Fix RefNull issues (#3123)

* ExpressionAnalyzer: Fix `ref.null ht` equality check to include `ht`.
* Precompute: Fix `ref.null ht` expression reuse to also update `ht`.
* Fuzzing: Fix `ref.null func` becoming canonicalized to `ref.func $funcref`
  when evaluating execution results, by adding a check for `isNull`.
* Fuzzing: Print actual and expected execution results when aborting.
* Tests: Update `if-arms-subtype` test in `optimize-instructions` to check
  that identical `if` arms become folded while not identical arms are kept.

2 files changed, 20 insertions, 4 deletions

diff --git a/test/passes/optimize-instructions_all-features.txt b/test/passes/optimize-instructions_all-features.txt
index f223cb838..31c1afbfc 100644
--- a/test/passes/optimize-instructions_all-features.txt
+++ b/test/passes/optimize-instructions_all-features.txt
@@ -10,11 +10,11 @@
  (type $i64_=>_i64 (func (param i64) (result i64)))
  (type $i32_i64_f32_=>_none (func (param i32 i64 f32)))
  (type $i32_i64_f32_f64_=>_none (func (param i32 i64 f32 f64)))
+ (type $none_=>_anyref (func (result anyref)))
  (type $i32_i32_i32_=>_none (func (param i32 i32 i32)))
  (type $i32_i32_f64_f64_=>_none (func (param i32 i32 f64 f64)))
  (type $i32_i64_f64_i32_=>_none (func (param i32 i64 f64 i32)))
  (type $none_=>_f64 (func (result f64)))
- (type $none_=>_anyref (func (result anyref)))
  (memory $0 0)
  (export "load-off-2" (func $load-off-2))
  (func $f (param $i1 i32) (param $i2 i64)
@@ -3712,9 +3712,16 @@
    (unreachable)
   )
  )
- (func $if-arms-subtype (result anyref)
+ (func $if-arms-subtype-fold (result anyref)
   (ref.null extern)
  )
+ (func $if-arms-subtype-nofold (result anyref)
+  (if (result anyref)
+   (i32.const 0)
+   (ref.null extern)
+   (ref.null func)
+  )
+ )
  (func $optimize-boolean-context (param $x i32) (param $y i32)
   (if
    (local.get $x)
diff --git a/test/passes/optimize-instructions_all-features.wast b/test/passes/optimize-instructions_all-features.wast
index 6e106ad1b..c2fa16e35 100644
--- a/test/passes/optimize-instructions_all-features.wast
+++ b/test/passes/optimize-instructions_all-features.wast
@@ -4207,8 +4207,17 @@
       (unreachable)
     )
   )
-  ;; Tests when if arms are subtype of if's type
-  (func $if-arms-subtype (result anyref)
+  ;; These functions test if an `if` with subtyped arms is correctly folded
+  ;; 1. if its `ifTrue` and `ifFalse` arms are identical (can fold)
+  (func $if-arms-subtype-fold (result anyref)
+    (if (result anyref)
+      (i32.const 0)
+      (ref.null extern)
+      (ref.null extern)
+    )
+  )
+  ;; 2. if its `ifTrue` and `ifFalse` arms are not identical (cannot fold)
+  (func $if-arms-subtype-nofold (result anyref)
     (if (result anyref)
       (i32.const 0)
       (ref.null extern)