migrate safe transformations out of unsafe_comps (#2962)

fixes #2959

README.md

@@ -605,8 +605,8 @@ If you're using the `X-SourceMap` header instead, you can just omit `sourceMap.u
   side effects permitting.
 
 - `comparisons` (default: `true`) -- apply certain optimizations to binary nodes,
-  e.g. `!(a <= b) → a > b` (only when `unsafe_comps`), attempts to negate binary
-  nodes, e.g. `a = !b && !c && !d && !e → a=!(b||c||d||e)` etc.
+  e.g. `!(a <= b) → a > b`, attempts to negate binary nodes, e.g.
+  `a = !b && !c && !d && !e → a=!(b||c||d||e)` etc.
 
 - `conditionals` (default: `true`) -- apply optimizations for `if`-s and conditional
   expressions
@@ -730,12 +730,8 @@ If you're using the `X-SourceMap` header instead, you can just omit `sourceMap.u
 
 - `unsafe` (default: `false`) -- apply "unsafe" transformations (discussion below)
 
-- `unsafe_comps` (default: `false`) -- Reverse `<` and `<=` to `>` and `>=` to
-  allow improved compression. This might be unsafe when an at least one of two
-  operands is an object with computed values due the use of methods like `get`,
-  or `valueOf`. This could cause change in execution order after operands in the
-  comparison are switching. Compression only works if both `comparisons` and
-  `unsafe_comps` are both set to true.
+- `unsafe_comps` (default: `false`) -- compress expressions like `a <= b` assuming
+  none of the operands can be (coerced to) `NaN`.
 
 - `unsafe_Function` (default: `false`) -- compress and mangle `Function(args, code)`
   when both `args` and `code` are string literals.

lib/compress.js

@@ -5041,11 +5041,9 @@ merge(Compressor.prototype, {
                 });
                 self = best_of(compressor, self, negated);
             }
-            if (compressor.option("unsafe_comps")) {
-                switch (self.operator) {
-                  case "<": reverse(">"); break;
-                  case "<=": reverse(">="); break;
-                }
+            switch (self.operator) {
+              case ">": reverse("<"); break;
+              case ">=": reverse("<="); break;
             }
         }
         if (self.operator == "+") {

test/compress/collapse_vars.js

@@ -913,15 +913,15 @@ collapse_vars_unary: {
             return delete x;
         }
         function f1(n) {
-            return n > +!!n
+            return +!!n < n;
         }
         function f2(n) {
             var k = 7;
-            return k--
+            return k--;
         }
         function f3(n) {
             var k = 7;
-            return ++k
+            return ++k;
         }
         function f4(n) {
             var k = 8 - n;

test/compress/comparing.js

@@ -1,62 +1,42 @@
-keep_comparisons: {
+comparisons: {
     options = {
         comparisons: true,
-        unsafe_comps: false
     }
     input: {
-        var obj1 = {
-            valueOf: function() {triggeredFirst();}
-        }
-        var obj2 = {
-            valueOf: function() {triggeredSecond();}
-        }
+        var obj1, obj2;
         var result1 = obj1 <= obj2;
         var result2 = obj1 <  obj2;
         var result3 = obj1 >= obj2;
         var result4 = obj1 >  obj2;
     }
     expect: {
-        var obj1 = {
-            valueOf: function() {triggeredFirst();}
-        }
-        var obj2 = {
-            valueOf: function() {triggeredSecond();}
-        }
+        var obj1, obj2;
         var result1 = obj1 <= obj2;
         var result2 = obj1 <  obj2;
-        var result3 = obj1 >= obj2;
-        var result4 = obj1 >  obj2;
+        var result3 = obj2 <= obj1;
+        var result4 = obj2 <  obj1;
     }
 }
 
-keep_comparisons_with_unsafe_comps: {
+unsafe_comps: {
     options = {
         comparisons: true,
-        unsafe_comps: true
+        conditionals: true,
+        unsafe_comps: true,
     }
     input: {
-        var obj1 = {
-            valueOf: function() {triggeredFirst();}
-        }
-        var obj2 = {
-            valueOf: function() {triggeredSecond();}
-        }
-        var result1 = obj1 <= obj2;
-        var result2 = obj1 <  obj2;
-        var result3 = obj1 >= obj2;
-        var result4 = obj1 >  obj2;
+        var obj1, obj2;
+        obj1 <= obj2 ? f1() : g1();
+        obj1 <  obj2 ? f2() : g2();
+        obj1 >= obj2 ? f3() : g3();
+        obj1 >  obj2 ? f4() : g4();
     }
     expect: {
-        var obj1 = {
-            valueOf: function() {triggeredFirst();}
-        }
-        var obj2 = {
-            valueOf: function() {triggeredSecond();}
-        }
-        var result1 = obj2 >= obj1;
-        var result2 = obj2 >  obj1;
-        var result3 = obj1 >= obj2;
-        var result4 = obj1 >  obj2;
+        var obj1, obj2;
+        obj2 <  obj1 ? g1() : f1();
+        obj1 <  obj2 ? f2() : g2();
+        obj1 <  obj2 ? g3() : f3();
+        obj2 <  obj1 ? f4() : g4();
     }
 }
 

test/compress/if_return.js

@@ -243,7 +243,7 @@ issue_1089: {
     expect: {
         function x() {
             var f = document.getElementById("fname");
-            if (f.files[0].size > 12345)
+            if (12345 < f.files[0].size)
                 return alert("alert"), f.focus(), !1;
         }
     }