ww/selfhost/cmd/wcc/cgen.ww

// selfhost/cmd/wcc/cgen.ww — port of cmd/w6c/cgen.c.
//
// Status: GROWING. Each subsystem we add is verified by `wwdump_ww -c`
// producing byte-identical output to C-side `w6c` for the same source,
// then by assembling + linking + running the result.
//
// Current coverage:
//   - decls:  nkind.N_FILE, nkind.N_FNDECL (params, frame for locals, prologue
//             + dual-epilogue suppression; FFI body-less fn skipped)
//   - stmts:  nkind.N_BLOCK, nkind.N_RETURN, nkind.N_EXPRSTMT, nkind.N_LET (no init),
//             nkind.N_LET (int-literal / ident / call / nkind.N_BIN init),
//             nkind.N_IF (with optional else), nkind.N_FOR (cond-only and full
//             init/cond/post), nkind.N_BREAK, nkind.N_CONTINUE
//   - exprs:  nkind.N_INTLIT, nkind.N_IDENT (local/param), nkind.N_BIN with full op
//             coverage (+/-/*/// %, &/|/^, <</>>, comparisons with
//             signed-vs-unsigned dispatch, &&/||), nkind.N_UN (- ! ~ &amp; *),
//             nkind.N_CALL (recursive R-to-L push, pop into argregs L-to-R),
//             nkind.N_ASSIGN to local idents (plain and compound +=/-=)
//
// Type info is shallow — frame slots are 8 bytes per local, all loads
// /stores are MOVQ. Programs that mix i8/i32/i64 locals work but spill
// 8 bytes per local. Float, str, slice, struct, match, defer, alloc,
// tagged-union return — none of those are wired yet.

use os;
use mem;
use ast;
use tok;
use typ;
use sym;
use strconv;
// Split files. Bundler pulls these in transitively so consumers only
// need `use cgen;`. Order matters for the flat-bundle concat — utils
// first so cgenexpr/stmt/decl can reference helpers defined here.
use cgenutil;
use cgenexpr;
use cgenstmt;
use cgendecl;

// ---- typedef alias registry -----------------------------------------
//
// `type error = str;` makes `error` a struct-shape alias. We track
// alias→target so isstrtype / isslicetype / structlookup can
// resolve through the chain. Only direct nkind.N_TNAME aliases are mapped;
// `type p = struct {...}` is handled by collectstructs.

type aliasent = struct {
	aname:   str,
	amod:    str,	// originating module (`// MODULE: foo`), or empty
	target:  *node,	// the rhs type expr
	aanext:  *aliasent,
};

fn collectaliases(c: *cgen, file: *node) void = {
	c.aliases = nil;
	let d: *node = file.list;
	for (d != nil) {
		if (d.kind == nkind.N_TYPEDECL) {
			let body: *node = d.lhs;
			if (body != nil) {
				if (body.kind != nkind.N_TSTRUCT) {
					let a: *aliasent = amalloc(c.a, 64u64): *aliasent;
					a.aname = d.str;
					a.amod = d.module;
					a.target = body;
					a.aanext = c.aliases;
					c.aliases = a;
				};
			};
		};
		d = d.next;
	};
};

fn aliaslookup(c: *cgen, name: str) *node = {
	// Same-module first, then any. Mirrors cstage's scope_lookup_prefer
	// (cmd/wcc/check.c:65); without the prefer pass a bare `invalid`
	// in module M with `type invalid = !void;` can collapse onto a
	// strconv-style `type invalid = !i32;` registered earlier in
	// c.aliases (head-first walk). The leaf-collision then drives a
	// narrow MOVSXD load of a slot the let-decl zero-inits 8B-wide
	// (task #27 silent-correct-by-zero-init).
	let a: *aliasent = c.aliases;
	for (a != nil) {
		if (streq(a.aname, name)) {
			if (streq(a.amod, c.curmod)) { return a.target; };
		};
		a = a.aanext;
	};
	a = c.aliases;
	for (a != nil) {
		if (streq(a.aname, name)) { return a.target; };
		a = a.aanext;
	};
	// Module-qualified form: `pkg.alias` → match the leaf name
	// scoped to its originating module. Mirrors check.c's module-
	// qualified type resolution; requiring `amod == pkg` is what
	// prevents two modules with same-leaf-name aliases from
	// collapsing into whichever entry appears first in the chain.
	let i: i32 = name.len - 1;
	for (i >= 0) {
		if (name[i] == 46u8) { // '.'
			let pkg: str;
			pkg.ptr = name.ptr;
			pkg.len = i;
			let leaf: str;
			leaf.ptr = name.ptr + ((i + 1): u64);
			leaf.len = name.len - (i + 1);
			let b: *aliasent = c.aliases;
			for (b != nil) {
				if (streq(b.aname, leaf)) {
					if (streq(b.amod, pkg)) {
						return b.target;
					};
				};
				b = b.aanext;
			};
			i = -1;
		} else {
			i -= 1;
		};
	};
	return nil;
};

