[PATCH] D94074: [AArch64][SVE] Remove chains of unnecessary SVE reinterpret intrinsics

[Joe Ellis via Phabricator via llvm-commits]

joechrisellis added inline comments.


================
Comment at: llvm/test/CodeGen/AArch64/sve-intrinsic-opts-reinterpret.ll:84
+; work as the first two.
+define <vscale x 4 x i1> @reinterpret_test_partial_chain(<vscale x 2 x i1> %a) {
+; OPT-LABEL: @reinterpret_test_partial_chain(
----------------
david-arm wrote:
> david-arm wrote:
> > If you create a test with similar to this, but with "<vscale x 2 x i1> %a" is there a bug? From your algorithm above it looks like EarliestRemoval would be "%2 tail call ...", but we'd keep iterating Cursor until we get to "%a". If I've understood your algorithm correctly won't that mean we end up deleting %1 and %2 and end up with this?
> > 
> > define <vscale x 4 x i1> @reinterpret_test_partial_chain(<vscale x 8 x i1> %a) {
> >   ret <vscale x 4 x i1> %2;
> > }
> > 
> Sorry, I meant create a test similar to this, but with "<vscale x 8 x i1> %a"!!
Hi @david-arm, just tested the algorithm with the following code:

```
define <vscale x 4 x i1> @foo(<vscale x 8 x i1> %a) {
  %1 = tail call <vscale x 16 x i1> @llvm.aarch64.sve.convert.to.svbool.nxv8i1(<vscale x 8 x i1> %a)
  %2 = tail call <vscale x 4 x i1> @llvm.aarch64.sve.convert.from.svbool.nxv4i1(<vscale x 16 x i1> %1)
  %3 = tail call <vscale x 16 x i1> @llvm.aarch64.sve.convert.to.svbool.nxv4i1(<vscale x 4 x i1> %2)
  %4 = tail call <vscale x 4 x i1> @llvm.aarch64.sve.convert.from.svbool.nxv4i1(<vscale x 16 x i1> %3)
  ret <vscale x 4 x i1> %4
}
```

And got the following output:

```
define <vscale x 4 x i1> @foo(<vscale x 8 x i1> %a) #1 {
  %1 = tail call <vscale x 16 x i1> @llvm.aarch64.sve.convert.to.svbool.nxv8i1(<vscale x 8 x i1> %a)
  %2 = tail call <vscale x 4 x i1> @llvm.aarch64.sve.convert.from.svbool.nxv4i1(<vscale x 16 x i1> %1)
  ret <vscale x 4 x i1> %2
}
```

This makes sense to me, although maybe I haven't fed the pass the same code that you were thinking of?


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https://reviews.llvm.org/D94074