Handle exact references when fixing non-defaultable locals (#7357)

Some passes leave non-defaultable locals in an invalid state where not
all the gets of the local are structurally dominated by sets. To fix
this, the pass runner automatically calls
`TypeUpdating::handleNonDefaultableLocals` to find the problematic
locals and make them nullable. This function did not previously preserve
exactness in the updated local types. Fix it and add a test.

Author: tlively

scripts/test/fuzzing.py

@@ -106,6 +106,7 @@
     'optimize-instructions-exact.wast',
     'local-subtyping-exact.wast',
     'remove-unused-types-exact.wast',
+    'coalesce-locals-exact.wast',
 ]
 
 

src/ir/type-updating.cpp

@@ -467,7 +467,7 @@ void handleNonDefaultableLocals(Function* func, Module& wasm) {
 Type getValidLocalType(Type type, FeatureSet features) {
   assert(type.isConcrete());
   if (type.isNonNullable()) {
-    return Type(type.getHeapType(), Nullable);
+    return Type(type.getHeapType(), Nullable, type.getExactness());
   }
   if (type.isTuple()) {
     std::vector<Type> elems(type.size());

test/lit/passes/coalesce-locals-exact.wast

@@ -0,0 +1,47 @@
+;; NOTE: Assertions have been generated by update_lit_checks.py and should not be edited.
+
+;; Check that TypeUpdating::handleNonDefaultableLocals handles locals with exact
+;; reference types correctly, and in particular that it preserves the exactness
+;; of the types.
+
+;; RUN: wasm-opt %s -all --coalesce-locals -S -o - | filecheck %s
+
+(module
+ ;; CHECK:      (func $test (type $0) (param $0 (exact i31ref)) (result (ref exact i31))
+ ;; CHECK-NEXT:  (local $1 (exact i31ref))
+ ;; CHECK-NEXT:  (drop
+ ;; CHECK-NEXT:   (ref.as_non_null
+ ;; CHECK-NEXT:    (local.get $0)
+ ;; CHECK-NEXT:   )
+ ;; CHECK-NEXT:  )
+ ;; CHECK-NEXT:  (block $l
+ ;; CHECK-NEXT:   (local.set $1
+ ;; CHECK-NEXT:    (ref.as_non_null
+ ;; CHECK-NEXT:     (local.get $0)
+ ;; CHECK-NEXT:    )
+ ;; CHECK-NEXT:   )
+ ;; CHECK-NEXT:  )
+ ;; CHECK-NEXT:  (ref.as_non_null
+ ;; CHECK-NEXT:   (local.get $1)
+ ;; CHECK-NEXT:  )
+ ;; CHECK-NEXT: )
+ (func $test (param (exact i31ref)) (result (ref exact i31))
+  (local $l (ref exact i31))
+  ;; This dead set will be optimized out.
+  (local.set $l
+   (ref.as_non_null
+    (local.get 0)
+   )
+  )
+  (block $l
+   ;; This remaining set does not structurally dominate the get.
+   (local.set $l
+    (ref.as_non_null
+     (local.get 0)
+    )
+   )
+  )
+  ;; This will have to be fixed up and the local made nullable.
+  (local.get $l)
+ )
+)