Documentation

Inline definitions into their call sites: all of them when flatten, otherwise those used at most once. Definitions referenced as extern models are never inlined (the reference is by name), and neither are defns marked noinline -- the pin wins over --flatten, so a noinline defn is always findable as a module in the output. The inlined-away defns are removed by the final purge; a follow-up partialEval fuses the slice/concat plumbing exposed by inlining and drops the argument wires that fusion leaves unused.

Inline definitions satisfying the predicate into their call sites.

Drop defns unreachable from the device body (following calls and the models of called externs) and extern decls that are never referenced. Not gated on noinline: pinning affects inlining, not liveness, so dead pinned defns don't accumulate.

Constant folding and wire fusion. Primitives, muxes, slices, and concatenations of literals fold via the interpreter's own evaluator; calls (and extern calls with models) whose arguments are all literals evaluate fully. Lets bound to atomic expressions (literals, variables, don't-cares) substitute away; lets bound to pure wiring (slices and concatenations of atoms) are fused through where they are sliced, so slice-of-concat plumbing simplifies across named wires (both expression lets and device-level wires). Unused expression lets are dropped here; unused device wires are dropped by purgeDevLets.

Drop device wires (SLets) never read by a later statement (fusion in partialEval is what strands them).

Drop zero-width parameters (and the corresponding arguments at call sites) and zero-width-result defns (calls to them become nil).

Redirect calls to definitions with identical signatures and bodies to a single representative. Should be followed by purgeUnused. Defns marked noinline are name-pinned: they take no part in merging (neither as survivors nor as redirected losers). Each survivor records the losers redirected to it with an appended "also: ..." doc line.

The standard optimization pipeline, iterated to a fixpoint (bounded by the --rtl-opt level).

Defns containing (transitively) calls to sequential externs are inlined into the device body; sequential-extern calls in the device body then become instances: nested lets are flattened to device-level lets (sound: the language is pure and total) and each seq-XCall is replaced by the concatenation of a fresh instance's output ports, with its inputs driven from the call's arguments.