I discovered yet another issue with missing RCE during work on JDK-8324751.

At first, I thought I only had issues with getAtIndex JDK-8360204, but it also happens with get/set it seems. These may be possible duplicates!

NOTE: we already have a test integrated with JDK-8324751, so just edit that one:
test/hotspot/jtreg/compiler/loopopts/superword/TestMemorySegment_8365982.java

We see that the loop does some "Predicate RC" before unrolling, but it seems it does not manage to get all range checks at the beginning.
After unrolling 4x, it multiversions (strange!).
Then, with PreMainPost, we are doing "RangeCheck", and now the main-loop of the multiversion_fast loop does no have any rangechecks any more.

Question: why was this RangeCheck not eliminated at the beginning?
Why do we multiversion? Did we lose contact to the predicates somewhere in between?


java -XX:CompileCommand=compileonly,Test::test -XX:CompileCommand=printcompilation,Test::test -Xbatch -XX:+TraceLoopOpts Test.java


5678  111    b  4       Test::test (133 bytes)
Counted        Loop: N1971/N1969  limit_check short_running profile_predicated predicated sfpts={ 1809 }
Loop: N0/N0  has_sfpt
  Loop: N1971/N1969  limit_check short_running profile_predicated predicated sfpts={ 1809 }
Loop: N0/N0  has_sfpt
  Loop: N1971/N1969  limit_check short_running profile_predicated predicated sfpts={ 1809 }
Predicate IC   Loop: N1971/N1969  limit_check short_running profile_predicated predicated rce sfpts={ 1809 }
Predicate IC   Loop: N1971/N1969  limit_check short_running profile_predicated predicated rce sfpts={ 1809 }
Predicate IC   Loop: N1971/N1969  limit_check short_running profile_predicated predicated rce sfpts={ 1809 }
Predicate IC   Loop: N1971/N1969  limit_check short_running profile_predicated predicated rce sfpts={ 1809 }
Predicate IC   Loop: N1971/N1969  limit_check short_running profile_predicated predicated rce sfpts={ 1809 }
Predicate IC   Loop: N1971/N1969  limit_check short_running profile_predicated predicated rce sfpts={ 1809 }
Predicate IC   Loop: N1971/N1969  limit_check short_running profile_predicated predicated rce sfpts={ 1809 }
Predicate IC   Loop: N1971/N1969  limit_check short_running profile_predicated predicated rce sfpts={ 1809 }
Predicate IC   Loop: N1971/N1969  limit_check short_running profile_predicated predicated rce sfpts={ 1809 }
Predicate IC   Loop: N1971/N1969  limit_check short_running profile_predicated predicated rce sfpts={ 1809 }
Predicate IC   Loop: N1971/N1969  limit_check short_running profile_predicated predicated rce sfpts={ 1809 }
Predicate IC   Loop: N1971/N1969  limit_check short_running profile_predicated predicated rce sfpts={ 1809 }
Predicate IC   Loop: N1971/N1969  limit_check short_running profile_predicated predicated rce sfpts={ 1809 }
Predicate IC   Loop: N1971/N1969  limit_check short_running profile_predicated predicated rce sfpts={ 1809 }
Predicate IC   Loop: N1971/N1969  limit_check short_running profile_predicated predicated rce sfpts={ 1809 }
Predicate IC   Loop: N1971/N1969  limit_check short_running profile_predicated predicated rce sfpts={ 1809 }
Predicate IC   Loop: N1971/N1969  limit_check short_running profile_predicated predicated rce sfpts={ 1809 }
Predicate IC   Loop: N1971/N1969  limit_check short_running profile_predicated predicated rce sfpts={ 1809 }
Loop: N0/N0  has_sfpt
  Loop: N1971/N1969  limit_check short_running profile_predicated predicated sfpts={ 1809 }
Exceeding node budget: 0 < 62
Counted          Loop: N2328/N2322  counted [0,int),-1 (-1 iters) 
