[llvm] [InterleavedAccess] Construct interleaved access store with shuffles (PR #164000)

[Rajveer Singh Bharadwaj via llvm-commits]

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@@ -18173,6 +18180,135 @@ bool AArch64TargetLowering::lowerInterleavedStore(Instruction *Store,
   return true;
 }
 
+/// If the interleaved vector elements are greter than supported MaxFactor
+/// then, interleaving the data with additional shuffles can be used to
+/// achieve the same.
+/// Below shows how 8 interleaved data are shuffled to store with stN
+/// instructions. Data need store in this order v0,v1,v2,v3,v4,v5,v6,v7
+///      v0      v4      v2      v6      v1      v5      v3      v7
+///      |       |       |       |       |       |       |       |
+///       \     /         \     /         \     /         \     /
+///     [zip v0,v4]      [zip v2,v6]    [zip v1,v5]      [zip v3,v7]==> stN = 4
+///          |               |              |                 |
+///           \             /                \               /
+///            \           /                  \             /
+///             \         /                    \           /
+///         [zip [v0,v2,v4,v6]]            [zip [v1,v3,v5,v7]]     ==> stN = 2
+///
+/// In stN = 4 level upper half of interleaved data V0,V1,V2,V3 is store
+/// withone st4 instruction. Lower half V4,V5,V6,V7 store with another st4.
+///
+/// In stN = 2 level first upper half of interleaved data V0,V1 is store
+/// with one st2 instruction. Second set V2,V3 with store with another st2.
+/// Total of 4 st2 are  required.
----------------
Rajveer100 wrote:

Nit.

```suggestion
/// If the interleaved vector elements are greater than supported MaxFactor,
/// interleaving the data with additional shuffles can be used to
/// achieve the same.
///
/// Consider the following data with 8 interleaves which are shuffled to store 
/// stN instructions. Data needs to be stored in this order:
///     [v0, v1, v2, v3, v4, v5, v6, v7]
///
///      v0      v4      v2      v6      v1      v5      v3      v7
///      |       |       |       |       |       |       |       |
///       \     /         \     /         \     /         \     /
///     [zip v0,v4]      [zip v2,v6]    [zip v1,v5]      [zip v3,v7] ==> stN = 4
///          |               |              |                 |
///           \             /                \               /
///            \           /                  \             /
///             \         /                    \           /
///         [zip [v0,v2,v4,v6]]            [zip [v1,v3,v5,v7]]     ==> stN = 2
///
/// For stN = 4, upper half of interleaved data V0, V1, V2, V3 is stored
/// with one st4 instruction. Lower half, i.e, V4, V5, V6, V7 is stored with 
/// another st4.
///
/// For stN = 2, upper half of interleaved data V0, V1 is stored
/// with one st2 instruction. Second set V2, V3 is stored with another st2.
/// Total of 4 st2's are required here.
```

https://github.com/llvm/llvm-project/pull/164000