feat[venom]: add store elimination pass

[harkal]

What I did

I added a new pass the eliminates venom store instructions. These instructions have no equivalent in the generated code, and serve the venom code temporarily. Removing them and forwarding the results to the actual uses, helps with further optimizations.

How I did it

How to verify it

Commit message

Venom uses the `store` instruction to load a variable or literal to
another variable. This commit adds a new pass `StoreElimination` that
forwards the rhs for `store`s to their uses, eliminating the `store`
instruction in the process.

Description for the changelog

Cute Animal Picture

[charles-cooper]

this looks like duplication (or evolution) of

vyper/vyper/venom/passes/sccp/sccp.py

Lines 330 to 348 in ea1e4ea

	def _propagate_variables(self):
	"""
	Copy elimination. #NOTE: Not working yet, but it's also not needed atm.
	"""
	for bb in self.dom.dfs_walk:
	for inst in bb.instructions:
	if inst.opcode == "store":
	uses = self._get_uses(inst.output)
	remove_inst = True
	for usage_inst in uses:
	if usage_inst.opcode == "phi":
	remove_inst = False
	continue
	for i, op in enumerate(usage_inst.operands):
	if op == inst.output:
	usage_inst.operands[i] = inst.operands[0]
	if remove_inst:
	inst.opcode = "nop"
	inst.operands = []

. maybe that is dead code, and it can be removed now?

[charles-cooper]

just checked and this looks like it reduces instructions by 1.6% and 1.9% on CurveStableSwapNG.vy and CurveCryptoMathOptimized.vy, respectively