuccess	3.133		3.216		1.02649218x
> StringIndexOf.searchCharShortSuccess	3.76		        3.761		1.000265957x
> StringIndexOf.success	                                9.186		9.713		1.057369911x
> StringIndexOf.successBig	                      14.341		46.343		3.231504079x
> StringIndexOfChar.latin1_AVX2_String	  6220.918		12154.52		1.953814533x
> StringIndexOfChar.latin1_AVX2_char	  5503.556		5540.044		1.006629895x
> StringIndexOfChar.latin1_SSE4_String	  6978.854		6818.689		0.977049957x
> StringIndexOfChar.latin1_SSE4_char	  5657.499		5474.624		0.967675646x
> StringIndexOfChar.latin1_Short_String	  7132.541		6863.359		0.962260014x
> StringIndexOfChar.latin1_Short_char	16013.389	      16162.437		1.009307711x
> StringIndexOfChar.latin1_mixed_String	  7386.123	      14771.622		1.999915517x
> StringIndexOfChar.latin1_mixed_char	  9901.671		9782.245		0.987938803

Scott Gibbons has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 58 commits:

 - Merge branch 'openjdk:master' into indexof
 - un-helper-ize preload_needle_helper; try fix for macos build
 - Added header file
 - Adding exhaustive test
 - Added comments; move n-k<32 code up a level
 - Fixed CI compiles; re-factor UL processing
 - Addressing lots of comments.  Interim commit.
 - Rearrange; add lambdas for clarity
 - Merge remote-tracking branch 'origin/master' into indexof
 - Move arrays_equals back to c2_MacroAssembler
 - ... and 48 more: https://git.openjdk.org/jdk/compare/37c47785...f4eefe1a

-------------

Changes: https://git.openjdk.org/jdk/pull/16753/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=16753&range=25
  Stats: 4303 lines in 16 files changed: 4140 ins; 26 del; 137 mod
  Patch: https://git.openjdk.org/jdk/pull/16753.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16753/head:pull/16753

PR: https://git.openjdk.org/jdk/pull/16753