// Port of cmd/w6a/asm.c. Encoding subset matches what w6c emits — see
// cmd/w6a/asm.c for the authoritative list.

package w6a;

import os;
import rt;
import opcodes;
import strings;

export fn emitbyte(a: *asm_, b: u8) void = {
	if (a.textlen + 1u64 > a.textcap) {
		let nc: u64 = a.textcap;
		if (nc == 0u64) { nc = 4096u64; };
		nc = nc * 2u64;
		let nb: []u8 = alloc([], nc)!;
		let i: u64 = 0u64;
		for (i < a.textlen) { nb[i] = a.text[i]; i += 1u64; };
		a.text = nb.ptr;
		a.textcap = nc;
	};
	a.text[a.textlen] = b;
	a.textlen += 1u64;
};

export fn emitu32(a: *asm_, v: u32) void = {
	emitbyte(a, (v & 255u32): u8);
	emitbyte(a, ((v >> 8u32) & 255u32): u8);
	emitbyte(a, ((v >> 16u32) & 255u32): u8);
	emitbyte(a, ((v >> 24u32) & 255u32): u8);
};

export fn addreloc(a: *asm_, off: u64, kind: i32, s: *asym, add: i64) void = {
	let r: *areloc = alloc(areloc { off = off, section = 0, kind = kind, asy = s, addend = add, rnext = a.relocs })!;
	a.relocs = r;
};

// DATAR patches a 64-bit .data slot with a symbol's runtime VA;
// obj.ww separates section=1 relocs into .rela.data when emitting
// the .o.
export fn addrelocdata(a: *asm_, off: u64, kind: i32, s: *asym, add: i64) void = {
	let r: *areloc = alloc(areloc { off = off, section = 1, kind = kind, asy = s, addend = add, rnext = a.relocs })!;
	a.relocs = r;
};

export fn emitdatabyte(a: *asm_, b: u8) void = {
	if (a.datalen + 1u64 > a.datacap) {
		let nc: u64 = a.datacap;
		if (nc == 0u64) { nc = 256u64; };
		nc = nc * 2u64;
		let nb: []u8 = alloc([], nc)!;
		let i: u64 = 0u64;
		for (i < a.datalen) { nb[i] = a.data[i]; i += 1u64; };
		a.data = nb.ptr;
		a.datacap = nc;
	};
	a.data[a.datalen] = b;
	a.datalen += 1u64;
};

// Low 3 bits of register encoding.
fn rcode(r: i32) i32 = {
	if (r == D_AX) { return 0; };  if (r == D_CX) { return 1; };
	if (r == D_DX) { return 2; };  if (r == D_BX) { return 3; };
	if (r == D_SP) { return 4; };  if (r == D_BP) { return 5; };
	if (r == D_SI) { return 6; };  if (r == D_DI) { return 7; };
	if (r == D_R8)  { return 0; }; if (r == D_R9)  { return 1; };
	if (r == D_R10) { return 2; }; if (r == D_R11) { return 3; };
	if (r == D_R12) { return 4; }; if (r == D_R13) { return 5; };
	if (r == D_R14) { return 6; }; if (r == D_R15) { return 7; };
	if (r == D_X0) { return 0; };  if (r == D_X1) { return 1; };
	if (r == D_X2) { return 2; };  if (r == D_X3) { return 3; };
	if (r == D_X4) { return 4; };  if (r == D_X5) { return 5; };
	if (r == D_X6) { return 6; };  if (r == D_X7) { return 7; };
	if (r == D_X8)  { return 0; }; if (r == D_X9)  { return 1; };
	if (r == D_X10) { return 2; }; if (r == D_X11) { return 3; };
	if (r == D_X12) { return 4; }; if (r == D_X13) { return 5; };
	if (r == D_X14) { return 6; }; if (r == D_X15) { return 7; };
	return 0;
};

// 1 if r needs the REX high bit (R8..R15 or X8..X15).
fn rhi(r: i32) i32 = {
	if (r >= D_R8) { if (r <= D_R15) { return 1; }; };
	if (r >= D_X8) { if (r <= D_X15) { return 1; }; };
	return 0;
};

fn isxmm(r: i32) bool = {
	if (r >= D_X0) { if (r <= D_X15) { return true; }; };
	return false;
};

fn modrmbyte(mod: i32, reg: i32, rm: i32) u8 = {
	return (((mod & 3) << 6) | ((reg & 7) << 3) | (rm & 7)): u8;
};

// REX prefix; W=1 for 64-bit operand size.
fn emitrex(a: *asm_, regbit: i32, rmbit: i32, w: i32) void = {
	let b: u8 = 64u8;	// 0x40
	if (w != 0)      { b = b | 8u8; };
	if (regbit != 0) { b = b | 4u8; };
	if (rmbit != 0)  { b = b | 1u8; };
	if (b != 64u8) { emitbyte(a, b); }
	else { if (w != 0) { emitbyte(a, b); }; };
};

