test(optimizer): cover folded type-check side effects

tests/compiler/optimizations/is-type-fold-side-effects.phpt

@@ -20,6 +20,18 @@ function boolSource(): bool
     return true;
 }
 
+function assignmentSource(): int
+{
+    echo "assignment-called\n";
+    return 73;
+}
+
+function exceptionSource(): int
+{
+    echo "exception-called\n";
+    throw new RuntimeException('folded-exception');
+}
+
 function main(): void
 {
     if (is_int(intSource())) {
@@ -32,6 +44,20 @@ function main(): void
     // Plain variables still fold without extra evaluation.
     $n = 7;
     echo is_int($n) ? "var-int\n" : "var-not-int\n";
+
+    // The folded operand must run exactly once and preserve its result.
+    $assigned = 0;
+    echo is_int($assigned = assignmentSource()) ? "assigned-int\n" : "assigned-not-int\n";
+    echo "assigned-value=", $assigned, "\n";
+
+    // Folding the predicate must not suppress an exception from its operand.
+    try {
+        if (is_int(exceptionSource())) {
+            echo "exception-not-thrown\n";
+        }
+    } catch (RuntimeException $e) {
+        echo "caught=", $e->getMessage(), "\n";
+    }
 }
 ?>
 --EXPECT--
@@ -42,3 +68,8 @@ is-float
 bool-called
 is-bool
 var-int
+assignment-called
+assigned-int
+assigned-value=73
+exception-called
+caught=folded-exception