[Multibyte] Handle ArrayStore in Precompute (#8511)

All GC writes must be handled there, to avoid it executing them and
thinking they have no more effects.

Author: kripken

src/passes/Precompute.cpp

@@ -215,6 +215,7 @@ class PrecomputingExpressionRunner
   }
   // ArrayLen is not disallowed here as it is an immutable property.
   Flow visitArrayCopy(ArrayCopy* curr) { return Flow(NONCONSTANT_FLOW); }
+  Flow visitArrayStore(ArrayStore* curr) { return Flow(NONCONSTANT_FLOW); }
 
   // Generates heap info for a heap-allocating expression.
   Flow getGCAllocation(Expression* curr, std::function<Flow()> visitFunc) {

test/lit/passes/precompute-gc-multibyte.wast

@@ -0,0 +1,24 @@
+;; NOTE: Assertions have been generated by update_lit_checks.py and should not be edited.
+
+;; RUN: foreach %s %t wasm-opt --precompute-propagate -all -S -o - | filecheck %s
+
+(module
+  ;; CHECK:      (type $array (array (mut i8)))
+  (type $array (array (mut i8)))
+
+  ;; CHECK:      (func $array.store (type $1) (param $x (ref $array))
+  ;; CHECK-NEXT:  (i64.store32 (type $array)
+  ;; CHECK-NEXT:   (local.get $x)
+  ;; CHECK-NEXT:   (i32.const 0)
+  ;; CHECK-NEXT:   (i64.const 1)
+  ;; CHECK-NEXT:  )
+  ;; CHECK-NEXT: )
+  (func $array.store (param $x (ref $array))
+    ;; ArrayStore operations cannot be removed.
+    (i64.store32 (type $array)
+      (local.get $x)
+      (i32.const 0)
+      (i64.const 1)
+    )
+  )
+)