// 8-bit register operands: SPL/BPL/SIL/DIL exist only WITH a REX
// prefix — bare, codes 4-7 select AH/CH/DH/BH. Force the 0x40 byte
// when the named r8 is one of them.
fn emitrex8(a: *asm_, regbit: i32, rmbit: i32, r8: i32) void = {
	let b: u8 = 64u8;	// 0x40
	if (regbit != 0) { b = b | 4u8; };
	if (rmbit != 0)  { b = b | 1u8; };
	if (b != 64u8) { emitbyte(a, b); }
	else { if (rhi(r8) == 0 && rcode(r8) >= 4) { emitbyte(a, b); }; };
};

// ModR/M + (optional) SIB + displacement for [base+disp].
// Special-cases SP (needs SIB) and BP (forces explicit disp).
fn emitmodrmmem(a: *asm_, regfield: i32, base: i32, disp: i64) void = {
	let rm: i32 = rcode(base);
	let needsib: bool = (rm == 4);
	let forceddisp: bool = false;
	if (rm == 5) { if (disp == 0i64) { forceddisp = true; }; };

	let mod: i32 = 2;
	if (disp == 0i64) {
		if (!forceddisp) { mod = 0; }
		else { mod = 1; };
	} else {
		if (disp >= -128i64) { if (disp <= 127i64) { mod = 1; }; };
	};

	emitbyte(a, modrmbyte(mod, regfield, rm));
	if (needsib) {
		emitbyte(a, 36u8);	// 0x24: scale=0 idx=4(none) base=4
	};
	if (mod == 1) {
		emitbyte(a, (disp: u64 & 255u64): u8);
	} else { if (mod == 2) {
		emitu32(a, disp: u32);
	};};
};

// reg→reg "src, dst" generic encoding (89 /r, 01 /r, etc.).
fn encoderr(a: *asm_, opcode: u8, src: i32, dst: i32) void = {
	emitrex(a, rhi(src), rhi(dst), 1);
	emitbyte(a, opcode);
	emitbyte(a, modrmbyte(3, rcode(src), rcode(dst)));
};

// reg→mem(base, disp) (e.g. MOVQ src reg into mem; opcode = 0x89).
fn encoderm(a: *asm_, opcode: u8, srcreg: i32, base: i32, disp: i64) void = {
	emitrex(a, rhi(srcreg), rhi(base), 1);
	emitbyte(a, opcode);
	emitmodrmmem(a, rcode(srcreg), base, disp);
};

// mem(base, disp) → reg (e.g. MOVQ mem into reg; opcode = 0x8B).
fn encodemr(a: *asm_, opcode: u8, dstreg: i32, base: i32, disp: i64) void = {
	emitrex(a, rhi(dstreg), rhi(base), 1);
	emitbyte(a, opcode);
	emitmodrmmem(a, rcode(dstreg), base, disp);
};

// OPCODE /n imm32 reg form (e.g. ADDQ $imm, reg).
fn encoderiimm32(a: *asm_, opcode: u8, subop: i32, dst: i32, imm: i32) void = {
	emitrex(a, 0, rhi(dst), 1);
	emitbyte(a, opcode);
	emitbyte(a, modrmbyte(3, subop, rcode(dst)));
	emitu32(a, imm: u32);
};

// Unary on reg: F7 /n reg, etc.
fn encodeunary(a: *asm_, opcode: u8, subop: i32, dst: i32) void = {
	emitrex(a, 0, rhi(dst), 1);
	emitbyte(a, opcode);
	emitbyte(a, modrmbyte(3, subop, rcode(dst)));
};

// SSE2 helpers. Plan 9 syntax: source first, destination second.
// For ADDSD-style ops we put dst in the reg field, src in r/m.
fn sserr(a: *asm_, prefix: u8, op2: u8, regop: i32, rmop: i32) void = {
	if (prefix != 0u8) { emitbyte(a, prefix); };
	emitrex(a, rhi(regop), rhi(rmop), 0);
	emitbyte(a, 15u8);	// 0x0F
	emitbyte(a, op2);
	emitbyte(a, modrmbyte(3, rcode(regop), rcode(rmop)));
};

fn ssemrload(a: *asm_, prefix: u8, op2: u8, regop: i32, base: i32, disp: i64) void = {
	if (prefix != 0u8) { emitbyte(a, prefix); };
	emitrex(a, rhi(regop), rhi(base), 0);
	emitbyte(a, 15u8);
	emitbyte(a, op2);
	emitmodrmmem(a, rcode(regop), base, disp);
};

