[PATCH] D125747: [RISCV] Enable scalable vectorization by default for RVV

[Philip Reames via Phabricator via llvm-commits]

reames added inline comments.


================
Comment at: llvm/test/Transforms/LoopVectorize/RISCV/unroll-in-loop-vectorizer.ll:6
 ;
 define void @small_loop(i32* nocapture %inArray, i32 %size) nounwind {
 ; CHECK-LABEL: @small_loop(
----------------
craig.topper wrote:
> reames wrote:
> > reames wrote:
> > > As an aside, I took a look at the assembly for this example.  Th codegen for the vector loop ends up being less than great.  For instance:
> > > * We have a extend trapped in the loop for some reason
> > > * We rerun vsetvli on every iteration (despite it producing a fixed result)
> > > * We have a rem in the vector preheader.  That's rather expensive.  (Well, actually, we end up with a *libcall* because the attributes don't include +m, but I ignored that.)
> > To be fair, the first two issues also exist with fixed length vectorization of the same example.  
> What kind of extend?
zext - it looks easily removable, I'm surprised to see it after O2.  This shouldn't be a hard fix.  It appears in both vector and scalar loops.  


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https://reviews.llvm.org/D125747