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Joe Savona
8ada08f11e
Ports constant propagation to Rust. The algorithm is broadly similar to the TS version, and most of the differences come from the slightly different HIR data model (operands are instruction indices not identifier ids). What this means is that the Constants map that we build up is really only used for variables that existed in the original program, and only comes into play with instructions like LoadLocal and StoreLocal. Other instructions such as Binary just look up their operands directly, ie they load the referenced instruction to check if both left/right are primitives. Note that with SSA form and the index-based operands we could actually get rid of StoreLocal/LoadLocal completely, which would further simplify constant propagation. However: * we'd need to add a Phi instruction kind, not a big deal but it diverges even more * more importantly, it makes it super hard to implement LeaveSSA That second point is a deal-breaker so unless someone has a great idea for how to exit SSA form without having Load/Stores, let's keep them.