// REX.W variant of sse_rr (CVTTSD2SI / CVTSI2SD).
fn sserrw(a: *asm_, prefix: u8, op2: u8, regop: i32, rmop: i32) void = {
	if (prefix != 0u8) { emitbyte(a, prefix); };
	emitrex(a, rhi(regop), rhi(rmop), 1);
	emitbyte(a, 15u8);
	emitbyte(a, op2);
	emitbyte(a, modrmbyte(3, rcode(regop), rcode(rmop)));
};

fn resolvelabel(a: *asm_, name: str) u64 = {
	let s: *asym = a.syms;
	for (s != nil) {
		if (s.defined != 0) { if (strings.compare(s.name, name) == 0) { return s.addr; }; };
		s = s.snext;
	};
	return 0u64;
};

fn labeldefined(a: *asm_, name: str) bool = {
	let s: *asym = a.syms;
	for (s != nil) {
		if (s.defined != 0) { if (strings.compare(s.name, name) == 0) { return true; }; };
		s = s.snext;
	};
	return false;
};

fn addfixup(a: *asm_, off: u64, label: str) void = {
	let f: *afixup = alloc(afixup { off = off, label = label, fnext = a.fixups })!;
	a.fixups = f;
};

fn isgpr(t: i32) bool = {
	if (t >= D_AX) { if (t <= D_R15) { return true; }; };
	return false;
};

export fn encode(a: *asm_) i32 = {
	let p: *aprog = a.head;
	for (p != nil) {
		if (p.label.len > 0) {
			let s: *asym = intern(a, p.label);
			s.defined = 1;
			s.istext = 1;
			s.addr = a.textlen;
		};
		let op: i32 = p.as_;

		if (op == A_NOP) {
			p = p.link; continue;
		};
		if (op == A_TEXT) {
			let s: *asym = intern(a, p.to.asym);
			s.defined = 1;
			s.istext = 1;
			s.isglobal = 1;
			s.addr = a.textlen;
			p = p.link; continue;
		};
		if (op == A_DATA) {
			let s: *asym = intern(a, p.to.asym);
			s.defined = 1;
			s.istext = 1;
			s.isglobal = 1;
			s.addr = a.textlen;
			let i: u64 = 0u64;
			for (i < p.nbytes) { emitbyte(a, p.bytes[i]); i += 1u64; };
			p = p.link; continue;
		};
		if (op == A_DATAW) {
			// obj.ww emits the .data section conditionally on
			// datalen > 0 so .o output stays byte-identical for
			// inputs that don't use DATAW.
			let s: *asym = intern(a, p.to.asym);
			s.defined = 1;
			s.isdata = 1;
			s.isglobal = 1;
			s.addr = a.datalen;
			let i: u64 = 0u64;
			for (i < p.nbytes) { emitdatabyte(a, p.bytes[i]); i += 1u64; };
			p = p.link; continue;
		};
		if (op == A_DATAR) {
			// DATAR slot+off(SB), target(SB) — record an
			// R_X86_64_64 relocation at slot+off in .data
			// pointing at target. Slot must already be defined
			// by a prior DATAW.
			let holder: *asym = intern(a, p.from.asym);
			// #59: a DATAR slot with no prior DATAW definition must be
			// a loud error, not a silently dropped relocation (the .o
			// would ship a zero-filled pointer slot — a null pointer at
			// link/runtime). Mirrors cmd/w6a/asm.c:363 (errs++ → main
			// returns 1 before opening the output, so no .o is written).
			if (holder.defined == 0 || holder.isdata == 0) {
				let msg: str = "w6a: DATAR slot not yet defined as DATAW: ";
				os.write(2, msg.ptr, msg.len: u64);
				os.write(2, p.from.asym.ptr, p.from.asym.len: u64);
				let wm1: str = "\n";
				os.write(2, wm1.ptr, wm1.len: u64);
				a.errs += 1;
				p = p.link; continue;
			};
			let target: *asym = intern(a, p.to.asym);
			let reloff: u64 = holder.addr + p.from.offset: u64;
			addrelocdata(a, reloff, 1 /* R_X86_64_64 */,
			    target, 0i64);
			p = p.link; continue;
		};
		if (op == A_RET) {
			emitbyte(a, 195u8);	// 0xC3
			p = p.link; continue;
		};
		if (op == A_SYSCALL) {
			emitbyte(a, 15u8);
			emitbyte(a, 5u8);
			p = p.link; continue;
		};
		if (op == A_PUSHQ) {
			if (rhi(p.to.atype) != 0) { emitbyte(a, 65u8); };	// 0x41
			emitbyte(a, (80 + rcode(p.to.atype)): u8);	// 0x50
			p = p.link; continue;
		};
		if (op == A_POPQ) {
			if (rhi(p.to.atype) != 0) { emitbyte(a, 65u8); };
			emitbyte(a, (88 + rcode(p.to.atype)): u8);	// 0x58
			p = p.link; continue;
		};
		if (op == A_NEGQ)  { encodeunary(a, 247u8, 3, p.to.atype); p = p.link; continue; };
		if (op == A_NOTQ)  { encodeunary(a, 247u8, 2, p.to.atype); p = p.link; continue; };
		if (op == A_IDIVQ) { encodeunary(a, 247u8, 7, p.to.atype); p = p.link; continue; };
		if (op == A_DIVQ)  { encodeunary(a, 247u8, 6, p.to.atype); p = p.link; continue; };
		if (op == A_CQO) {
			emitbyte(a, 72u8);	// REX.W (0x48)
			emitbyte(a, 153u8);	// 0x99
			p = p.link; continue;
		};

