[Custom Descriptors] Add effects for struct.new (#7690)

struct.new can now trap if provided a null descriptor. Update its
effects accordingly and add a test that would incorrectly remove a
trapping struct.new without this fix.

Author: tlively

scripts/test/fuzzing.py

@@ -125,6 +125,7 @@
     'minimize-rec-groups-desc.wast',
     'precompute-desc.wast',
     'gc-desc.wast',
+    'simplify-locals-desc.wast',
     # TODO: fix split_wast() on tricky escaping situations like a string ending
     #       in \\" (the " is not escaped - there is an escaped \ before it)
     'string-lifting-section.wast',

src/ir/effects.h

@@ -858,7 +858,16 @@ class EffectAnalyzer {
       parent.implicitTrap = true;
     }
     void visitBrOn(BrOn* curr) { parent.breakTargets.insert(curr->name); }
-    void visitStructNew(StructNew* curr) {}
+    void visitStructNew(StructNew* curr) {
+      if (curr->desc) {
+        // Traps when the descriptor is null.
+        if (curr->desc->type.isNull()) {
+          parent.trap = true;
+        } else if (curr->desc->type.isNullable()) {
+          parent.implicitTrap = true;
+        }
+      }
+    }
     void visitStructGet(StructGet* curr) {
       if (curr->ref->type == Type::unreachable) {
         return;

test/lit/passes/simplify-locals-desc.wast

@@ -0,0 +1,31 @@
+;; NOTE: Assertions have been generated by update_lit_checks.py and should not be edited.
+
+;; RUN: wasm-opt %s --simplify-locals -all -S -o - | filecheck %s
+
+(module
+ (rec
+  ;; CHECK:      (rec
+  ;; CHECK-NEXT:  (type $struct (descriptor $desc (struct)))
+  (type $struct (descriptor $desc (struct)))
+  ;; CHECK:       (type $desc (sub (describes $struct (struct))))
+  (type $desc (sub (describes $struct (struct))))
+ )
+
+ ;; CHECK:      (func $test (type $2)
+ ;; CHECK-NEXT:  (local $l (ref null $struct))
+ ;; CHECK-NEXT:  (drop
+ ;; CHECK-NEXT:   (struct.new_default $struct
+ ;; CHECK-NEXT:    (ref.null none)
+ ;; CHECK-NEXT:   )
+ ;; CHECK-NEXT:  )
+ ;; CHECK-NEXT: )
+ (func $test (export "test")
+  (local $l (ref null $struct))
+  (local.set $l
+   ;; We should preserve this trap.
+   (struct.new_default $struct
+    (ref.null none)
+   )
+  )
+ )
+)