Ligatures are affecting scroll performance

I am using the FiraCode font with macligatures set. When scrolling down, MacVim seems to hiccup a bit, but when I scroll up it is very smooth. When I do not set macligatures it scrolls fine (but doesn't show the cool characters). I am testing the scroll speed using both my touchpad and jk keys and my key repeat is set at 1 which is 15ms.

This was originally posted in FiraCode's issues, but the solution to the problem probably lies in improving macligatures support.

OSX 10.11, MacbookPro Retina

Followed the instructions to

set macligatures
set guifont=Fira\ Code:h12

Doing some dumb testing against Activity Monitor, it looks like the CPU load when I scroll down is much lower (~%60) than when I scroll up (150-200%), so the downscrolling seems to be inhibiting the scroll rather than taking on a huge CPU load and causing framerate hiccups.

Looking around for some possibly related topics:
Guy with the same issue (Scroll to Amadeus Demarzi)
thread related to listchars

まず、macOS 上の MacVim で Fira Code を使い、set macligatures と記載されている guifont 設定を使用して報告内容を再現し、その後、ligatures の有効時と無効時で上方向および下方向へのスクロールを比較します。背景を理解するため、リンクされている FiraCode issue と関連する listchars thread を読みます; macligatures を有効にしたときに、報告されている方向依存のスクロール速度低下が表示されなくなれば完了です。