		if (op == A_MOVQ) {
			let ft: i32 = p.from.atype;
			let tt: i32 = p.to.atype;
			if (ft == D_CONST) { if (isgpr(tt)) {
				let v: i64 = p.from.offset;
				if (v >= -2147483648i64) { if (v <= 2147483647i64) {
					encoderiimm32(a, 199u8, 0, tt, v: i32);
					p = p.link; continue;
				};};
				// movabs r64, imm64: REX.W B8+rd imm64
				emitrex(a, 0, rhi(tt), 1);
				emitbyte(a, (184 + rcode(tt)): u8);
				let k: i32 = 0;
				for (k < 8) {
					emitbyte(a, ((v: u64 >> (k: u64 * 8u64)) & 255u64): u8);
					k += 1;
				};
				p = p.link; continue;
			};};
			if (isgpr(ft)) { if (isgpr(tt)) {
				encoderr(a, 137u8, ft, tt);	// 0x89
				p = p.link; continue;
			};};
			if (ft == D_INDIR) { if (isgpr(tt)) {
				encodemr(a, 139u8, tt, p.from.reg, p.from.offset);	// 0x8B
				p = p.link; continue;
			};};
			if (isgpr(ft)) { if (tt == D_INDIR) {
				encoderm(a, 137u8, ft, p.to.reg, p.to.offset);
				p = p.link; continue;
			};};
			if (ft == D_CONST) { if (tt == D_INDIR) {
				emitrex(a, 0, rhi(p.to.reg), 1);
				emitbyte(a, 199u8);
				emitmodrmmem(a, 0, p.to.reg, p.to.offset);
				emitu32(a, p.from.offset: u32);
				p = p.link; continue;
			};};
			if (ft == D_EXTERN) { if (isgpr(tt)) {
				// RIP-relative load: 48 8B /r mod=00 rm=5 disp32
				emitrex(a, rhi(tt), 0, 1);
				emitbyte(a, 139u8);
				emitbyte(a, modrmbyte(0, rcode(tt), 5));
				let reloff: u64 = a.textlen;
				emitu32(a, 0u32);
				let s: *asym = intern(a, p.from.asym);
				addreloc(a, reloff, 2, s, -4i64);
				p = p.link; continue;
			};};
			if (isgpr(ft)) { if (tt == D_EXTERN) {
				// RIP-relative store: 48 89 /r mod=00 rm=5 disp32
				emitrex(a, rhi(ft), 0, 1);
				emitbyte(a, 137u8);
				emitbyte(a, modrmbyte(0, rcode(ft), 5));
				let reloff: u64 = a.textlen;
				emitu32(a, 0u32);
				let s: *asym = intern(a, p.to.asym);
				addreloc(a, reloff, 2, s, -4i64);
				p = p.link; continue;
			};};
			let wm2: str = "w6a: unsupported MOVQ shape\n";
			os.write(2, wm2.ptr, wm2.len: u64);
			a.errs += 1;
			p = p.link; continue;
		};

		if (op == A_MOVB) {
			// emitrex8 forces the bare REX so SI/DI/BP/SP name
			// SIL/DIL/BPL/SPL, never AH/CH/DH/BH.
			let ft: i32 = p.from.atype;
			let tt: i32 = p.to.atype;
			if (isgpr(ft)) { if (tt == D_INDIR) {
				emitrex8(a, rhi(ft), rhi(p.to.reg), ft);
				emitbyte(a, 136u8);	// 0x88
				emitmodrmmem(a, rcode(ft), p.to.reg, p.to.offset);
				p = p.link; continue;
			};};
			if (ft == D_INDIR) { if (isgpr(tt)) {
				emitrex8(a, rhi(tt), rhi(p.from.reg), tt);
				emitbyte(a, 138u8);	// 0x8A
				emitmodrmmem(a, rcode(tt), p.from.reg, p.from.offset);
				p = p.link; continue;
			};};
			let wm3: str = "w6a: unsupported MOVB shape\n";
			os.write(2, wm3.ptr, wm3.len: u64);
			a.errs += 1;
			p = p.link; continue;
		};

		if (op == A_MOVW) {
			// 16-bit MOV: 0x66 operand-size prefix + the 32-bit
			// MOV opcodes 0x89 / 0x8B. No REX.W.
			let ft: i32 = p.from.atype;
			let tt: i32 = p.to.atype;
			if (isgpr(ft)) { if (tt == D_INDIR) {
				emitbyte(a, 102u8);	// 0x66
				emitrex(a, rhi(ft), rhi(p.to.reg), 0);
				emitbyte(a, 137u8);	// 0x89
				emitmodrmmem(a, rcode(ft), p.to.reg, p.to.offset);
				p = p.link; continue;
			};};
			if (ft == D_INDIR) { if (isgpr(tt)) {
				emitbyte(a, 102u8);	// 0x66
				emitrex(a, rhi(tt), rhi(p.from.reg), 0);
				emitbyte(a, 139u8);	// 0x8B
				emitmodrmmem(a, rcode(tt), p.from.reg, p.from.offset);
				p = p.link; continue;
			};};
			let wm4: str = "w6a: unsupported MOVW shape\n";
			os.write(2, wm4.ptr, wm4.len: u64);
			a.errs += 1;
			p = p.link; continue;
		};

