Convert the CFG traversal tests to file tests.

Add a "cfg_postorder:" printout to the "test domtree" file tests and use
that to check the computed CFG post-order instead of doing it manually
with Rust code.

cranelift/filetests/domtree/basic.cton

@@ -11,3 +11,8 @@ function %test(i32) {
     ebb3:
         return
 }
+; check: cfg_postorder:
+; sameln: ebb2
+; sameln: ebb3
+; sameln: ebb1
+; sameln: ebb0

cranelift/filetests/domtree/loops.cton

@@ -18,3 +18,67 @@ function %test(i32) {
         brz v0, ebb4
         return
 }
+; Fall-through-first, prune-at-source DFT:
+;
+; ebb0 {
+;     ebb0:brz v0, ebb1 {
+;         ebb0:jump ebb2 {
+;             ebb2 {
+;                 ebb2:brz v2, ebb2 -
+;                 ebb2:brz v3, ebb1 -
+;                 ebb2:brz v4, ebb4 {
+;                     ebb2: jump ebb5 {
+;                         ebb5 {}
+;                     }
+;                     ebb4 {}
+;                 }
+;             } ebb2
+;         }
+;         ebb1 {
+;             ebb1:jump ebb3 {
+;                 ebb3 {}
+;             }
+;         } ebb1
+;     }
+; } ebb0
+;
+; check: cfg_postorder:
+; sameln: ebb5
+; sameln: ebb3
+; sameln: ebb4
+; sameln: ebb2
+; sameln: ebb1
+; sameln: ebb0
+
+function %loop2(i32) native {
+    ebb0(v0: i32):
+        brz v0, ebb1    ; dominates: ebb1 ebb3 ebb4 ebb5
+        jump ebb2       ; dominates: ebb2
+    ebb1:
+        jump ebb3
+    ebb2:
+        brz v0, ebb4
+        jump ebb5
+    ebb3:
+        jump ebb4
+    ebb4:
+        brz v0, ebb3
+        brnz v0, ebb5
+        jump ebb6       ; dominates: ebb6
+    ebb5:
+        brz v0, ebb4
+        trap user0
+    ebb6:
+        jump ebb7       ; dominates: ebb7
+    ebb7:
+        return
+}
+; check: cfg_postorder:
+; sameln: ebb5
+; sameln: ebb7
+; sameln: ebb6
+; sameln: ebb3
+; sameln: ebb4
+; sameln: ebb2
+; sameln: ebb1
+; sameln: ebb0

cranelift/filetests/domtree/loops2.cton

@@ -29,3 +29,29 @@ function %test(i32) {
     ebb9:
         return
 }
+
+function %test(i32) native {
+    ebb0(v0: i32):
+        brz v0, ebb1    ; dominates: ebb1 ebb3 ebb4 ebb5
+        jump ebb2       ; dominates: ebb2
+    ebb1:
+        jump ebb3
+    ebb2:
+        brz v0, ebb4
+        jump ebb5
+    ebb3:
+        jump ebb4
+    ebb4:
+        brz v0, ebb3
+        jump ebb5
+    ebb5:
+        brz v0, ebb4
+        return
+}
+; check: cfg_postorder:
+; sameln: ebb5
+; sameln: ebb3
+; sameln: ebb4
+; sameln: ebb2
+; sameln: ebb1
+; sameln: ebb0