[RISCV] Add test for doLocalPostpass issue not checking if VL was modified. NFC

Author: lukel97

llvm/test/CodeGen/RISCV/rvv/vsetvli-insert.mir

@@ -76,6 +76,10 @@
     ret void
   }
 
+  define void @postpass_modify_vl() {
+    ret void
+  }
+
   declare <vscale x 1 x i64> @llvm.riscv.vadd.nxv1i64.nxv1i64.i64(<vscale x 1 x i64>, <vscale x 1 x i64>, <vscale x 1 x i64>, i64) #1
 
   declare <vscale x 1 x i64> @llvm.riscv.vle.nxv1i64.i64(<vscale x 1 x i64>, ptr nocapture, i64) #4
@@ -503,3 +507,24 @@ body:             |
     %5:vr = PseudoVMV_V_I_MF2 $noreg, 1, 2, 5, 0
     PseudoRET
 ...
+---
+name:            postpass_modify_vl
+tracksRegLiveness: true
+body:             |
+  bb.0:
+    liveins: $x1
+    ; CHECK-LABEL: name: postpass_modify_vl
+    ; CHECK: liveins: $x1
+    ; CHECK-NEXT: {{  $}}
+    ; CHECK-NEXT: $x0 = PseudoVSETIVLI 3, 216 /* e64, m1, ta, ma */, implicit-def $vl, implicit-def $vtype
+    ; CHECK-NEXT: [[COPY:%[0-9]+]]:gpr = COPY $vtype
+    ; CHECK-NEXT: $vl = COPY $x1
+    ; CHECK-NEXT: [[PseudoVADD_VV_M1_:%[0-9]+]]:vr = PseudoVADD_VV_M1 $noreg, $noreg, $noreg, 3, 6 /* e64 */, 0 /* tu, mu */, implicit $vl, implicit $vtype
+    ; CHECK-NEXT: PseudoRET
+    dead $x0 = PseudoVSETIVLI 3, 216, implicit-def $vl, implicit-def $vtype
+    %1:gpr = COPY $vtype
+    $vl = COPY $x1
+    dead $x0 = PseudoVSETIVLI 3, 216, implicit-def $vl, implicit-def $vtype
+    %4:vr = PseudoVADD_VV_M1 $noreg, $noreg, $noreg, 3, 6, 0
+    PseudoRET
+...