nasm: Emit a16/a32 for useless address-size prefix#803
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Track whether the original encoding contained a 0x67 address-size prefix that had no semantic effect (i.e. the instruction has no memory operand). Backed by a free bit (bit 20) in InstrFlags1::flags1, following the same pattern as has_lock_prefix.
…0x67 OpCodeHandler_Prefix67 flips the address size and delegates to the real opcode handler. If the decoded instruction has no memory operand of any kind (OpKind >= MemorySegSI), the 0x67 byte had no semantic effect and was previously silently discarded. Record it via has_address_size_prefix so the encoder and formatters can reproduce the original bytes.
Extend write_prefixes() to emit the address-size prefix byte when instruction.has_address_size_prefix() is true, in addition to the existing EncoderFlags::P67 path that handles memory operands.
When has_address_size_prefix() is true and show_useless_prefixes is enabled, emit the NASM address-size keyword (a16 in 32-bit mode, a32 otherwise) so NASM can reproduce the original 0x67-prefixed bytes.
This was referenced Jun 12, 2026
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Summary
NasmFormatter::format_mnemonic(), emita16/a32wheninstruction.has_address_size_prefix()is true andshow_useless_prefixesis enabledDepends on: #802
Test plan
cargo test -p iced-x86passesshow_useless_prefixes=true:67 90(32-bit) formats asa16 nop