[LLVMdev] Disable loop unroll pass
shuxin.llvm at gmail.com
Thu Nov 22 10:55:12 PST 2012
> I appreciate your feed-back. Could you give an example where building
> a hw loop is not appropriate for your target?
In my case, unrolling and hw loop is orthogonal. So long as a loop is
countable & size dosen't exceeds
some threshold, it can be converted into a hw loop. So loop is desirable
to be unrolled.
One benefit of unrolling is to exposed inter-iteration redundancies, and
the downstream redundancy
elimination can *easily* take care them. We would otherwise have to
resort to iter-iteration
redundancy eliminators to remove such redundancies in a *HARD* way,
As far as I know, LLVM doesn't have iter-iteration redundancy
elimination (like predictive commoning),
and it dosen't have scalar replacement to promote subscript variable to
register (i.e the 2nd
load in a[i]... a[i-n] is load from register; GVN can promote a[i-n] to
register only if n==1).
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