Discharge fails if any indices have been invalidated.

[UnsignedByte]

Discharge works with DenseIndexInfos, meaning if any parameters/events/ports have been invalidated before discharge this throws an error. The culprit is here:

filament/crates/filament/src/ir_passes/discharge.rs

Lines 591 to 608 in 2fe2b31

	for (idx, _) in data.comp.params().iter() {
	let sexp = self
	.sol
	.declare_fun(self.fmt_param(idx, comp), vec![], int)
	.unwrap();
	self.overflow_assert(sexp);
	self.param_map.push(idx, sexp);
	}
	// Declare all events
	for (idx, _) in data.comp.events().iter() {
	let sexp = self
	.sol
	.declare_fun(self.fmt_event(idx, comp), vec![], int)
	.unwrap();
	self.overflow_assert(sexp);
	self.ev_map.push(idx, sexp);
	}

This causes issues because .ports and .events automatically only iterate over valid indices. We can solve this in two ways:

• Some sort of "cleanup" pass that removes invalid indices (likely having to reconstruct the entire IR)
• Change .push to extend the DenseIndexInfo by default. This does not work in the case of discharge though, where SExpr is not Default.

[UnsignedByte]

Just realized that insert already accomplishes this for Default stores.

[UnsignedByte]

Even larger issue now is that Exprs can exist that refer to invalid parameters that have been deleted... Classic dangling pointers.

[rachitnigam]

Yup, arena allocators are hard... Maybe time to switch to a crate for this or something.

[UnsignedByte]

How exactly would this solve the Expr dangling pointer issue? I looked at a few arena allocators (such as kioku) but I am not sure exactly how they might be relevant.