avoid X-(-Y) in js optimizer; fixes #1685

4 files changed, 33 insertions, 5 deletions

diff --git a/tests/test_other.py b/tests/test_other.py
index 81221229..d4a5bb3a 100644
--- a/tests/test_other.py
+++ b/tests/test_other.py
@@ -1645,6 +1645,8 @@ f.close()
        ['asm', 'outline']),
       (path_from_root('tools', 'test-js-optimizer-asm-outline3.js'), open(path_from_root('tools', 'test-js-optimizer-asm-outline3-output.js')).read(),
        ['asm', 'outline']),
+      (path_from_root('tools', 'test-js-optimizer-asm-minlast.js'), open(path_from_root('tools', 'test-js-optimizer-asm-minlast-output.js')).read(),
+       ['asm', 'minifyWhitespace', 'last']),
     ]:
       print input
       output = Popen(listify(NODE_JS) + [path_from_root('tools', 'js-optimizer.js'), input] + passes, stdin=PIPE, stdout=PIPE).communicate()[0]
diff --git a/tools/js-optimizer.js b/tools/js-optimizer.js
index e5e0d287..022bdf47 100644
--- a/tools/js-optimizer.js
+++ b/tools/js-optimizer.js
@@ -3788,11 +3788,27 @@ function asmLastOpts(ast) {
           node[1] = simplifyNotCompsDirect(['unary-prefix', '!', conditionToBreak]);
           return node;
         }
-      } else if (type == 'binary' && node[1] == '&' && node[3][0] == 'unary-prefix' && node[3][1] == '-' && node[3][2][0] == 'num' && node[3][2][1] == 1) {
-        // Change &-1 into |0, at this point the hint is no longer needed
-        node[1] = '|';
-        node[3] = node[3][2];
-        node[3][1] = 0;
+      } else if (type == 'binary') {
+        if (node[1] === '&') {
+          if (node[3][0] === 'unary-prefix' && node[3][1] === '-' && node[3][2][0] === 'num' && node[3][2][1] === 1) {
+            // Change &-1 into |0, at this point the hint is no longer needed
+            node[1] = '|';
+            node[3] = node[3][2];
+            node[3][1] = 0;
+          }
+        } else if (node[1] === '-' && node[3][0] === 'unary-prefix') {
+          // avoid X - (-Y) because some minifiers buggily emit X--Y which is invalid as -- can be a unary. Transform to
+         //        X + Y
+          if (node[3][1] === '-') { // integer
+            node[1] = '+';
+            node[3] = node[3][2];
+          } else if (node[3][1] === '+') { // float
+            if (node[3][2][0] === 'unary-prefix' && node[3][2][1] === '-') {
+              node[1] = '+';
+              node[3][2] = node[3][2][2];
+            }
+          }
+        }
       }
     });
   });
diff --git a/tools/test-js-optimizer-asm-minlast-output.js b/tools/test-js-optimizer-asm-minlast-output.js
new file mode 100644
index 00000000..d25c6d9b
--- /dev/null
+++ b/tools/test-js-optimizer-asm-minlast-output.js
@@ -0,0 +1,2 @@
+function test($34){var $35=0;$35=$34+130.0;$35=$34+130;return $35|0}
+
diff --git a/tools/test-js-optimizer-asm-minlast.js b/tools/test-js-optimizer-asm-minlast.js
new file mode 100644
index 00000000..6d172899
--- /dev/null
+++ b/tools/test-js-optimizer-asm-minlast.js
@@ -0,0 +1,8 @@
+function test($34) {
+  var $35 = 0;
+  $35=($34)-((+-130));
+  $35=($34)-(-130);
+  return $35 | 0;
+}
+// EMSCRIPTEN_GENERATED_FUNCTIONS: ["test"]
+