		if (op == A_MOVZWQ) {
			// MOVZX r64, r/m16 — 0F B7 /r with REX.W.
			let ft: i32 = p.from.atype;
			let tt: i32 = p.to.atype;
			if (ft == D_INDIR) { if (isgpr(tt)) {
				emitrex(a, rhi(tt), rhi(p.from.reg), 1);
				emitbyte(a, 15u8);
				emitbyte(a, 183u8);	// 0xB7
				emitmodrmmem(a, rcode(tt), p.from.reg, p.from.offset);
				p = p.link; continue;
			};};
			let wm5: str = "w6a: unsupported MOVZWQ shape\n";
			os.write(2, wm5.ptr, wm5.len: u64);
			a.errs += 1;
			p = p.link; continue;
		};

		if (op == A_MOVSWQ) {
			// MOVSX r64, r/m16 — 0F BF /r with REX.W.
			let ft: i32 = p.from.atype;
			let tt: i32 = p.to.atype;
			if (ft == D_INDIR) { if (isgpr(tt)) {
				emitrex(a, rhi(tt), rhi(p.from.reg), 1);
				emitbyte(a, 15u8);
				emitbyte(a, 191u8);	// 0xBF
				emitmodrmmem(a, rcode(tt), p.from.reg, p.from.offset);
				p = p.link; continue;
			};};
			if (isgpr(ft)) { if (isgpr(tt)) {
				emitrex(a, rhi(tt), rhi(ft), 1);
				emitbyte(a, 15u8);
				emitbyte(a, 191u8);	// 0xBF
				emitbyte(a, modrmbyte(3, rcode(tt), rcode(ft)));
				p = p.link; continue;
			};};
			let wm6: str = "w6a: unsupported MOVSWQ shape\n";
			os.write(2, wm6.ptr, wm6.len: u64);
			a.errs += 1;
			p = p.link; continue;
		};

		if (op == A_MOVSBQ) {
			// MOVSX r64, r/m8 — 0F BE /r with REX.W.
			let ft: i32 = p.from.atype;
			let tt: i32 = p.to.atype;
			if (ft == D_INDIR) { if (isgpr(tt)) {
				emitrex(a, rhi(tt), rhi(p.from.reg), 1);
				emitbyte(a, 15u8);
				emitbyte(a, 190u8);	// 0xBE
				emitmodrmmem(a, rcode(tt), p.from.reg, p.from.offset);
				p = p.link; continue;
			};};
			if (isgpr(ft)) { if (isgpr(tt)) {
				emitrex(a, rhi(tt), rhi(ft), 1);
				emitbyte(a, 15u8);
				emitbyte(a, 190u8);	// 0xBE
				emitbyte(a, modrmbyte(3, rcode(tt), rcode(ft)));
				p = p.link; continue;
			};};
			let wm7: str = "w6a: unsupported MOVSBQ shape\n";
			os.write(2, wm7.ptr, wm7.len: u64);
			a.errs += 1;
			p = p.link; continue;
		};

		if (op == A_MOVZBQ) {
			let ft: i32 = p.from.atype;
			let tt: i32 = p.to.atype;
			if (ft == D_INDIR) { if (isgpr(tt)) {
				emitrex(a, rhi(tt), rhi(p.from.reg), 1);
				emitbyte(a, 15u8);
				emitbyte(a, 182u8);	// 0xB6
				emitmodrmmem(a, rcode(tt), p.from.reg, p.from.offset);
				p = p.link; continue;
			};};
			let wm8: str = "w6a: unsupported MOVZBQ shape\n";
			os.write(2, wm8.ptr, wm8.len: u64);
			a.errs += 1;
			p = p.link; continue;
		};

		if (op == A_MOVL) {
			let ft: i32 = p.from.atype;
			let tt: i32 = p.to.atype;
			if (isgpr(ft)) { if (tt == D_INDIR) {
				emitrex(a, rhi(ft), rhi(p.to.reg), 0);
				emitbyte(a, 137u8);
				emitmodrmmem(a, rcode(ft), p.to.reg, p.to.offset);
				p = p.link; continue;
			};};
			if (ft == D_INDIR) { if (isgpr(tt)) {
				emitrex(a, rhi(tt), rhi(p.from.reg), 0);
				emitbyte(a, 139u8);
				emitmodrmmem(a, rcode(tt), p.from.reg, p.from.offset);
				p = p.link; continue;
			};};
			if (isgpr(ft)) { if (isgpr(tt)) {
				emitrex(a, rhi(ft), rhi(tt), 0);
				emitbyte(a, 137u8);
				emitbyte(a, modrmbyte(3, rcode(ft), rcode(tt)));
				p = p.link; continue;
			};};
			let wm9: str = "w6a: unsupported MOVL shape\n";
			os.write(2, wm9.ptr, wm9.len: u64);
			a.errs += 1;
			p = p.link; continue;
		};

