SuperWordLoopUnrollAnalysis and loop unrolling

[Andrew Haley]

If I set SuperWordLoopUnrollAnalysis=true, then AArch64 C2 stops after
unrolling a simple loop 4 times.  If I set
SuperWordLoopUnrollAnalysis=false, it stops after unrolling 16 times.
Why is is that SuperWordLoopUnrollAnalysis limits unrolling in this
way?

The info says
"Map number of unrolls for main loop via Superword Level Parallelism
analysis" but that doesn't help me very much.  Only AArch64 and x86
set this option.

Thanks,

Andrew.