feat(amd64): encode the GOROOT instruction families

Assisted-by: GLM 5.3 Flash

testdata/verify/atomics_amd64.s

@@ -0,0 +1,69 @@
+// Atomics and carry-extending multi-word arithmetic: exchange,
+// compare-exchange, exchange-add, ADCX/ADOX and the CRC-32 accumulator
+// family.  Every result is folded back so no instruction is dead.
+
+#include "textflag.h"
+
+// func xchg(p *uint64, v uint64) uint64
+TEXT ·xchg(SB), NOSPLIT, $0-24
+	MOVQ  p+0(FP), AX
+	MOVQ  v+8(FP), BX
+	XCHGQ BX, (AX)
+	XCHGQ BX, CX
+	XCHGL BX, CX
+	XCHGW BX, CX
+	XCHGB BL, CL
+	MOVQ  AX, ret+16(FP)
+	RET
+
+// func cmpxchg(p *uint64, old, new uint64) uint8
+TEXT ·cmpxchg(SB), NOSPLIT, $0-25
+	MOVQ     p+0(FP), AX
+	MOVQ     old+8(FP), BX
+	MOVQ     new+16(FP), CX
+	CMPXCHGQ CX, (AX)
+	CMPXCHGL CX, BX
+	CMPXCHGW CX, BX
+	CMPXCHGB CL, BL
+	SETEQ    AL
+	MOVB     AL, ret+24(FP)
+	RET
+
+// func xadd(p *uint64, v uint64) uint64
+TEXT ·xadd(SB), NOSPLIT, $0-24
+	MOVQ  p+0(FP), AX
+	MOVQ  v+8(FP), BX
+	XADDQ BX, (AX)
+	XADDL BX, CX
+	XADDW BX, CX
+	XADDB BL, CL
+	MOVQ  AX, ret+16(FP)
+	RET
+
+// func adcx_adox(lo, hi, x, y uint64) uint64
+TEXT ·adcx_adox(SB), NOSPLIT, $0-40
+	MOVQ  lo+0(FP), AX
+	MOVQ  hi+8(FP), DX
+	MOVQ  x+16(FP), BX
+	MOVQ  y+24(FP), CX
+	ADCXQ BX, AX
+	ADOXQ CX, DX
+	ADCXL BX, AX
+	ADOXL CX, DX
+	XORQ  BX, BX
+	ADCXQ BX, AX
+	MOVQ  AX, ret+32(FP)
+	RET
+
+// func crc32(crc uint32, p *byte, n int) uint32
+TEXT ·crc32(SB), NOSPLIT, $0-28
+	MOVL   crc+0(FP), AX
+	MOVQ   p+8(FP), SI
+	MOVQ   n+16(FP), CX
+	CRC32B (SI), AX
+	CRC32Q (SI), CX
+	CRC32L (SI), AX
+	MOVW   (SI), DX
+	CRC32W DX, AX
+	MOVL   AX, ret+24(FP)
+	RET