Fix mem2reg test

examples/mem2reg/mem2reg.input.ir

@@ -8,6 +8,16 @@ block b0:
   ret unit:unit
 }
 
+fun unit @sinkptr {
+init:
+  bid: b0
+  allocations:
+
+block b0:
+  %b0:p0:*i8
+  ret unit:unit
+}
+
 fun i32 @single_block {
 init:
   bid: b0
@@ -100,8 +110,12 @@ init:
     %l0:i32:x
     %l1:i16:y
     %l2:i64:z
+    %l3:i8:w
 
 block b666:
+  %b666:i0:unit = store %l3:*i8 42:i8
+  %b666:i1:unit = call @sinkptr(%l3:*i8)
+  %b666:i2:i8 = load %l3:*i8
   j b0()
 
 block b0: