[PATCH] D140676: [AArch64] `LowerZERO_EXTEND_VECTOR_INREG()`: recursively apply `zip1` until done

Mon Jan 2 10:44:50 PST 2023

lebedev.ri marked 2 inline comments as done.
lebedev.ri added inline comments.

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Comment at: llvm/test/CodeGen/AArch64/zext-to-tbl.ll:1025
+; CHECK-NEXT:    zip1.16b v1, v1, v0
+; CHECK-NEXT:    zip1.8h v1, v1, v0
 ; CHECK-NEXT:    str q1, [x1], #64
----------------
fhahn wrote:
> lebedev.ri wrote:
> > fhahn wrote:
> > > lebedev.ri wrote:
> > > > fhahn wrote:
> > > > > I think that for this lowering is slightly worse in general for CPUs that have efficient implementations of `tbl`, as `tbl` results in shorter dependency chains than having 2 `zip1`, with one depending on the other. The `tbl` lowering is only used in loops, when the load from the constant pool is hoisted outside the loop. 
> > > > Note: i personally do not care what happens here, i'm only asking because this comes up
> > > > as a "regression" in further patches (D140677 e.g.), so i'm wondering if this needs to be dealt with.
> > > > 
> > > Yeah, IMO this is a regression that should be avoided (at least in loops)
> > Err, i'm still confused. You are saying this patch is not needed, correct? :)
> Yep, it should not be needed.
Cheers, thank you.

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D140676/new/

https://reviews.llvm.org/D140676