Loop: N0/N0  has_sfpt
  Loop: N2327/N2326  limit_check short_running profile_predicated predicated
    Loop: N2328/N2322  limit_check short_running profile_predicated predicated counted [0,int),-1 (-1 iters)  has_sfpt strip_mined
Predicate RC     Loop: N2328/N2322  limit_check short_running profile_predicated predicated counted [0,int),-1 (1000 iters)  has_sfpt strip_mined
Loop: N0/N0  has_sfpt
  Loop: N2327/N2326  limit_check short_running profile_predicated predicated sfpts={ 2329 }
    Loop: N2328/N2322  limit_check short_running profile_predicated predicated counted [0,int),-1 (1000 iters)  rc  has_sfpt strip_mined
PreMainPost      Loop: N2328/N2322  limit_check short_running profile_predicated predicated counted [0,int),-1 (1000 iters)  rc  has_sfpt strip_mined
Unroll 2         Loop: N2328/N2322  limit_check counted [int,int),-1 (1000 iters)  main rc  has_sfpt strip_mined
Loop: N0/N0  has_sfpt
  Loop: N2536/N2534  limit_check short_running profile_predicated predicated counted [0,int),-1 (4 iters)  pre rc 
  Loop: N2327/N2326  limit_check sfpts={ 2329 }
    Loop: N2651/N2322  limit_check counted [int,int),-2 (1000 iters)  main rc  has_sfpt strip_mined
  Loop: N2433/N2431  limit_check counted [int,int),-1 (4 iters)  post rc 
Unroll 4         Loop: N2651/N2322  limit_check counted [int,int),-2 (1000 iters)  main rc  has_sfpt rce strip_mined
Loop: N0/N0  has_sfpt
  Loop: N2536/N2534  limit_check short_running profile_predicated predicated counted [0,int),-1 (4 iters)  pre rc 
  Loop: N2327/N2326  limit_check sfpts={ 2329 }
    Loop: N2835/N2322  limit_check counted [int,int),-4 (1000 iters)  main rc  has_sfpt strip_mined
  Loop: N2433/N2431  limit_check counted [int,int),-1 (4 iters)  post rc 
Exceeding node budget: 0 < 106
Loop: N0/N0  has_sfpt
  Loop: N2536/N2534  limit_check short_running profile_predicated predicated counted [0,int),-1 (4 iters)  pre rc 
  Loop: N2327/N2326  limit_check sfpts={ 2329 }
    Loop: N2835/N2322  limit_check counted [0,int),-4 (1000 iters)  rc  has_sfpt strip_mined
  Loop: N2433/N2431  limit_check counted [int,int),-1 (4 iters)  post rc 
Multiversion     Loop: N2835/N2322  limit_check counted [0,int),-4 (1000 iters)  rc  has_sfpt rce strip_mined
PreMainPost      Loop: N2835/N2322  limit_check counted [0,int),-4 (1000 iters)  rc  multiversion_fast has_sfpt rce strip_mined
RangeCheck       Loop: N2835/N2322  limit_check counted [int,int),-4 (1000 iters)  main rc  multiversion_fast has_sfpt rce strip_mined
Loop: N0/N0  has_sfpt
  Loop: N2536/N2534  limit_check short_running profile_predicated predicated counted [0,int),-1 (4 iters)  pre rc 
  Loop: N3442/N3443  limit_check sfpts={ 3445 }
    Loop: N3427/N3438  limit_check counted [0,int),-4 (1000 iters)  rc  multiversion_delayed_slow has_sfpt strip_mined
  Loop: N3714/N3725  counted [0,int),-4 (4 iters)  pre rc  multiversion_fast
  Loop: N2327/N2326  limit_check sfpts={ 2329 }
    Loop: N2835/N2322  limit_check counted [int,int),-4 (1000 iters)  main multiversion_fast has_sfpt strip_mined
  Loop: N3570/N3581  limit_check counted [int,int),-4 (4 iters)  post rc  multiversion_fast
  Loop: N2433/N2431  limit_check counted [int,int),-1 (4 iters)  post rc 
Unroll 8         Loop: N2835/N2322  limit_check counted [int,int),-4 (1000 iters)  main multiversion_fast has_sfpt strip_mined
Loop: N0/N0  has_sfpt
  Loop: N2536/N2534  limit_check short_running profile_predicated predicated counted [0,int),-1 (4 iters)  pre rc 
  Loop: N3442/N3443  limit_check sfpts={ 3445 }
