[Strings] Work around ref.cast not working on string views, and add fuzzing (#6549)

As suggested in #6434 (comment) , lower ref.cast of string views
to ref.as_non_null in binary writing. It is a simple hack that avoids the
problem of V8 not allowing them to be cast.

Add fuzzing support for the last three core string operations, after which
that problem becomes very frequent.

Also add yet another makeTrappingRefUse that was missing in that
fuzzer code.

1 files changed, 66 insertions, 0 deletions

diff --git a/test/lit/passes/roundtrip.wast b/test/lit/passes/roundtrip.wast
index 59e303eaf..8fb69cb7d 100644
--- a/test/lit/passes/roundtrip.wast
+++ b/test/lit/passes/roundtrip.wast
@@ -42,4 +42,70 @@
    )
   )
  )
+
+ ;; CHECK:      (func $string_view_casts (type $2) (param $x stringview_wtf8) (param $y stringview_wtf16) (param $z stringview_iter)
+ ;; CHECK-NEXT:  (drop
+ ;; CHECK-NEXT:   (ref.as_non_null
+ ;; CHECK-NEXT:    (local.get $x)
+ ;; CHECK-NEXT:   )
+ ;; CHECK-NEXT:  )
+ ;; CHECK-NEXT:  (drop
+ ;; CHECK-NEXT:   (ref.as_non_null
+ ;; CHECK-NEXT:    (local.get $y)
+ ;; CHECK-NEXT:   )
+ ;; CHECK-NEXT:  )
+ ;; CHECK-NEXT:  (drop
+ ;; CHECK-NEXT:   (ref.as_non_null
+ ;; CHECK-NEXT:    (local.get $z)
+ ;; CHECK-NEXT:   )
+ ;; CHECK-NEXT:  )
+ ;; CHECK-NEXT:  (drop
+ ;; CHECK-NEXT:   (local.get $x)
+ ;; CHECK-NEXT:  )
+ ;; CHECK-NEXT:  (drop
+ ;; CHECK-NEXT:   (local.get $y)
+ ;; CHECK-NEXT:  )
+ ;; CHECK-NEXT:  (drop
+ ;; CHECK-NEXT:   (local.get $z)
+ ;; CHECK-NEXT:  )
+ ;; CHECK-NEXT: )
+ (func $string_view_casts
+  ;; ref.cast of string views is not allowed in binaries: replace with
+  ;; ref.as_non_null, or remove if it is a no-op.
+  (param $x (ref null stringview_wtf8))
+  (param $y (ref null stringview_wtf16))
+  (param $z (ref null stringview_iter))
+  ;; Here we still need a cast to non-null.
+  (drop
+   (ref.cast (ref stringview_wtf8)
+    (local.get $x)
+   )
+  )
+  (drop
+   (ref.cast (ref stringview_wtf16)
+    (local.get $y)
+   )
+  )
+  (drop
+   (ref.cast (ref stringview_iter)
+    (local.get $z)
+   )
+  )
+  ;; Here we do not need the cast.
+  (drop
+   (ref.cast (ref null stringview_wtf8)
+    (local.get $x)
+   )
+  )
+  (drop
+   (ref.cast (ref null stringview_wtf16)
+    (local.get $y)
+   )
+  )
+  (drop
+   (ref.cast (ref null stringview_iter)
+    (local.get $z)
+   )
+  )
+ )
 )