TypeRefining-GUFA: Fix bug with considering continuation fields empty (#8150)

We must skip such fields and not refine them, as we can't use casts to
fix up refinement issues. But we were just not writing anything to GUFA's
tracking of that location, which meant it looked unwritten - hence any
reads would be unreachable, and trap. To fix this, just write the
current type there.

Author: kripken

src/passes/TypeRefining.cpp

@@ -210,9 +210,9 @@ struct TypeRefining : public Pass {
             gufaType = gufaType.withInexactIfNoCustomDescs(module->features);
           }
           // Do not use the GUFA type if it is a continuation, as we cannot add
-          // casts to fix up issues later.
+          // casts to fix up issues later. Instead, use the original type.
           if (gufaType.isContinuation()) {
-            continue;
+            gufaType = fields[i].type;
           }
           infos[i] = LUBFinder(gufaType);
         }

test/lit/passes/type-refining-gufa.wast

@@ -476,3 +476,148 @@
   )
  )
 )
+
+;; $wrap-cont has a continuation field, a type which we must not modify. There
+;; are other optimization opportunities in the module ($wrap-array's field can
+;; become exact), so we end up optimizing here. While doing so, we must not
+;; change the continuation type (due to cast limitations), and we must not get
+;; confused and think there is no value in that field because of that
+;; restriction (if we did, the outer struct.get in $a would trap, as it would be
+;; reading from a place nothing was written to, so it would need to be
+;; unreachable).
+(module
+ ;; NRML:      (type $func (func))
+ ;; GUFA:      (type $func (func))
+ ;; O3O3:      (type $func (func))
+ (type $func (func))
+ (rec
+  ;; NRML:      (rec
+  ;; NRML-NEXT:  (type $cont (cont $func))
+  ;; GUFA:      (rec
+  ;; GUFA-NEXT:  (type $cont (cont $func))
+  ;; O3O3:      (rec
+  ;; O3O3-NEXT:  (type $cont (cont $func))
+  (type $cont (cont $func))
+  ;; NRML:       (type $wrap-cont (struct (field (ref $cont))))
+  ;; GUFA:       (type $wrap-cont (struct (field (ref $cont))))
+  ;; O3O3:       (type $wrap-cont (struct (field (ref $cont))))
+  (type $wrap-cont (struct (field (ref $cont))))
+ )
+ ;; NRML:      (rec
+ ;; NRML-NEXT:  (type $array (array i32))
+ ;; GUFA:      (rec
+ ;; GUFA-NEXT:  (type $array (array i32))
+ (type $array (array i32))
+ ;; NRML:       (type $wrap-array (sub (struct (field (ref (exact $array))))))
+ ;; GUFA:       (type $wrap-array (sub (struct (field (ref (exact $array))))))
+ (type $wrap-array (sub (struct (field (ref $array)))))
+
+ ;; NRML:      (type $5 (func (result (ref $cont))))
+
+ ;; NRML:      (elem declare func $ref)
+
+ ;; NRML:      (export "a" (func $a))
+ ;; GUFA:      (type $5 (func (result (ref $cont))))
+
+ ;; GUFA:      (elem declare func $ref)
+
+ ;; GUFA:      (export "a" (func $a))
+ ;; O3O3:      (type $3 (func (result (ref $cont))))
+
+ ;; O3O3:      (elem declare func $ref)
+
+ ;; O3O3:      (export "a" (func $a))
+ (export "a" (func $a))
+ ;; NRML:      (export "b" (func $b))
+ ;; GUFA:      (export "b" (func $b))
+ ;; O3O3:      (export "b" (func $b))
+ (export "b" (func $b))
+
+ ;; NRML:      (func $a (type $func)
+ ;; NRML-NEXT:  (drop
+ ;; NRML-NEXT:   (struct.get $wrap-cont 0
+ ;; NRML-NEXT:    (struct.new $wrap-cont
+ ;; NRML-NEXT:     (cont.new $cont
+ ;; NRML-NEXT:      (ref.func $ref)
+ ;; NRML-NEXT:     )
+ ;; NRML-NEXT:    )
+ ;; NRML-NEXT:   )
+ ;; NRML-NEXT:  )
+ ;; NRML-NEXT: )
+ ;; GUFA:      (func $a (type $func)
+ ;; GUFA-NEXT:  (drop
+ ;; GUFA-NEXT:   (struct.get $wrap-cont 0
+ ;; GUFA-NEXT:    (struct.new $wrap-cont
+ ;; GUFA-NEXT:     (cont.new $cont
+ ;; GUFA-NEXT:      (ref.func $ref)
+ ;; GUFA-NEXT:     )
+ ;; GUFA-NEXT:    )
+ ;; GUFA-NEXT:   )
+ ;; GUFA-NEXT:  )
+ ;; GUFA-NEXT: )
+ ;; O3O3:      (func $a (type $func)
+ ;; O3O3-NEXT:  (drop
+ ;; O3O3-NEXT:   (cont.new $cont
+ ;; O3O3-NEXT:    (ref.func $ref)
+ ;; O3O3-NEXT:   )
+ ;; O3O3-NEXT:  )
+ ;; O3O3-NEXT: )
+ (func $a
+  ;; GUFA cannot improve things here (-O3 can remove the struct operations,
+  ;; though).
+  (drop
+   (struct.get $wrap-cont 0
+    (struct.new $wrap-cont
+     (cont.new $cont
+      (ref.func $ref)
+     )
+    )
+   )
+  )
+ )
+
+ ;; NRML:      (func $b (type $5) (result (ref $cont))
+ ;; NRML-NEXT:  (unreachable)
+ ;; NRML-NEXT: )
+ ;; GUFA:      (func $b (type $5) (result (ref $cont))
+ ;; GUFA-NEXT:  (unreachable)
+ ;; GUFA-NEXT: )
+ ;; O3O3:      (func $b (type $3) (result (ref $cont))
+ ;; O3O3-NEXT:  (unreachable)
+ ;; O3O3-NEXT: )
+ (func $b (result (ref $cont))
+  (unreachable)
+ )
+
+ ;; NRML:      (func $ref (type $func)
+ ;; NRML-NEXT:  (drop
+ ;; NRML-NEXT:   (struct.new $wrap-array
+ ;; NRML-NEXT:    (array.new_default $array
+ ;; NRML-NEXT:     (i32.const 0)
+ ;; NRML-NEXT:    )
+ ;; NRML-NEXT:   )
+ ;; NRML-NEXT:  )
+ ;; NRML-NEXT: )
+ ;; GUFA:      (func $ref (type $func)
+ ;; GUFA-NEXT:  (drop
+ ;; GUFA-NEXT:   (struct.new $wrap-array
+ ;; GUFA-NEXT:    (array.new_default $array
+ ;; GUFA-NEXT:     (i32.const 0)
+ ;; GUFA-NEXT:    )
+ ;; GUFA-NEXT:   )
+ ;; GUFA-NEXT:  )
+ ;; GUFA-NEXT: )
+ ;; O3O3:      (func $ref (type $func)
+ ;; O3O3-NEXT:  (nop)
+ ;; O3O3-NEXT: )
+ (func $ref (type $func)
+  (drop
+   (struct.new $wrap-array
+    (array.new_default $array
+     (i32.const 0)
+    )
+   )
+  )
+ )
+)
+