[llvm] [RISCV] Use a ta vslideup if inserting over end of InterSubVT (PR #83230)

[Luke Lau via llvm-commits]

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@@ -474,7 +474,7 @@ define <vscale x 6 x half> @extract_nxv6f16_nxv12f16_6(<vscale x 12 x half> %in)
 ; CHECK-NEXT:    vsetvli a1, zero, e16, m1, ta, ma
 ; CHECK-NEXT:    vslidedown.vx v12, v9, a0
 ; CHECK-NEXT:    add a1, a0, a0
-; CHECK-NEXT:    vsetvli zero, a1, e16, m1, tu, ma
+; CHECK-NEXT:    vsetvli zero, a1, e16, m1, ta, ma
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lukel97 wrote:

It's worth noting that a1 is VLMAX here through a series of computations. We should probably be detecting this in RISCVInsertVSETVLI and canonicalising it to `VLMaxSentinel`

https://github.com/llvm/llvm-project/pull/83230