fixup! add comment to test

Author: michaelmaitland

llvm/test/CodeGen/RISCV/rvv/vlopt-same-vl.ll

@@ -3,6 +3,13 @@
 
 ; REQUIRES: asserts
 
+; GitHub Issue #123862 provided a case where the riscv-vl-optimizer pass was
+; very slow. It was found that that case benefited greatly from aborting due
+; to CommonVL == VLOp. Adding the case provided in the issue would show up
+; as a long running test instead of a test failure. We would likley have a hard
+; time figuring if that case had a regression. So instead, we check this output
+; which was responsible for speeding it up. 
+
 define <vscale x 4 x i32> @same_vl_imm(<vscale x 4 x i32> %passthru, <vscale x 4 x i32> %a, <vscale x 4 x i32> %b) {
   ; CHECK: User VL is: 4
   ; CHECK-NEXT: Abort due to CommonVL == VLOp, no point in reducing.