[PATCH] D148647: [RISCV] Fix interleave crash on unary interleaves

[Luke Lau via Phabricator via llvm-commits]

luke added inline comments.


================
Comment at: llvm/lib/Target/RISCV/RISCVISelLowering.cpp:3294
 
+  // If both elements of the even and odd vector are smaller than the size of
+  // the VT, then it's an unary interleave like:  
----------------
craig.topper wrote:
> I wonder if the fix should be
> 
> if (EvenSrc % (NumElts / 2) != 0 || OddSrc % (NumElts /2) != 0)
That works for the first two cases mentioned but then it seems to miss the interleave in this case:

```
; This interleaves the first 2 elements of a vector in opposite order. With
; undefs for the remaining elements. We use to miscompile this.
define <4 x i8> @unary_interleave_10uu_v4i8(<4 x i8> %x) {
  %a = shufflevector <4 x i8> %x, <4 x i8> poison, <4 x i32> <i32 1, i32 0, i32 undef, i32 undef>
  ret <4 x i8> %a
}
```

I noticed we also probably want to support non-multiple-of-numelts offsets like this:
```
shufflevector <4 x i32> %x, <4 x i32> %y, <4 x i32> <i32 0, i32 5, i32 1, i32 6>
```

I've updated the patch to check the range given we know the start indices and size of each vector being interleaved, but there's probably a more elegant way of expressing this that I'm missing


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D148647/new/

https://reviews.llvm.org/D148647