implement function inlining (#2053)

- empty body
- single `AST_Return`
- single `AST_SimpleStatement`
- avoid `/*#__PURE__*/`

Miscellaneous
- enhance single-use function substitution

fixes #281

1 files changed, 1 insertions, 1 deletions

diff --git a/test/compress/collapse_vars.js b/test/compress/collapse_vars.js
index 90d7ac93..158d1b4a 100644
--- a/test/compress/collapse_vars.js
+++ b/test/compress/collapse_vars.js
@@ -1146,7 +1146,7 @@ collapse_vars_constants: {
         function f3(x) {
             var b = x.prop;
             sideeffect1();
-            return b + -9;
+            return b + (function() { return -9; })();
         }
     }
 }