[llvm] [RISCV] Enabled masked interleaved access (PR #149981)

[Mel Chen via llvm-commits]

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@@ -1358,7 +1358,9 @@ class LoopVectorizationCostModel {
       return;
     // Override forced styles if needed.
     // FIXME: Investigate opportunity for fixed vector factor.
+    // FIXME: Support interleave accesses.
     bool EVLIsLegal = UserIC <= 1 && IsScalableVF &&
+                      !InterleaveInfo.hasGroups() &&
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Mel-Chen wrote:

Hmm, although I previously said the mask might be incorrect, it’s actually different from what you described.
```
; IF-EVL-NEXT:    [[BROADCAST_SPLATINSERT1:%.*]] = insertelement <vscale x 4 x i64> poison, i64 [[EVL_BASED_IV]], i64 0
; IF-EVL-NEXT:    [[BROADCAST_SPLAT2:%.*]] = shufflevector <vscale x 4 x i64> [[BROADCAST_SPLATINSERT1]], <vscale x 4 x i64> poison, <vscale x 4 x i32> zeroinitializer
; IF-EVL-NEXT:    [[TMP10:%.*]] = call <vscale x 4 x i64> @llvm.stepvector.nxv4i64()
; IF-EVL-NEXT:    [[TMP12:%.*]] = add <vscale x 4 x i64> zeroinitializer, [[TMP10]]
; IF-EVL-NEXT:    [[VEC_IV:%.*]] = add <vscale x 4 x i64> [[BROADCAST_SPLAT2]], [[TMP12]]
; IF-EVL-NEXT:    [[TMP13:%.*]] = icmp ule <vscale x 4 x i64> [[VEC_IV]], [[BROADCAST_SPLAT]]
```
In reality, the two masks should be: [T, T, T, T, T, T, T, T] and [T, T, T, T, F, F, F, F].

For the first iteration:
([0, 0, 0, 0] + [0, 1, 2, 3]) <= [4, 4, 4, 4], where 4 is TripCount - 1.

For the second iteration:
([3, 3, 3, 3] + [0, 1, 2, 3]) <= [4, 4, 4, 4].

Is that correct?

https://github.com/llvm/llvm-project/pull/149981