// ---- enum registry --------------------------------------------------
//
// Mirrors cmd/wcc/check.c's enum resolution at collect time: walk
// every `type Foo = enum [storage] { ... }`, pre-compute each
// member's u64 value (supporting auto-increment and sibling refs),
// and stash them so cgdot can fold `Foo.MEMBER` → MOVQ $value, AX.

// foldintliteral — fold the literal subset usable for top-level
// constant slots: int/rune literal, true/false/nil, and a unary
// +/-/~ over the same (any depth). No sibling-ident, no binary op.
// Shared between enumevalmember (literal leaves) and
// emitdefconstants (top-level def rhs).
//
// Whitelist kept tight on purpose: anything richer (sibling refs,
// arithmetic) belongs in enumevalmember, which calls this for its
// literal leaves and handles the rest itself.
fn foldintliteral(e: *node, out: *u64) bool = {
	if (e == nil) { return false; };
	let k: nkind = e.kind;
	if (k == nkind.N_INTLIT)  { *out = e.uval; return true; };
	if (k == nkind.N_RUNELIT) { *out = e.uval; return true; };
	if (k == nkind.N_TRUE)    { *out = 1u64; return true; };
	if (k == nkind.N_FALSE)   { *out = 0u64; return true; };
	if (k == nkind.N_NIL)     { *out = 0u64; return true; };
	if (k == nkind.N_UN) {
		let v: u64;
		if (!foldintliteral(e.lhs, &v)) { return false; };
		let op: tkind = e.op;
		if (op == tkind.TK_MINUS) { *out = (-(v: i64)): u64; return true; };
		if (op == tkind.TK_TILDE) { *out = ~v; return true; };
		if (op == tkind.TK_PLUS)  { *out = v; return true; };
		return false;
	};
	return false;
};

fn enumevalmember(prev: *enummember, e: *node, out: *u64) bool = {
	if (e == nil) { return false; };
	if (foldintliteral(e, out)) { return true; };
	let k: nkind = e.kind;
	if (k == nkind.N_IDENT) {
		let m: *enummember = prev;
		for (m != nil) {
			if (streq(m.mname, e.str)) {
				*out = m.mval;
				return true;
			};
			m = m.emnext;
		};
		return false;
	};
	if (k == nkind.N_BIN) {
		let a: u64;
		let b: u64;
		if (!enumevalmember(prev, e.lhs, &a)) { return false; };
		if (!enumevalmember(prev, e.rhs, &b)) { return false; };
		let op: tkind = e.op;
		if (op == tkind.TK_PLUS)    { *out = a + b; return true; };
		if (op == tkind.TK_MINUS)   { *out = a - b; return true; };
		if (op == tkind.TK_STAR)    { *out = a * b; return true; };
		if (op == tkind.TK_SLASH) {
			if (b == 0u64) { return false; };
			*out = a / b; return true;
		};
		if (op == tkind.TK_PERCENT) {
			if (b == 0u64) { return false; };
			*out = a % b; return true;
		};
		if (op == tkind.TK_AMP)     { *out = a & b; return true; };
		if (op == tkind.TK_PIPE)    { *out = a | b; return true; };
		if (op == tkind.TK_CARET)   { *out = a ^ b; return true; };
		if (op == tkind.TK_LSHIFT)  { *out = a << b; return true; };
		if (op == tkind.TK_RSHIFT)  { *out = a >> b; return true; };
		return false;
	};
	if (k == nkind.N_UN) {
		let v: u64;
		if (!enumevalmember(prev, e.lhs, &v)) { return false; };
		let op: tkind = e.op;
		if (op == tkind.TK_MINUS) { *out = (-(v: i64)): u64; return true; };
		if (op == tkind.TK_TILDE) { *out = ~v; return true; };
		if (op == tkind.TK_PLUS)  { *out = v; return true; };
		return false;
	};
	return false;
};

