Module x64asm 

A minimal x86-64 instruction encoder for the contiguous register-allocated region backend (compile_region_regalloc).

This is deliberately tiny: it covers exactly the instruction shapes the linear-scan int backend emits — register/immediate moves, the three-operand arithmetic the allocator lowers (via a two-address dst = lhs; dst OP rhs discipline), compares + setcc, conditional and unconditional jumps with late-bound labels, frame loads/stores (base + disp), prologue/epilogue register save/restore, and ret. It is NOT a general assembler.

Register numbering follows the hardware encoding (rax=0 … r15=15); the REX prefix and ModRM/SIB bytes are emitted directly. All emitted code is position-independent except the jcc/jmp displacements, which are resolved against final offsets by Asm::resolve before the bytes leave this module.

Structs

Asm

The x86-64 byte emitter with late-bound labels.

LabelId

A label in the instruction stream. Created with Asm::new_label, its position fixed with Asm::bind, and referenced by jumps; all references are patched in Asm::resolve.

Enums

Cond

An integer condition, mapping to an x86 condition code. The first six are SIGNED; Cond::AeU is the one UNSIGNED code the array bounds check needs (jae — “above or equal”, unsigned >=), used so a 1-based index whose idx - 1 wraps negative (e.g. index 0) trips the OOB exit, matching the stencil’s (im1 as u64) >= (len as u64) guard.

Reg

A hardware general-purpose register, by its 4-bit encoding.

Xmm

A hardware XMM register (SSE2), by its 4-bit encoding. f64 slots that win a physical register live here for the whole function (a SECOND register class alongside the GP Reg one); the rest spill to the frame. All XMM registers are caller-saved under SysV, so none need save/restore in the prologue.