The　programmable　switch　offers　a　limited　capacity　of　packet　header　vector　(PHV)　words　that　store　packet　header　fields　and　metadata　fields　defined　by　network　functions.　However,　existing　switch　compilers　employ　inefficient　strategies　of　encoding　fields　on　PHV　words.　Their　encoding　wastes　scarce　PHV　words　and　may　result　in　failures　when　deploying　network　functions.　In　this　paper,　we　propose　Melody,　a　new　framework　that　reuses　PHV　words　for　as　many　fields　as　possible　to　achieve　resource-efficient　PHV　encoding.　Melody　offers　a　field　analyzer　and　an　optimization　framework.　The　analyzer　identifies　which　fields　can　reuse　PHV　words　while　preserving　the　original　packet　processing　logic.　The　framework　integrates　analysis　results　into　its　encoding　to　offer　the　resource-optimal　decisions.　We　evaluate　Melody　with　production-scale　network　functions.　Our　results　show　that　Melody　reduces　the　consumption　of　PHV　words　by　up　to　85%.　©　2023　IEEE.