Compress conditional assignments where all possible outcomes are equivalant and condition has no side effects

2 files changed, 51 insertions, 0 deletions

diff --git a/lib/compress.js b/lib/compress.js
index b55361b3..e493e5fe 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -2321,6 +2321,13 @@ merge(Compressor.prototype, {
                 alternative: alternative
             });
         }
+        // x=y?1:1 --> x=1
+        if (!self.condition.has_side_effects(compressor)
+            && consequent instanceof AST_Constant
+            && alternative instanceof AST_Constant
+            && consequent.equivalent_to(alternative)) {
+            return make_node_from_constant(compressor, consequent.value, self);
+        }
         return self;
     });
 
diff --git a/test/compress/conditionals.js b/test/compress/conditionals.js
index 213b246b..b0234031 100644
--- a/test/compress/conditionals.js
+++ b/test/compress/conditionals.js
@@ -232,3 +232,47 @@ cond_5: {
         some_condition() && some_other_condition() && do_something();
     }
 }
+
+cond_7: {
+    options = {
+        conditionals: true,
+        evaluate    : true
+    };
+    input: {
+        // compress these
+        if (y) {
+            x = 1+1;
+        } else {
+            x = 2;
+        }
+
+        x = y ? 'foo' : 'fo'+'o';
+
+        x = y ? 'foo' : y ? 'foo' : 'fo'+'o';
+
+        // don't compress these
+        x = y ? a : b;
+
+        x = y ? 'foo' : 'fo';
+
+        // make sure not to mess with conditions that have side effects
+        // TODO: Make sure to mess with conditions that have side effects... proprely
+        if (some_condition()) {
+            x = 1+1;
+        } else {
+            x = 2;
+        }
+
+        x = some_condition() ? 'foo' : 'fo'+'o';
+    }
+    expect: {
+        x = 2;
+        x = 'foo';
+        x = 'foo';
+        x = y ? a : b;
+        x = y ? 'foo' : 'fo';
+        x = some_condition() ? 2 : 2;
+        x = some_condition() ? 'foo' : 'foo';
+    }
+}
+