GHC Core Optimisations
summary
Desugared System F–style Core appears as a small, explicitly typed IR where case drives evaluation; the talk traces specific passes (strictness/demand analysis, CPR, the worker/wrapper split, inlining and the Simplifier) and shows an example where optimisations cut allocations ~85% and speed doubles. A concrete patch implements common subexpression elimination to look through unfoldings, builds with Hadrian, and makes k collapse to the identity, but the fix exposes deeper interactions suggesting the proper repair belongs in the Simplifier rather than only CSE.
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chapters (7)
- 0:00GHC Core optimisations intro
- 1:10GHC Core pipeline basics
- 22:01Optimised Core performance
- 31:26GHC Core optimisations overview
- 50:55Local simplifier optimisations
- 1:01:59Demand analysis & worker/wrapper
- 1:16:10Fixing CSE bug
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