[Wasm GC] Fix struct.set / ref.as_non_null ordering issue (#5474)

If traps can happen, then we can't always remove a trap on null
on the ref input to struct.set, since it has two children,

(struct.set
  (ref.as_non_null X)
  (call $foo))

Removing the ref.as would not prevent a trap, as the struct.set
will trap, but it does move the trap to after the call which is bad.

1 files changed, 47 insertions, 0 deletions

diff --git a/test/lit/passes/optimize-instructions-gc-tnh.wast b/test/lit/passes/optimize-instructions-gc-tnh.wast
index 2307362ff..87795f31d 100644
--- a/test/lit/passes/optimize-instructions-gc-tnh.wast
+++ b/test/lit/passes/optimize-instructions-gc-tnh.wast
@@ -11,6 +11,10 @@
   ;; NO_TNH:      (type $void (func))
   (type $void (func))
 
+  ;; TNH:      (import "a" "b" (func $import (result i32)))
+  ;; NO_TNH:      (import "a" "b" (func $import (result i32)))
+  (import "a" "b" (func $import (result i32)))
+
   ;; TNH:      (func $ref.eq (type $eqref_eqref_=>_i32) (param $a eqref) (param $b eqref) (result i32)
   ;; TNH-NEXT:  (ref.eq
   ;; TNH-NEXT:   (local.get $a)
@@ -603,6 +607,49 @@
     )
   )
 
+  ;; TNH:      (func $null.cast-other.effects (type $ref?|$struct|_=>_none) (param $x (ref null $struct))
+  ;; TNH-NEXT:  (struct.set $struct 0
+  ;; TNH-NEXT:   (local.get $x)
+  ;; TNH-NEXT:   (call $import)
+  ;; TNH-NEXT:  )
+  ;; TNH-NEXT:  (struct.set $struct 0
+  ;; TNH-NEXT:   (local.get $x)
+  ;; TNH-NEXT:   (i32.const 10)
+  ;; TNH-NEXT:  )
+  ;; TNH-NEXT: )
+  ;; NO_TNH:      (func $null.cast-other.effects (type $ref?|$struct|_=>_none) (param $x (ref null $struct))
+  ;; NO_TNH-NEXT:  (struct.set $struct 0
+  ;; NO_TNH-NEXT:   (ref.as_non_null
+  ;; NO_TNH-NEXT:    (local.get $x)
+  ;; NO_TNH-NEXT:   )
+  ;; NO_TNH-NEXT:   (call $import)
+  ;; NO_TNH-NEXT:  )
+  ;; NO_TNH-NEXT:  (struct.set $struct 0
+  ;; NO_TNH-NEXT:   (local.get $x)
+  ;; NO_TNH-NEXT:   (i32.const 10)
+  ;; NO_TNH-NEXT:  )
+  ;; NO_TNH-NEXT: )
+  (func $null.cast-other.effects (param $x (ref null $struct))
+    (struct.set $struct 0
+      ;; We cannot remove this ref.as_non_null, even though the struct.set will
+      ;; trap if the ref is null, because that would move the trap from before
+      ;; the call to the import to be after it. But in TNH we can assume it does
+      ;; not trap, and remove it.
+      (ref.as_non_null
+        (local.get $x)
+      )
+      (call $import)
+    )
+    (struct.set $struct 0
+      ;; This one can be removed even without TNH, as there are no effects after
+      ;; it.
+      (ref.as_non_null
+        (local.get $x)
+      )
+      (i32.const 10)
+    )
+  )
+
   ;; Helper functions.
 
   ;; TNH:      (func $get-i32 (type $none_=>_i32) (result i32)