		if (op == A_MOVSXD) {
			let ft: i32 = p.from.atype;
			let tt: i32 = p.to.atype;
			if (ft == D_INDIR) { if (isgpr(tt)) {
				emitrex(a, rhi(tt), rhi(p.from.reg), 1);
				emitbyte(a, 99u8);	// 0x63
				emitmodrmmem(a, rcode(tt), p.from.reg, p.from.offset);
				p = p.link; continue;
			};};
			if (isgpr(ft)) { if (isgpr(tt)) {
				emitrex(a, rhi(tt), rhi(ft), 1);
				emitbyte(a, 99u8);	// 0x63
				emitbyte(a, modrmbyte(3, rcode(tt), rcode(ft)));
				p = p.link; continue;
			};};
			let wm10: str = "w6a: unsupported MOVSXD shape\n";
			os.write(2, wm10.ptr, wm10.len: u64);
			a.errs += 1;
			p = p.link; continue;
		};

		if (op == A_MOVSD) {
			let ft: i32 = p.from.atype;
			let tt: i32 = p.to.atype;
			if (isxmm(ft)) { if (isxmm(tt)) {
				sserr(a, 242u8, 16u8, tt, ft);
				p = p.link; continue;
			};};
			if (ft == D_INDIR) { if (isxmm(tt)) {
				ssemrload(a, 242u8, 16u8, tt, p.from.reg, p.from.offset);
				p = p.link; continue;
			};};
			if (isxmm(ft)) { if (tt == D_INDIR) {
				ssemrload(a, 242u8, 17u8, ft, p.to.reg, p.to.offset);
				p = p.link; continue;
			};};
			let wm11: str = "w6a: unsupported MOVSD shape\n";
			os.write(2, wm11.ptr, wm11.len: u64);
			a.errs += 1;
			p = p.link; continue;
		};

		if (op == A_ADDSD) { sserr(a, 242u8, 88u8,  p.to.atype, p.from.atype); p = p.link; continue; };
		if (op == A_SUBSD) { sserr(a, 242u8, 92u8,  p.to.atype, p.from.atype); p = p.link; continue; };
		if (op == A_MULSD) { sserr(a, 242u8, 89u8,  p.to.atype, p.from.atype); p = p.link; continue; };
		if (op == A_DIVSD) { sserr(a, 242u8, 94u8,  p.to.atype, p.from.atype); p = p.link; continue; };
		if (op == A_UCOMISD)   { sserr(a, 102u8, 46u8, p.to.atype, p.from.atype); p = p.link; continue; };
		if (op == A_CVTTSD2SI) { sserrw(a, 242u8, 44u8, p.to.atype, p.from.atype); p = p.link; continue; };
		if (op == A_CVTSI2SD)  { sserrw(a, 242u8, 42u8, p.to.atype, p.from.atype); p = p.link; continue; };

		if (op == A_MOVSS) {
			let ft: i32 = p.from.atype;
			let tt: i32 = p.to.atype;
			if (isxmm(ft)) { if (isxmm(tt)) {
				sserr(a, 243u8, 16u8, tt, ft); p = p.link; continue;
			};};
			if (ft == D_INDIR) { if (isxmm(tt)) {
				ssemrload(a, 243u8, 16u8, tt, p.from.reg, p.from.offset);
				p = p.link; continue;
			};};
			if (isxmm(ft)) { if (tt == D_INDIR) {
				ssemrload(a, 243u8, 17u8, ft, p.to.reg, p.to.offset);
				p = p.link; continue;
			};};
			let wm12: str = "w6a: unsupported MOVSS shape\n";
			os.write(2, wm12.ptr, wm12.len: u64);
			a.errs += 1;
			p = p.link; continue;
		};

		if (op == A_ADDSS) { sserr(a, 243u8, 88u8, p.to.atype, p.from.atype); p = p.link; continue; };
		if (op == A_SUBSS) { sserr(a, 243u8, 92u8, p.to.atype, p.from.atype); p = p.link; continue; };
		if (op == A_MULSS) { sserr(a, 243u8, 89u8, p.to.atype, p.from.atype); p = p.link; continue; };
		if (op == A_DIVSS) { sserr(a, 243u8, 94u8, p.to.atype, p.from.atype); p = p.link; continue; };
		if (op == A_UCOMISS)   { sserr(a, 0u8,   46u8, p.to.atype, p.from.atype); p = p.link; continue; };
		if (op == A_CVTTSS2SI) { sserrw(a, 243u8, 44u8, p.to.atype, p.from.atype); p = p.link; continue; };
		if (op == A_CVTSI2SS)  { sserrw(a, 243u8, 42u8, p.to.atype, p.from.atype); p = p.link; continue; };
		if (op == A_CVTSD2SS)  { sserr(a, 242u8, 90u8, p.to.atype, p.from.atype); p = p.link; continue; };
		if (op == A_CVTSS2SD)  { sserr(a, 243u8, 90u8, p.to.atype, p.from.atype); p = p.link; continue; };

