If anything this paper is unfair to the native compiler; they compare V8 and SpiderMonkey from April 2019 to a clang release from March 2017, and they turn off

If anything this paper is unfair to the native compiler; they compare V8 and SpiderMonkey from April 2019 to a clang release from March 2017, and they turn off autovectorization. That being said, most of the slowdowns they identify seem to be deficiencies in the WASM engines rather than fundamental problems with WASM itself.