fix corner case in reduce_vars (#5919)

fixes #5917

Author: alexlamsl

lib/compress.js

@@ -601,10 +601,6 @@ Compressor.prototype.compress = function(node) {
             fn.enclosed.forEach(function(d) {
                 if (fn.variables.get(d.name) === d) return;
                 if (safe_to_read(tw, d)) return;
-                d.single_use = false;
-                var fixed = d.fixed;
-                if (typeof fixed == "function") fixed = fixed();
-                if (fixed instanceof AST_Lambda && fixed.safe_ids !== undefined) return;
                 d.fixed = false;
             });
         }

test/compress/pure_getters.js

@@ -1715,3 +1715,39 @@ issue_5856: {
     }
     expect_stdout: "PASS"
 }
+
+issue_5917: {
+    options = {
+        pure_getters: "strict",
+        reduce_vars: true,
+        side_effects: true,
+        toplevel: true,
+    }
+    input: {
+        var a;
+        console || (a = function() {})(f);
+        function f() {
+            a.p;
+        }
+        try {
+            f();
+            console.log("FAIL");
+        } catch (e) {
+            console.log("PASS");
+        }
+    }
+    expect: {
+        var a;
+        console || (a = function() {})(f);
+        function f() {
+            a.p;
+        }
+        try {
+            f();
+            console.log("FAIL");
+        } catch (e) {
+            console.log("PASS");
+        }
+    }
+    expect_stdout: "PASS"
+}