fix corner case in evaluate (#5559)

fixes #5558

lib/compress.js

@@ -5030,6 +5030,7 @@ Compressor.prototype.compress = function(node) {
                     if (def.undeclared) return this;
                     if (def.last_ref !== lhs) return this;
                     if (def.single_use == "m") return this;
+                    if (this.right.has_side_effects(compressor)) return this;
                 }
             }
             var op = this.operator;

test/compress/evaluate.js

@@ -3390,3 +3390,29 @@ issue_5380: {
     }
     expect_stdout: "PASS"
 }
+
+issue_5558: {
+    options = {
+        collapse_vars: true,
+        evaluate: true,
+        reduce_vars: true,
+        sequences: true,
+        toplevel: true,
+    }
+    input: {
+        var a = 99, b = 0;
+        a++;
+        b++;
+        b += a;
+        b *= a;
+        b += a;
+        console.log(a);
+    }
+    expect: {
+        var a = 99, b = 0;
+        b++,
+        b = (b += ++a) * a + a,
+        console.log(a);
+    }
+    expect_stdout: "100"
+}