From e23bf480522e64db43f8764fef64312750c58e77 Mon Sep 17 00:00:00 2001
From: "Alex Lam S.L" <alexlamsl@gmail.com>
Date: Sun, 10 May 2020 20:08:05 +0100
Subject: enhance `evaluate` & `reduce_vars` (#3873)

---
 lib/compress.js | 26 ++++++++++++++++++++------
 1 file changed, 20 insertions(+), 6 deletions(-)

(limited to 'lib')

diff --git a/lib/compress.js b/lib/compress.js
index 6a444e92..fcbbffb3 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -492,8 +492,7 @@ merge(Compressor.prototype, {
         function ref_once(tw, compressor, def) {
             return compressor.option("unused")
                 && !def.scope.pinned()
-                && def.references.length - def.recursive_refs == 1
-                && tw.loop_ids[def.id] === tw.in_loop;
+                && def.references.length - def.recursive_refs == 1;
         }
 
         function is_immutable(value) {
@@ -797,8 +796,9 @@ merge(Compressor.prototype, {
                 if (recursive) {
                     d.recursive_refs++;
                 } else if (value && ref_once(tw, compressor, d)) {
+                    d.in_loop = tw.loop_ids[d.id] !== tw.in_loop;
                     d.single_use = value instanceof AST_Lambda && !value.pinned()
-                        || d.scope === this.scope && value.is_constant_expression();
+                        || !d.in_loop && d.scope === this.scope && value.is_constant_expression();
                 } else {
                     d.single_use = false;
                 }
@@ -3501,7 +3501,21 @@ merge(Compressor.prototype, {
                 if (fn.name && fn.name.definition().recursive_refs > 0) return this;
                 if (this.is_expr_pure(compressor)) return this;
                 var stat = fn.first_statement();
-                if (!(stat instanceof AST_Return)) return this;
+                if (!(stat instanceof AST_Return)) {
+                    if (ignore_side_effects) {
+                        var found = false;
+                        fn.walk(new TreeWalker(function(node) {
+                            if (found) return true;
+                            if (node instanceof AST_Return) {
+                                if (node.value && node.value.evaluate(compressor, true) !== undefined) found = true;
+                                return true;
+                            }
+                            if (node instanceof AST_Scope && node !== fn) return true;
+                        }));
+                        if (!found) return void 0;
+                    }
+                    return this;
+                }
                 var args = eval_args(this.args);
                 if (!args) return this;
                 if (!stat.value) return undefined;
@@ -7427,7 +7441,7 @@ merge(Compressor.prototype, {
             var single_use = def.single_use && !(parent instanceof AST_Call && parent.is_expr_pure(compressor));
             if (single_use) {
                 if (fixed instanceof AST_Lambda) {
-                    if (def.scope !== self.scope
+                    if ((def.scope !== self.scope || def.in_loop)
                         && (!compressor.option("reduce_funcs") || def.escaped.depth == 1 || fixed.inlined)) {
                         single_use = false;
                     } else if (recursive_ref(compressor, def)) {
@@ -7771,7 +7785,7 @@ merge(Compressor.prototype, {
             expressions.push(self);
             return make_sequence(self, expressions);
         }
-        var condition = self.condition.is_truthy() || self.condition.evaluate(compressor);
+        var condition = self.condition.is_truthy() || self.condition.evaluate(compressor, true);
         if (!condition) {
             AST_Node.warn("Condition always false [{file}:{line},{col}]", self.start);
             return make_sequence(self, [ self.condition, self.alternative ]).optimize(compressor);
-- 
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