# Compute the first phase of SSA algorithm: placing phi-functions
	fun compute_phi(ssa: SSA)
	do
		var root_block = basic_block.as(not null)

		# Compute the iterated dominance frontier of the graph of basic blocks
		root_block.compute_df

		# Places where a phi-function is added per variable
		var phi_blocks = new HashMap[Variable, Array[BasicBlock]]

		# For each variables in the propdef
		for v in variables do
			var phi_variables = new Array[BasicBlock]

			var read_blocks = new Array[BasicBlock]
			read_blocks.add_all(v.read_blocks)
			read_blocks.add_all(v.assignment_blocks)

			# While we have not treated each part accessing `v`
			while not read_blocks.is_empty do
				# Remove a block from the array
				var block = read_blocks.shift

				# For each block in the dominance frontier of `block`
				for df in block.dominance_frontier do
					# If we have not yet put a phi-function at the beginning of this block
					if not phi_variables.has(df) then
						phi_variables.add(df)

						# Create a new phi-function and set its dependences
						var phi = new PhiFunction("phi", df)
						phi.add_dependences(df, v)
						phi.block = df
						phi.original_variable = phi
						phi.declared_type = v.declared_type

						# Indicate this phi-function is assigned in this block
						phi.assignment_blocks.add(block)
						ssa.phi_functions.add(phi)

						# Add a phi-function at the beginning of df for variable v
						df.phi_functions.add(phi)

						if not v.read_blocks.has(df) or not v.assignment_blocks.has(df) then read_blocks.add(df)
					end
				end
			end

			# Add `phi-variables` to the global map
			phi_blocks[v] = phi_variables
		end
	end