    Loop: N3427/N3438  limit_check counted [0,int),-4 (1000 iters)  rc  multiversion_delayed_slow has_sfpt strip_mined
  Loop: N3714/N3725  counted [0,int),-4 (4 iters)  pre rc  multiversion_fast
  Loop: N2327/N2326  limit_check sfpts={ 2329 }
    Loop: N4339/N2322  limit_check counted [int,int),-8 (1000 iters)  main multiversion_fast has_sfpt strip_mined
  Loop: N3570/N3581  limit_check counted [int,int),-4 (4 iters)  post rc  multiversion_fast
  Loop: N2433/N2431  limit_check counted [int,int),-1 (4 iters)  post rc 
Unroll 16         Loop: N4339/N2322  limit_check counted [int,int),-8 (1000 iters)  main multiversion_fast has_sfpt strip_mined
Loop: N0/N0  has_sfpt
  Loop: N2536/N2534  limit_check short_running profile_predicated predicated counted [0,int),-1 (4 iters)  pre rc 
  Loop: N3442/N3443  limit_check sfpts={ 3445 }
    Loop: N3427/N3438  limit_check counted [0,int),-4 (1000 iters)  rc  multiversion_delayed_slow has_sfpt strip_mined
  Loop: N3714/N3725  counted [0,int),-4 (4 iters)  pre rc  multiversion_fast
  Loop: N2327/N2326  limit_check sfpts={ 2329 }
    Loop: N4657/N2322  limit_check counted [int,int),-16 (1000 iters)  main multiversion_fast has_sfpt strip_mined
  Loop: N3570/N3581  limit_check counted [int,int),-4 (4 iters)  post rc  multiversion_fast
  Loop: N2433/N2431  limit_check counted [int,int),-1 (4 iters)  post rc 
Unroll 32         Loop: N4657/N2322  limit_check counted [int,int),-16 (1000 iters)  main multiversion_fast has_sfpt strip_mined
Loop: N0/N0  has_sfpt
  Loop: N2536/N2534  limit_check short_running profile_predicated predicated counted [0,int),-1 (4 iters)  pre rc 
  Loop: N3442/N3443  limit_check sfpts={ 3445 }
    Loop: N3427/N3438  limit_check counted [0,int),-4 (1000 iters)  rc  multiversion_delayed_slow has_sfpt strip_mined
  Loop: N3714/N3725  counted [0,int),-4 (4 iters)  pre rc  multiversion_fast
  Loop: N2327/N2326  limit_check sfpts={ 2329 }
    Loop: N5064/N2322  limit_check counted [int,int),-32 (1000 iters)  main multiversion_fast has_sfpt strip_mined
  Loop: N3570/N3581  limit_check counted [int,int),-4 (4 iters)  post rc  multiversion_fast
  Loop: N2433/N2431  limit_check counted [int,int),-1 (4 iters)  post rc 
Loop: N0/N0  has_sfpt
  Loop: N2536/N2534  limit_check short_running profile_predicated predicated counted [0,int),-1 (4 iters)  pre rc 
  Loop: N3442/N3443  limit_check sfpts={ 3445 }
    Loop: N3427/N3438  limit_check counted [0,int),-4 (1000 iters)  rc  multiversion_delayed_slow has_sfpt strip_mined
  Loop: N3714/N3725  counted [0,int),-4 (4 iters)  pre rc  multiversion_fast
  Loop: N2327/N2326  limit_check sfpts={ 2329 }
    Loop: N5064/N2322  limit_check counted [int,int),-32 (1000 iters)  main multiversion_fast has_sfpt strip_mined
  Loop: N3570/N3581  limit_check counted [int,int),-4 (4 iters)  post rc  multiversion_fast
  Loop: N2433/N2431  limit_check counted [int,int),-1 (4 iters)  post rc 
PredicatesOff
Loop: N0/N0  has_sfpt
  Loop: N2536/N2534  short_running predicated counted [0,int),-1 (4 iters)  pre rc 
  Loop: N3442/N3443  limit_check sfpts={ 3445 }
    Loop: N3427/N3438  limit_check counted [0,int),-4 (1000 iters)  rc  multiversion_delayed_slow has_sfpt strip_mined
  Loop: N3714/N3725  counted [0,int),-4 (4 iters)  pre rc  multiversion_fast
  Loop: N2327/N2326  limit_check sfpts={ 2329 }
    Loop: N5064/N2322  limit_check counted [int,int),-32 (1000 iters)  main multiversion_fast has_sfpt strip_mined
  Loop: N3570/N3581  limit_check counted [int,int),-4 (4 iters)  post rc  multiversion_fast
  Loop: N2433/N2431  limit_check counted [int,int),-1 (4 iters)  post rc