Update TypeMerging for exact types (#7521)

Do not merge types that differ in exactness.

Author: tlively

scripts/test/fuzzing.py

@@ -123,6 +123,7 @@
     'remove-unused-brs-exact.wast',
     'signature-refining-exact.wast',
     'gufa-cast-all-exact.wast',
+    'type-merging-exact.wast',
     # TODO: fuzzer support for custom descriptors
     'custom-descriptors.wast',
 ]

src/passes/TypeMerging.cpp

@@ -667,6 +667,9 @@ bool shapeEq(Type a, Type b) {
   if (a.getNullability() != b.getNullability()) {
     return false;
   }
+  if (a.getExactness() != b.getExactness()) {
+    return false;
+  }
   return true;
 }
 
@@ -688,6 +691,7 @@ size_t shapeHash(Type a) {
   }
   rehash(digest, 4);
   rehash(digest, (int)a.getNullability());
+  rehash(digest, (int)a.getExactness());
   return digest;
 }
 

test/lit/passes/type-merging-exact.wast

@@ -0,0 +1,21 @@
+;; NOTE: Assertions have been generated by update_lit_checks.py and should not be edited.
+
+;; Check that types that differ only in exactness are not merged.
+
+;; RUN: wasm-opt %s -all --closed-world --preserve-type-order \
+;; RUN:     --type-merging --remove-unused-types -S -o - | filecheck %s
+
+(module
+ ;; CHECK:      (rec
+ ;; CHECK-NEXT:  (type $foo (struct))
+ (type $foo (struct))
+ ;; CHECK:       (type $A (struct (field (ref (exact $foo)))))
+ (type $A (struct (field (ref (exact $foo)))))
+ ;; CHECK:       (type $B (struct (field (ref $foo))))
+ (type $B (struct (field (ref $foo))))
+
+ ;; CHECK:      (global $a (ref null $A) (ref.null none))
+ (global $a (ref null $A) (ref.null none))
+ ;; CHECK:      (global $b (ref null $B) (ref.null none))
+ (global $b (ref null $B) (ref.null none))
+)