Only add exact casts when allowed in GUFA (#7518)

When custom descriptors are disabled, make sure the types of added casts
are inexact because exact casts would be invalid.

Author: tlively

scripts/test/fuzzing.py

@@ -122,6 +122,7 @@
     'coalesce-locals-exact.wast',
     'remove-unused-brs-exact.wast',
     'signature-refining-exact.wast',
+    'gufa-cast-all-exact.wast',
     # TODO: fuzzer support for custom descriptors
     'custom-descriptors.wast',
 ]

src/passes/GUFA.cpp

@@ -374,6 +374,11 @@ struct GUFAOptimizer
         }
 
         auto oracleType = parent.getContents(curr).getType();
+        // Exact casts are only allowed when custom descriptors is enabled.
+        if (oracleType.isExact() &&
+            !getModule()->features.hasCustomDescriptors()) {
+          oracleType = oracleType.with(Inexact);
+        }
         if (oracleType.isRef() && oracleType != curr->type &&
             Type::isSubType(oracleType, curr->type)) {
           replaceCurrent(Builder(*getModule()).makeRefCast(curr, oracleType));

test/lit/passes/gufa-cast-all-exact.wast

@@ -0,0 +1,54 @@
+;; NOTE: Assertions have been generated by update_lit_checks.py and should not be edited.
+
+;; Check that exact casts are only added when custom descriptors are enabled.
+
+;; RUN: wasm-opt %s -all                              --gufa-cast-all -S -o -  | filecheck %s
+;; RUN: wasm-opt %s -all --disable-custom-descriptors --gufa-cast-all -S -o -  | filecheck %s --check-prefix=NO_CD
+
+(module
+  ;; CHECK:      (type $foo (struct))
+  ;; NO_CD:      (type $foo (struct))
+  (type $foo (struct))
+
+  ;; CHECK:      (import "" "" (global $g (ref (exact $foo))))
+  ;; NO_CD:      (import "" "" (global $g (ref (exact $foo))))
+  (import "" "" (global $g (ref (exact $foo))))
+
+  ;; CHECK:      (func $callee (type $1) (result (ref $foo))
+  ;; CHECK-NEXT:  (global.get $g)
+  ;; CHECK-NEXT: )
+  ;; NO_CD:      (func $callee (type $1) (result (ref $foo))
+  ;; NO_CD-NEXT:  (global.get $g)
+  ;; NO_CD-NEXT: )
+  (func $callee (result (ref $foo))
+    (global.get $g)
+  )
+
+  ;; CHECK:      (func $caller (type $2)
+  ;; CHECK-NEXT:  (drop
+  ;; CHECK-NEXT:   (block (result (ref (exact $foo)))
+  ;; CHECK-NEXT:    (drop
+  ;; CHECK-NEXT:     (ref.cast (ref (exact $foo))
+  ;; CHECK-NEXT:      (call $callee)
+  ;; CHECK-NEXT:     )
+  ;; CHECK-NEXT:    )
+  ;; CHECK-NEXT:    (global.get $g)
+  ;; CHECK-NEXT:   )
+  ;; CHECK-NEXT:  )
+  ;; CHECK-NEXT: )
+  ;; NO_CD:      (func $caller (type $2)
+  ;; NO_CD-NEXT:  (drop
+  ;; NO_CD-NEXT:   (block (result (ref (exact $foo)))
+  ;; NO_CD-NEXT:    (drop
+  ;; NO_CD-NEXT:     (call $callee)
+  ;; NO_CD-NEXT:    )
+  ;; NO_CD-NEXT:    (global.get $g)
+  ;; NO_CD-NEXT:   )
+  ;; NO_CD-NEXT:  )
+  ;; NO_CD-NEXT: )
+  (func $caller
+    (drop
+      (call $callee)
+    )
+  )
+)