fix LHS cases for NaN & friends (#1804)

`Infinity = beyond` should not become `1/0 = beyond`

1 files changed, 15 insertions, 20 deletions

diff --git a/lib/compress.js b/lib/compress.js
index 5b405ec1..1d9258cf 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -404,7 +404,7 @@ merge(Compressor.prototype, {
 
         function is_modified(node, level, func) {
             var parent = tw.parent(level);
-            if (isLHS(node, parent)
+            if (is_lhs(node, parent)
                 || !func && parent instanceof AST_Call && parent.expression === node) {
                 return true;
             } else if (parent instanceof AST_PropAccess && parent.expression === node) {
@@ -697,7 +697,7 @@ merge(Compressor.prototype, {
             return statements;
 
             function is_lvalue(node, parent) {
-                return node instanceof AST_SymbolRef && isLHS(node, parent);
+                return node instanceof AST_SymbolRef && is_lhs(node, parent);
             }
             function replace_var(node, parent, is_constant) {
                 if (is_lvalue(node, parent)) return node;
@@ -1299,9 +1299,9 @@ merge(Compressor.prototype, {
 
     var unary_side_effects = makePredicate("delete ++ --");
 
-    function isLHS(node, parent) {
-        return parent instanceof AST_Unary && unary_side_effects(parent.operator)
-            || parent instanceof AST_Assign && parent.left === node;
+    function is_lhs(node, parent) {
+        if (parent instanceof AST_Unary && unary_side_effects(parent.operator)) return parent.expression;
+        if (parent instanceof AST_Assign && parent.left === node) return node;
     }
 
     (function (def){
@@ -1314,7 +1314,7 @@ merge(Compressor.prototype, {
                     node = parent;
                     parent = compressor.parent(level++);
                 } while (parent instanceof AST_PropAccess && parent.expression === node);
-                if (isLHS(node, parent)) {
+                if (is_lhs(node, parent)) {
                     compressor.warn('global_defs ' + this.print_to_string() + ' redefined [{file}:{line},{col}]', this.start);
                 } else {
                     return def;
@@ -3620,12 +3620,8 @@ merge(Compressor.prototype, {
         return self;
     });
 
-    function in_delete(parent) {
-        return parent instanceof AST_UnaryPrefix && parent.operator == "delete";
-    }
-
-    function is_atomic(parent, self) {
-        return parent.expression instanceof AST_SymbolRef || parent.expression.TYPE === self.TYPE;
+    function is_atomic(lhs, self) {
+        return lhs instanceof AST_SymbolRef || lhs.TYPE === self.TYPE;
     }
 
     OPT(AST_Undefined, function(self, compressor){
@@ -3641,8 +3637,8 @@ merge(Compressor.prototype, {
                 return ref;
             }
         }
-        var parent = compressor.parent();
-        if (in_delete(parent) && is_atomic(parent, self)) return self;
+        var lhs = is_lhs(compressor.self(), compressor.parent());
+        if (lhs && is_atomic(lhs, self)) return self;
         return make_node(AST_UnaryPrefix, self, {
             operator: "void",
             expression: make_node(AST_Number, self, {
@@ -3652,11 +3648,10 @@ merge(Compressor.prototype, {
     });
 
     OPT(AST_Infinity, function(self, compressor){
-        var parent = compressor.parent();
-        var del = in_delete(parent);
-        if (del && is_atomic(parent, self)) return self;
+        var lhs = is_lhs(compressor.self(), compressor.parent());
+        if (lhs && is_atomic(lhs, self)) return self;
         if (compressor.option("keep_infinity")
-            && !(del && !is_atomic(parent, self))
+            && !(lhs && !is_atomic(lhs, self))
             && !find_variable(compressor, "Infinity"))
             return self;
         return make_node(AST_Binary, self, {
@@ -3671,8 +3666,8 @@ merge(Compressor.prototype, {
     });
 
     OPT(AST_NaN, function(self, compressor){
-        var parent = compressor.parent();
-        if (in_delete(parent) && !is_atomic(parent, self)
+        var lhs = is_lhs(compressor.self(), compressor.parent());
+        if (lhs && !is_atomic(lhs, self)
             || find_variable(compressor, "NaN")) {
             return make_node(AST_Binary, self, {
                 operator: "/",