[wasm-reduce] Do not crash on non-func element segments

Generalize the code for simplifying element segments to handle more than
just null and funcref elements.

src/tools/wasm-reduce.cpp

@@ -854,18 +854,14 @@ struct Reducer
       reduceByZeroing(
         segment.get(),
         first,
-        [&](Expression* entry) {
-          if (entry->is<RefNull>()) {
-            // we don't need to replace a ref.null
+        [&](Expression* elem) {
+          if (elem->is<RefNull>()) {
+            // We don't need to replace a ref.null.
             return true;
-          } else if (first->is<RefNull>()) {
-            return false;
-          } else {
-            // Both are ref.func
-            auto* f = first->cast<RefFunc>();
-            auto* e = entry->cast<RefFunc>();
-            return f->func == e->func;
           }
+          // Replace the element if it is different from our first "zero"
+          // element.
+          return !ExpressionAnalyzer::equal(first, elem);
         },
         1,
         shrank);

test/reduce/memory_table.wast

@@ -2,12 +2,15 @@
  (type $i (func (result i32)))
  (memory $0 256 256)
  (table 481 481 funcref)
+ (table 354 354 i31ref)
  (elem (i32.const 0) $f0 $f0 $f1 $f2 $f0 $f3 $f0)
+ (elem (table 1) (i32.const 0) i31ref (item (ref.i31 (i32.const 0))) (item (ref.i31 (i32.const 1))))
  (data (i32.const 0) "p\0bflkj")
  (data (i32.const 10960) "1234hello")
  (export "f1" (func $f1))
  (export "f2" (func $f2))
  (export "f4" (func $f4))
+ (export "f5" (func $f5))
  (func $f0 (result i32)
   (i32.const 1234)
  )
@@ -27,5 +30,10 @@
    (call_indirect (type $i) (i32.const 0))
   )
  )
+ (func $f5 (result i32)
+  (i32.add
+   (i31.get_s (table.get 1 (i32.const 0)))
+   (i31.get_u (table.get 1 (i32.const 1)))
+  )
+ )
 )
-

test/reduce/memory_table.wast.txt

@@ -5,6 +5,7 @@
  (export "f1" (func $0))
  (export "f2" (func $1))
  (export "f4" (func $2))
+ (export "f5" (func $3))
  (func $0
  )
  (func $1 (result i32)
@@ -22,5 +23,8 @@
    (i32.const 1234)
   )
  )
+ (func $3 (result i32)
+  (i32.const 1)
+ )
 )