Preserve exactness when updating types (#7512)

Fix a place where we failed to propagate exactness in type-updating.cpp.

Author: tlively

scripts/test/fuzzing.py

@@ -118,6 +118,7 @@
     'remove-unused-types-exact.wast',
     'coalesce-locals-exact.wast',
     'remove-unused-brs-exact.wast',
+    'signature-refining-exact.wast',
     # TODO: fuzzer support for custom descriptors
     'custom-descriptors.wast',
 ]

src/ir/type-updating.cpp

@@ -346,9 +346,8 @@ Type GlobalTypeRewriter::getTempType(Type type) {
   if (type.isRef()) {
     auto heapType = type.getHeapType();
     if (auto it = typeIndices.find(heapType); it != typeIndices.end()) {
-      // TODO: Handle exactness.
-      return typeBuilder.getTempRefType(typeBuilder[it->second],
-                                        type.getNullability());
+      return typeBuilder.getTempRefType(
+        typeBuilder[it->second], type.getNullability(), type.getExactness());
     }
     // This type is not one that is eligible for optimizing. That is fine; just
     // use it unmodified.

test/lit/passes/signature-refining-exact.wast

@@ -0,0 +1,31 @@
+;; NOTE: Assertions have been generated by update_lit_checks.py --all-items and should not be edited.
+;; RUN: wasm-opt %s --signature-refining -all -S -o - | filecheck %s
+
+;; Check that we can refine signatures to contain exact references correctly.
+
+(module
+ ;; CHECK:      (rec
+ ;; CHECK-NEXT:  (type $f (func))
+ (type $f (func))
+
+ ;; CHECK:       (type $1 (func (param (ref null (exact $f))) (result (ref null (exact $f)))))
+
+ ;; CHECK:      (func $foo (type $1) (param $0 (ref null (exact $f))) (result (ref null (exact $f)))
+ ;; CHECK-NEXT:  (local $1 (ref null (exact $f)))
+ ;; CHECK-NEXT:  (drop
+ ;; CHECK-NEXT:   (call $foo
+ ;; CHECK-NEXT:    (local.get $1)
+ ;; CHECK-NEXT:   )
+ ;; CHECK-NEXT:  )
+ ;; CHECK-NEXT:  (local.get $1)
+ ;; CHECK-NEXT: )
+ (func $foo (param funcref) (result funcref)
+  (local (ref null (exact $f)))
+  (drop
+   (call $foo
+    (local.get 1)
+   )
+  )
+  (local.get 1)
+ )
+)