improve transversal efficiency in `collapse_vars` (#2611)

fixes #2603

1 files changed, 40 insertions, 21 deletions

diff --git a/lib/compress.js b/lib/compress.js
index bccd7630..52c30964 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -905,10 +905,18 @@ merge(Compressor.prototype, {
                 if (abort) return node;
                 // Scan case expressions first in a switch statement
                 if (node instanceof AST_Switch) {
+                    if (!hit) {
+                        if (node !== hit_stack[hit_index]) return node;
+                        hit_index++;
+                    }
                     node.expression = node.expression.transform(scanner);
                     for (var i = 0, len = node.body.length; !abort && i < len; i++) {
                         var branch = node.body[i];
                         if (branch instanceof AST_Case) {
+                            if (!hit) {
+                                if (branch !== hit_stack[hit_index]) continue;
+                                hit_index++;
+                            }
                             branch.expression = branch.expression.transform(scanner);
                             if (side_effects || !replace_all) break;
                         }
@@ -918,13 +926,13 @@ merge(Compressor.prototype, {
                 }
                 // Skip nodes before `candidate` as quickly as possible
                 if (!hit) {
-                    if (node === candidate) {
-                        hit = true;
-                        stop_after = find_stop(node, 0);
-                        if (stop_after === node) abort = true;
-                        return node;
-                    }
-                    return;
+                    if (node !== hit_stack[hit_index]) return node;
+                    hit_index++;
+                    if (hit_index < hit_stack.length) return;
+                    hit = true;
+                    stop_after = find_stop(node, 0);
+                    if (stop_after === node) abort = true;
+                    return node;
                 }
                 // Stop immediately if these node types are encountered
                 var parent = scanner.parent();
@@ -1013,11 +1021,11 @@ merge(Compressor.prototype, {
                 if (abort) return node;
                 // Skip nodes before `candidate` as quickly as possible
                 if (!hit) {
-                    if (node === candidate) {
-                        hit = true;
-                        return node;
-                    }
-                    return;
+                    if (node !== hit_stack[hit_index]) return node;
+                    hit_index++;
+                    if (hit_index < hit_stack.length) return;
+                    hit = true;
+                    return node;
                 }
                 // Replace variable when found
                 if (node instanceof AST_SymbolRef
@@ -1038,9 +1046,12 @@ merge(Compressor.prototype, {
                 //   var a = x(), b = undefined;
                 if (stat_index == 0 && compressor.option("unused")) extract_args();
                 // Find collapsible assignments
+                var hit_stack = [];
                 extract_candidates(statements[stat_index]);
                 while (candidates.length > 0) {
-                    var candidate = candidates.pop();
+                    hit_stack = candidates.pop();
+                    var hit_index = 0;
+                    var candidate = hit_stack[hit_stack.length - 1];
                     var value_def = null;
                     var stop_after = null;
                     var lhs = get_lhs(candidate);
@@ -1074,6 +1085,7 @@ merge(Compressor.prototype, {
                         if (abort && def.references.length - def.replaced > replaced) replaced = false;
                         else {
                             abort = false;
+                            hit_index = 0;
                             hit = funarg;
                             for (var i = stat_index; !abort && i < statements.length; i++) {
                                 statements[i].transform(multi_replacer);
@@ -1124,18 +1136,24 @@ merge(Compressor.prototype, {
                             });
                             arg.walk(tw);
                         }
-                        if (arg) candidates.unshift(make_node(AST_VarDef, sym, {
+                        if (arg) candidates.unshift([ make_node(AST_VarDef, sym, {
                             name: sym,
                             value: arg
-                        }));
+                        }) ]);
                     }
                 }
             }
 
             function extract_candidates(expr) {
-                if (expr instanceof AST_Assign && !expr.left.has_side_effects(compressor)
-                    || expr instanceof AST_Unary && (expr.operator == "++" || expr.operator == "--")) {
-                    candidates.push(expr);
+                hit_stack.push(expr);
+                if (expr instanceof AST_Assign) {
+                    if (!expr.left.has_side_effects(compressor)) {
+                        candidates.push(hit_stack.slice());
+                    }
+                } else if (expr instanceof AST_Unary) {
+                    if (expr.operator == "++" || expr.operator == "--") {
+                        candidates.push(hit_stack.slice());
+                    }
                 } else if (expr instanceof AST_Call) {
                     extract_candidates(expr.expression);
                     expr.args.forEach(extract_candidates);
@@ -1146,9 +1164,7 @@ merge(Compressor.prototype, {
                     extract_candidates(expr.consequent);
                     extract_candidates(expr.alternative);
                 } else if (expr instanceof AST_Definitions) {
-                    expr.definitions.forEach(function(var_def) {
-                        if (var_def.value) candidates.push(var_def);
-                    });
+                    expr.definitions.forEach(extract_candidates);
                 } else if (expr instanceof AST_Exit) {
                     if (expr.value) extract_candidates(expr.value);
                 } else if (expr instanceof AST_For) {
@@ -1162,7 +1178,10 @@ merge(Compressor.prototype, {
                 } else if (expr instanceof AST_Switch) {
                     extract_candidates(expr.expression);
                     expr.body.forEach(extract_candidates);
+                } else if (expr instanceof AST_VarDef) {
+                    if (expr.value) candidates.push(hit_stack.slice());
                 }
+                hit_stack.pop();
             }
 
             function find_stop(node, level) {