Simplified file structure

src/core/UsesRegister.go

@@ -0,0 +1,40 @@
+package core
+
+import (
+	"git.akyoto.dev/cli/q/src/ast"
+	"git.akyoto.dev/cli/q/src/cpu"
+	"git.akyoto.dev/cli/q/src/expression"
+)
+
+// UsesRegister returns true if evaluating the expression would write or read the given register.
+func (f *Function) UsesRegister(expr *expression.Expression, register cpu.Register) bool {
+	if expr.IsLeaf() {
+		return false
+	}
+
+	if ast.IsFunctionCall(expr) {
+		if register == f.CPU.Output[0] {
+			return true
+		}
+
+		for i, parameter := range expr.Children[1:] {
+			if register == f.CPU.Input[i] {
+				return true
+			}
+
+			if f.UsesRegister(parameter, register) {
+				return true
+			}
+		}
+
+		return false
+	}
+
+	for _, child := range expr.Children {
+		if f.UsesRegister(child, register) {
+			return true
+		}
+	}
+
+	return false
+}