		if (op == A_ADDQ) {
			let ft: i32 = p.from.atype;
			let tt: i32 = p.to.atype;
			if (ft == D_CONST) { if (isgpr(tt)) {
				encoderiimm32(a, 129u8, 0, tt, p.from.offset: i32);	// 0x81
				p = p.link; continue;
			};};
			if (ft == D_CONST) { if (tt == D_INDIR) {
				emitrex(a, 0, rhi(p.to.reg), 1);
				emitbyte(a, 129u8);
				emitmodrmmem(a, 0, p.to.reg, p.to.offset);
				emitu32(a, p.from.offset: u32);
				p = p.link; continue;
			};};
			if (isgpr(ft)) { if (tt == D_INDIR) {
				encoderm(a, 1u8, ft, p.to.reg, p.to.offset);
				p = p.link; continue;
			};};
			if (ft == D_INDIR) { if (isgpr(tt)) {
				encodemr(a, 3u8, tt, p.from.reg, p.from.offset);
				p = p.link; continue;
			};};
			encoderr(a, 1u8, ft, tt);
			p = p.link; continue;
		};

		if (op == A_SUBQ) {
			let ft: i32 = p.from.atype;
			let tt: i32 = p.to.atype;
			if (ft == D_CONST) { if (isgpr(tt)) {
				encoderiimm32(a, 129u8, 5, tt, p.from.offset: i32);
				p = p.link; continue;
			};};
			if (ft == D_CONST) { if (tt == D_INDIR) {
				emitrex(a, 0, rhi(p.to.reg), 1);
				emitbyte(a, 129u8);
				emitmodrmmem(a, 5, p.to.reg, p.to.offset);
				emitu32(a, p.from.offset: u32);
				p = p.link; continue;
			};};
			if (isgpr(ft)) { if (tt == D_INDIR) {
				encoderm(a, 41u8, ft, p.to.reg, p.to.offset);	// 0x29
				p = p.link; continue;
			};};
			if (ft == D_INDIR) { if (isgpr(tt)) {
				encodemr(a, 43u8, tt, p.from.reg, p.from.offset);	// 0x2B
				p = p.link; continue;
			};};
			encoderr(a, 41u8, ft, tt);
			p = p.link; continue;
		};

		if (op == A_ANDQ) {
			// AND r/m64, imm32 — 0x81 /4 (REX.W). Without the
			// D_CONST path encoderr would silently emit 0x21
			// with garbage reg fields.
			let ft: i32 = p.from.atype;
			let tt: i32 = p.to.atype;
			if (ft == D_CONST) { if (isgpr(tt)) {
				encoderiimm32(a, 129u8, 4, tt, p.from.offset: i32);
				p = p.link; continue;
			};};
			encoderr(a, 33u8, ft, tt);	// 0x21
			p = p.link; continue;
		};
		if (op == A_ORQ) {
			// OR r/m64, imm32 — 0x81 /1 (REX.W). Mirrors ANDQ.
			let ft: i32 = p.from.atype;
			let tt: i32 = p.to.atype;
			if (ft == D_CONST) { if (isgpr(tt)) {
				encoderiimm32(a, 129u8, 1, tt, p.from.offset: i32);
				p = p.link; continue;
			};};
			encoderr(a, 9u8, ft, tt);	// 0x09
			p = p.link; continue;
		};
		if (op == A_XORQ) {
			let ft: i32 = p.from.atype;
			let tt: i32 = p.to.atype;
			if (ft == D_CONST) { if (isgpr(tt)) {
				encoderiimm32(a, 129u8, 6, tt, p.from.offset: i32);
				p = p.link; continue;
			};};
			encoderr(a, 49u8, ft, tt);	// 0x31
			p = p.link; continue;
		};
		if (op == A_IMULQ) {
			emitrex(a, rhi(p.to.atype), rhi(p.from.atype), 1);
			emitbyte(a, 15u8);
			emitbyte(a, 175u8);	// 0xAF
			emitbyte(a, modrmbyte(3, rcode(p.to.atype), rcode(p.from.atype)));
			p = p.link; continue;
		};
		if (op == A_SHLQ) { encodeunary(a, 211u8, 4, p.to.atype); p = p.link; continue; };	// 0xD3
		if (op == A_SHRQ) { encodeunary(a, 211u8, 5, p.to.atype); p = p.link; continue; };
		// #136: SAR r/m64, CL — REX.W + D3 /7 (arithmetic right
		// shift, sign-extends MSB; cstage twin cmd/w6a/asm.c).
		if (op == A_SARQ) { encodeunary(a, 211u8, 7, p.to.atype); p = p.link; continue; };
		if (op == A_CMPQ) {
			let ft: i32 = p.from.atype;
			let tt: i32 = p.to.atype;
			if (ft == D_CONST) { if (isgpr(tt)) {
				encoderiimm32(a, 129u8, 7, tt, p.from.offset: i32);
				p = p.link; continue;
			};};
			encoderr(a, 57u8, ft, tt);	// 0x39
			p = p.link; continue;
		};

