[Strings] Fix effects of string.compare and add fuzzing (#6547)

We added string.compare late in the spec process, and forgot to add effects for it.
Unlike string.eq, it can trap.

Also use makeTrappingRefUse in recent fuzzer string generation places that I
forgot, which should reduce the amount of traps in fuzzer output.

1 files changed, 8 insertions, 1 deletions

diff --git a/src/ir/effects.h b/src/ir/effects.h
index 3ecb54641..ef9aceb37 100644
--- a/src/ir/effects.h
+++ b/src/ir/effects.h
@@ -989,7 +989,14 @@ private:
       // traps when an input is null.
       parent.implicitTrap = true;
     }
-    void visitStringEq(StringEq* curr) {}
+    void visitStringEq(StringEq* curr) {
+      if (curr->op == StringEqCompare) {
+        // traps when either input is null.
+        if (curr->left->type.isNullable() || curr->right->type.isNullable()) {
+          parent.implicitTrap = true;
+        }
+      }
+    }
     void visitStringAs(StringAs* curr) {
       // traps when ref is null.
       parent.implicitTrap = true;