ref: f2e04e5f2f85f9dda6d813a9a47a95995de1e5aa dir: /src/cmd/as/target/x86/rules.dat/
reg8 AREG_R8CLASS reg16 AREG_R16CLASS reg32 AREG_R32CLASS imm8 AIMM8 imm16 AIMM16 imm32 AIMM32 imm64 AIMM64 \(n\) ADIRECT sym ASYM string ASTR