		if (op == A_LEAQ) {
			let ft: i32 = p.from.atype;
			let tt: i32 = p.to.atype;
			if (ft == D_INDIR) { if (isgpr(tt)) {
				encodemr(a, 141u8, tt, p.from.reg, p.from.offset);	// 0x8D
				p = p.link; continue;
			};};
			if (ft == D_EXTERN) { if (isgpr(tt)) {
				emitrex(a, rhi(tt), 0, 1);
				emitbyte(a, 141u8);
				emitbyte(a, modrmbyte(0, rcode(tt), 5));
				let reloff: u64 = a.textlen;
				emitu32(a, 0u32);
				let s: *asym = intern(a, p.from.asym);
				addreloc(a, reloff, 2, s, -4i64);
				p = p.link; continue;
			};};
			let wml: str = "w6a: unsupported LEAQ shape\n";
			os.write(2, wml.ptr, wml.len: u64);
			a.errs += 1;
			p = p.link; continue;
		};

		if (op == A_CALL) {
			let tt: i32 = p.to.atype;
			if (tt == D_EXTERN) {
				emitbyte(a, 232u8);	// 0xE8
				let reloff: u64 = a.textlen;
				emitu32(a, 0u32);
				let s: *asym = intern(a, p.to.asym);
				addreloc(a, reloff, 4, s, -4i64);
				p = p.link; continue;
			};
			if (tt == D_BRANCH) {
				emitbyte(a, 232u8);
				addfixup(a, a.textlen, p.to.asym);
				emitu32(a, 0u32);
				p = p.link; continue;
			};
			if (isgpr(tt)) {
				if (rhi(tt) != 0) { emitbyte(a, 65u8); };
				emitbyte(a, 255u8);	// 0xFF
				emitbyte(a, modrmbyte(3, 2, rcode(tt)));
				p = p.link; continue;
			};
			let wmc: str = "w6a: unsupported CALL shape\n";
			os.write(2, wmc.ptr, wmc.len: u64);
			a.errs += 1;
			p = p.link; continue;
		};

		if (op == A_JMP) {
			emitbyte(a, 233u8);	// 0xE9
			addfixup(a, a.textlen, p.to.asym);
			emitu32(a, 0u32);
			p = p.link; continue;
		};

		// Conditional jumps. 0x0F + cc + rel32.
		let cc: u8 = 0u8;
		let isjcc: bool = true;
		switch (op) {
		case A_JE:  cc = 132u8;	// 0x84
		case A_JZ:  cc = 132u8;
		case A_JNE: cc = 133u8;
		case A_JNZ: cc = 133u8;
		case A_JL:  cc = 140u8;
		case A_JLE: cc = 142u8;
		case A_JG:  cc = 143u8;
		case A_JGE: cc = 141u8;
		case A_JB:  cc = 130u8;
		case A_JBE: cc = 134u8;
		case A_JA:  cc = 135u8;
		case A_JAE: cc = 131u8;
		case A_JP:  cc = 138u8;	// 0x8A, UCOMISD unordered (#97)
		case:       isjcc = false;
		};
		if (isjcc) {
			emitbyte(a, 15u8);
			emitbyte(a, cc);
			addfixup(a, a.textlen, p.to.asym);
			emitu32(a, 0u32);
			p = p.link; continue;
		};

		let wm13: str = "w6a: unsupported opcode\n";
		os.write(2, wm13.ptr, wm13.len: u64);
		a.errs += 1;
		p = p.link;
	};

	// Second pass: patch fixups (forward label refs).
	let f: *afixup = a.fixups;
	for (f != nil) {
		if (!labeldefined(a, f.label)) {
			let wm14: str = "w6a: undefined label '";
			os.write(2, wm14.ptr, wm14.len: u64);
			let lbl: str = f.label;
			os.write(2, lbl.ptr, lbl.len: u64);
			let wm15: str = "'\n";
			os.write(2, wm15.ptr, wm15.len: u64);
			a.errs += 1;
			f = f.fnext;
			continue;
		};
		let target: u64 = resolvelabel(a, f.label);
		let rel: i64 = target: i64 - (f.off: i64 + 4i64);
		let rel32: u32 = rel: u32;
		a.text[f.off]         = (rel32 & 255u32): u8;
		a.text[f.off + 1u64]  = ((rel32 >> 8u32)  & 255u32): u8;
		a.text[f.off + 2u64]  = ((rel32 >> 16u32) & 255u32): u8;
		a.text[f.off + 3u64]  = ((rel32 >> 24u32) & 255u32): u8;
		f = f.fnext;
	};
	return a.errs;
};