[PATCH] D91362: [SelectionDAG] Add llvm.vector.{extract,insert} intrinsics

[Cameron McInally via Phabricator via llvm-commits]

cameron.mcinally added inline comments.


================
Comment at: llvm/docs/LangRef.rst:15995
+      declare <4 x float> @llvm.vector.insert.v4f32(<4 x float> %subvec, <4 x float> %vec, i64 %idx)
+      declare <2 x double> @llvm.vector.insert.v2f64(<2 x double> %subvec, <2 x double> %vec, i64 %idx)
+
----------------
sdesmalen wrote:
> Can you add/change the example for inserting a fixed-width vector into a scalable vector. That is one of the main reasons for adding this intrinsic.
This caught me off guard. What are the semantics of:

```
declare <4 x float> @llvm.vector.insert.v4f32(<4 x float> %subvec, <4 x float> %vec, i64 %idx)
```

Is that a full vector copy? I would have expected the subvector VL to be strictly less than the destination VL. E.g.:

```
declare <4 x float> @llvm.vector.insert.v2f32.v4f32(<2 x float> %subvec, <4 x float> %vec, i64 %idx)
```



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