[llvm] [VPlan] Extract reverse operation for reverse accesses (PR #146525)

[Florian Hahn via llvm-commits]

================
@@ -15,27 +15,27 @@ define void @lshift_significand(i32 %n, ptr nocapture writeonly %dst) {
 ; CHECK-NEXT:    [[TMP0:%.*]] = sub i64 3, [[SPEC_SELECT]]
 ; CHECK-NEXT:    br label %[[VECTOR_PH:.*]]
 ; CHECK:       [[VECTOR_PH]]:
+; CHECK-NEXT:    [[REVERSE:%.*]] = call <vscale x 2 x i64> @llvm.vector.reverse.nxv2i64(<vscale x 2 x i64> zeroinitializer)
----------------
fhahn wrote:

Would be good to add a fold `reverse(live-in/single-scalar) -> live-in/single-scalar`, as follow-up

https://github.com/llvm/llvm-project/pull/146525