From c2174d06b28599944395d75e10a5d77d79fd3ede Mon Sep 17 00:00:00 2001
From: alexlamsl <alexlamsl@gmail.com>
Date: Fri, 16 Jun 2017 15:16:33 +0800
Subject: [PATCH] in-place `dead_code`

---
 lib/compress.js | 54 +++++++++++++++++++++++++------------------------
 1 file changed, 28 insertions(+), 26 deletions(-)

diff --git a/lib/compress.js b/lib/compress.js
index 469ba980..3231ffc2 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -670,7 +670,7 @@ merge(Compressor.prototype, {
             CHANGED = false;
             statements = eliminate_spurious_blocks(statements);
             if (compressor.option("dead_code")) {
-                statements = eliminate_dead_code(statements, compressor);
+                eliminate_dead_code(statements, compressor);
             }
             if (compressor.option("if_return")) {
                 statements = handle_if_return(statements, compressor);
@@ -1062,35 +1062,37 @@ merge(Compressor.prototype, {
         };
 
         function eliminate_dead_code(statements, compressor) {
-            var has_quit = false;
-            var orig = statements.length;
+            var has_quit;
             var self = compressor.self();
-            statements = statements.reduce(function(a, stat){
-                if (has_quit) {
-                    extract_declarations_from_unreachable_code(compressor, stat, a);
-                } else {
-                    if (stat instanceof AST_LoopControl) {
-                        var lct = compressor.loopcontrol_target(stat);
-                        if ((stat instanceof AST_Break
-                             && !(lct instanceof AST_IterationStatement)
-                             && loop_body(lct) === self) || (stat instanceof AST_Continue
-                                                             && loop_body(lct) === self)) {
-                            if (stat.label) {
-                                remove(stat.label.thedef.references, stat);
-                            }
-                        } else {
-                            a.push(stat);
+            for (var i = 0, n = 0, len = statements.length; i < len; i++) {
+                var stat = statements[i];
+                if (stat instanceof AST_LoopControl) {
+                    var lct = compressor.loopcontrol_target(stat);
+                    if (stat instanceof AST_Break
+                            && !(lct instanceof AST_IterationStatement)
+                            && loop_body(lct) === self
+                        || stat instanceof AST_Continue
+                            && loop_body(lct) === self) {
+                        if (stat.label) {
+                            remove(stat.label.thedef.references, stat);
                         }
                     } else {
-                        a.push(stat);
+                        statements[n++] = stat;
                     }
-                    if (aborts(stat)) has_quit = true;
+                } else {
+                    statements[n++] = stat;
                 }
-                return a;
-            }, []);
-            CHANGED = statements.length != orig;
-            return statements;
-        };
+                if (aborts(stat)) {
+                    has_quit = statements.slice(i + 1);
+                    break;
+                }
+            }
+            statements.length = n;
+            CHANGED = n != len;
+            if (has_quit) has_quit.forEach(function(stat) {
+                extract_declarations_from_unreachable_code(compressor, stat, statements);
+            });
+        }
 
         function sequencesize(statements, compressor) {
             if (statements.length < 2) return;
@@ -1117,7 +1119,7 @@ merge(Compressor.prototype, {
             statements.length = n;
             sequencesize_2(statements, compressor);
             CHANGED = statements.length != len;
-        };
+        }
 
         function sequencesize_2(statements, compressor) {
             function cons_seq(right) {