improve fix for #5917 (#5921)

Author: alexlamsl

lib/compress.js

@@ -601,6 +601,19 @@ 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) {
+                    var safe_ids = fixed.safe_ids;
+                    switch (safe_ids) {
+                      case null:
+                      case false:
+                        return;
+                      default:
+                        if (safe_ids && safe_ids.seq !== tw.safe_ids.seq) return;
+                    }
+                }
                 d.fixed = false;
             });
         }
@@ -648,6 +661,7 @@ Compressor.prototype.compress = function(node) {
             tw.defined_ids = defined_ids;
             var safe_ids = Object.create(tw.safe_ids);
             if (!sequential) safe_ids.seq = {};
+            if (conditional) safe_ids.cond = true;
             tw.safe_ids = safe_ids;
         }
 
@@ -1009,7 +1023,7 @@ Compressor.prototype.compress = function(node) {
                     walk_assign();
                     right.parent_scope.resolve().fn_defs.push(right);
                     right.safe_ids = null;
-                    if (!ld.fixed || !node.write_only) mark_fn_def(tw, ld, right);
+                    if (!ld.fixed || !node.write_only || tw.safe_ids.cond) mark_fn_def(tw, ld, right);
                     return true;
                 }
                 if (scan) {

test/compress/pure_getters.js

@@ -1716,7 +1716,7 @@ issue_5856: {
     expect_stdout: "PASS"
 }
 
-issue_5917: {
+issue_5917_1: {
     options = {
         pure_getters: "strict",
         reduce_vars: true,
@@ -1751,3 +1751,46 @@ issue_5917: {
     }
     expect_stdout: "PASS"
 }
+
+issue_5917_2: {
+    options = {
+        passes: 2,
+        pure_getters: "strict",
+        reduce_vars: true,
+        side_effects: true,
+        toplevel: true,
+    }
+    input: {
+        var b;
+        if (!console) {
+            b = function() {};
+            FAIL(f);
+        }
+        function f() {
+            b.p;
+        }
+        try {
+            f();
+            console.log("FAIL");
+        } catch (e) {
+            console.log("PASS");
+        }
+    }
+    expect: {
+        var b;
+        if (!console) {
+            b = function() {};
+            FAIL(f);
+        }
+        function f() {
+            b.p;
+        }
+        try {
+            f();
+            console.log("FAIL");
+        } catch (e) {
+            console.log("PASS");
+        }
+    }
+    expect_stdout: "PASS"
+}