fix corner case in reduce_vars (#5873)

fixes #5872

Author: alexlamsl

lib/compress.js

@@ -654,12 +654,20 @@ Compressor.prototype.compress = function(node) {
         }
 
         function access(tw, def) {
-            tw.defined_ids[def.id] = [ tw.defined_ids.seq ];
+            tw.defined_ids[def.id] = tw.defined_ids.seq;
         }
 
         function assign(tw, def) {
+            tw.assigned_ids[def.id] = tw.defined_ids.seq;
+            tw.defined_ids[def.id] = false;
+        }
+
+        function safe_to_access(tw, def) {
+            var seq = tw.defined_ids.seq;
             var defined = tw.defined_ids[def.id];
-            if (defined) defined[0] = false;
+            if (defined !== seq) return false;
+            var assigned = tw.assigned_ids[def.id];
+            return !assigned || assigned === seq;
         }
 
         function mark(tw, def) {
@@ -1424,8 +1432,7 @@ Compressor.prototype.compress = function(node) {
             var d = ref.definition();
             var fixed = d.fixed || d.last_ref && d.last_ref.fixed;
             push_ref(d, ref);
-            var defined = tw.defined_ids[d.id];
-            if (defined && defined[0] === tw.defined_ids.seq) ref.defined = true;
+            if (safe_to_access(tw, d)) ref.defined = true;
             if (d.references.length == 1 && !d.fixed && d.orig[0] instanceof AST_SymbolDefun) {
                 tw.loop_ids[d.id] = tw.in_loop;
             }
@@ -1656,6 +1663,7 @@ Compressor.prototype.compress = function(node) {
             return node.reduce_vars(tw, descend, compressor);
         } : reset_flags);
         // Side-effect tracking on sequential property access
+        tw.assigned_ids = Object.create(null);
         tw.defined_ids = Object.create(null);
         tw.defined_ids.seq = {};
         // Flow control for visiting lambda definitions

test/compress/reduce_vars.js

@@ -8346,3 +8346,119 @@ issue_1666_undefined_strict: {
     }
     expect_stdout: true
 }
+
+issue_5872_1: {
+    options = {
+        pure_getters: "strict",
+        reduce_vars: true,
+        side_effects: true,
+    }
+    input: {
+        var a = 42;
+        try {
+            while (!function f() {
+                a.p;
+                a = null;
+            }(a.q)) {
+                a.r;
+                console.log("FAIL");
+            }
+        } catch (e) {
+            console.log("PASS");
+        }
+    }
+    expect: {
+        var a = 42;
+        try {
+            while (!function f() {
+                a.p;
+                a = null;
+            }(a.q)) {
+                a.r;
+                console.log("FAIL");
+            }
+        } catch (e) {
+            console.log("PASS");
+        }
+    }
+    expect_stdout: "PASS"
+}
+
+issue_5872_2: {
+    options = {
+        pure_getters: "strict",
+        reduce_vars: true,
+        side_effects: true,
+        toplevel: true,
+    }
+    input: {
+        function f() {
+            a.p;
+            a = null;
+        }
+
+        var a = 42;
+        try {
+            while (!f(a.q)) {
+                a.r;
+                console.log("FAIL");
+            }
+        } catch (e) {
+            console.log("PASS");
+        }
+    }
+    expect: {
+        function f() {
+            a.p;
+            a = null;
+        }
+
+        var a = 42;
+        try {
+            while (!f(a.q)) {
+                a.r;
+                console.log("FAIL");
+            }
+        } catch (e) {
+            console.log("PASS");
+        }
+    }
+    expect_stdout: "PASS"
+}
+
+issue_5872_3: {
+    options = {
+        pure_getters: "strict",
+        reduce_vars: true,
+        side_effects: true,
+    }
+    input: {
+        var a = 42;
+        try {
+            while (new function() {
+                a.p;
+                a = null;
+            }(a.q)) {
+                a.r;
+                console.log("FAIL");
+            }
+        } catch (e) {
+            console.log("PASS");
+        }
+    }
+    expect: {
+        var a = 42;
+        try {
+            while (new function() {
+                a.p;
+                a = null;
+            }(a.q)) {
+                a.r;
+                console.log("FAIL");
+            }
+        } catch (e) {
+            console.log("PASS");
+        }
+    }
+    expect_stdout: "PASS"
+}