fix(asm): carry the arm64 immediate to ZR through MOVZ

Assisted-by: GLM 5.3 Flash

asm/arm64_assemble.go

@@ -1820,7 +1820,10 @@ func encodeARM64LoadImm(rd int, v int64, mnem string) ([]byte, error) {
 	//   `MOVD $4096, R27` is ORR $4096, not MOVZ $(1<<12)
 	// - outside that band: MOVZ/MOVN first (C_MOVCON before C_BITCON), and
 	//   negative values reach MOVN before the bitmask test
-	tryBitmaskFirst := d > 0 && (d <= 0xFFF || (d&0xFFF == 0 && d <= 0xFFF000))
+	// The bitmask path exists only for a real register: omovconst guards it
+	// with rt != REGZERO, so an immediate to ZR always rides the MOVZ/MOVN
+	// sequence carrying the value.
+	tryBitmaskFirst := rd != 31 && d > 0 && (d <= 0xFFF || (d&0xFFF == 0 && d <= 0xFFF000))
 
 	if tryBitmaskFirst {
 		// Addcon-band immediate: try bitmask first (Go uses ORR for values
@@ -1849,7 +1852,7 @@ func encodeARM64LoadImm(rd int, v int64, mnem string) ([]byte, error) {
 	}
 
 	// For values outside the bitmask-first range that are not movcon: try bitmask.
-	if !tryBitmaskFirst {
+	if !tryBitmaskFirst && rd != 31 {
 		N, immr, imms, ok := arm64Bitmask(uint64(d), int(sf))
 		if ok {
 			return a64wordLE(sf<<31 | 1<<29 | 0x24<<23 | N<<22 | immr<<16 | imms<<10 | 31<<5 | uint32(rd)), nil