fix corner case in evaluate (#3559)

fixes #3558

Author: alexlamsl

lib/compress.js

@@ -2862,10 +2862,10 @@ merge(Compressor.prototype, {
               case "+": return +v;
               case "++":
               case "--":
-                if (e instanceof AST_SymbolRef) {
-                    var refs = e.definition().references;
-                    if (refs[refs.length - 1] === e) return v;
-                }
+                if (!(e instanceof AST_SymbolRef)) return this;
+                var refs = e.definition().references;
+                if (refs[refs.length - 1] !== e) return this;
+                return HOP(e, "_eval") ? +(this.operator[0] + 1) + +v : v;
             }
             return this;
         });

test/compress/evaluate.js

@@ -1838,3 +1838,24 @@ recursive_function_2: {
     }
     expect_stdout: "120"
 }
+
+issue_3558: {
+    options = {
+        evaluate: true,
+        reduce_vars: true,
+        toplevel: true,
+    }
+    input: {
+        function f(a) {
+            return 1 + --a;
+        }
+        console.log(f(true), f(false));
+    }
+    expect: {
+        function f(a) {
+            return 1 + --a;
+        }
+        console.log(1, 0);
+    }
+    expect_stdout: "1 0"
+}