+/**
+ * Replace each register of type ATTR in this->instructions with a reference
+ * to a fixed HW register.
+ *
+ * If interleaved is true, then each attribute takes up half a register, with
+ * register N containing attribute 2*N in its first half and attribute 2*N+1
+ * in its second half (this corresponds to the payload setup used by geometry
+ * shaders in "single" or "dual instanced" dispatch mode). If interleaved is
+ * false, then each attribute takes up a whole register, with register N
+ * containing attribute N (this corresponds to the payload setup used by
+ * vertex shaders, and by geometry shaders in "dual object" dispatch mode).
+ */