fn collectenums(c: *cgen, file: *node) void = {
	c.enums = nil;
	let d: *node = file.list;
	for (d != nil) {
		if (d.kind == nkind.N_TYPEDECL) {
			let body: *node = d.lhs;
			if (body != nil) {
				if (body.kind == nkind.N_TENUM) {
					let et: *enumtype = amalloc(c.a, 64u64): *enumtype;
					et.ename = d.str;
					et.emod = d.module;
					et.storage = body.lhs;
					et.members = nil;
					let prev: u64 = (-1i64): u64;
					let mhead: *enummember = nil;
					let mtail: *enummember = nil;
					let m: *node = body.list;
					for (m != nil) {
						let val: u64;
						if (m.lhs == nil) {
							val = prev + 1u64;
						} else {
							if (!enumevalmember(mhead, m.lhs, &val)) {
								val = prev + 1u64;
							};
						};
						prev = val;
						let em: *enummember = amalloc(c.a, 32u64): *enummember;
						em.mname = m.str;
						em.mval = val;
						em.emnext = nil;
						if (mhead == nil) { mhead = em; mtail = em; }
						else { mtail.emnext = em; mtail = em; };
						m = m.next;
					};
					et.members = mhead;
					et.etnext = c.enums;
					c.enums = et;
				};
			};
		};
		d = d.next;
	};
};

fn enumlookup(c: *cgen, name: str) *enumtype = {
	// Exact match first: bare-from-source idents and already-leafed
	// names hit here directly.
	let e: *enumtype = c.enums;
	for (e != nil) {
		if (streq(e.ename, name)) { return e; };
		e = e.etnext;
	};
	// Module-qualified form: `pkg.enum` → match the leaf scoped to
	// its originating module. Mirrors aliaslookup's mod-filter; the
	// `emod == pkg` guard is what prevents two modules with same-
	// leaf-name enums from collapsing into whichever entry appears
	// first in the chain.
	let i: i32 = name.len - 1;
	for (i >= 0) {
		if (name[i] == 46u8) {	// '.'
			let pkg: str;
			pkg.ptr = name.ptr;
			pkg.len = i;
			let leaf: str;
			leaf.ptr = name.ptr + ((i + 1): u64);
			leaf.len = name.len - (i + 1);
			let b: *enumtype = c.enums;
			for (b != nil) {
				if (streq(b.ename, leaf)) {
					if (streq(b.emod, pkg)) {
						return b;
					};
				};
				b = b.etnext;
			};
			return nil;
		};
		i -= 1;
	};
	return nil;
};

fn enummemberval(en: *enumtype, mname: str, out: *u64) bool = {
	let m: *enummember = en.members;
	for (m != nil) {
		if (streq(m.mname, mname)) {
			*out = m.mval;
			return true;
		};
		m = m.emnext;
	};
	return false;
};

// resolvetype — follow typedef alias chains to a "canonical" type
// expr (str/slice/array/struct/...). Stops on cycles via depth limit.
fn resolvetype(c: *cgen, t: *node) *node = {
	let cur: *node = t;
	let depth: i32 = 0;
	for (depth < 16) {
		if (cur == nil) { return nil; };
		if (cur.kind != nkind.N_TNAME) { return cur; };
		let nm: str = cur.str;
		let next: *node = aliaslookup(c, nm);
		if (next == nil) { return cur; };
		cur = next;
		depth += 1;
	};
	return cur;
};

// ---- struct registry ------------------------------------------------
//
// Per-file map from struct name → list of fields with computed offsets
// and sizes. Built when cgfile walks nkind.N_TYPEDECL with nkind.N_TSTRUCT lhs.
// nkind.N_DOT and nkind.N_ASSIGN consult this to resolve `s.field` for struct or
// *struct bases.

type fieldinfo = struct {
	fname: str,
	foff:  i32,
	fsz:   i32,
	tnode: *node,	// the field type expr, for nested struct lookups
	finext: *fieldinfo,
};

type structinfo = struct {
	sname:    str,
	smod:     str,	// originating module (`// MODULE: foo`), or empty
	fields:   *fieldinfo,
	totsize: i32,
	sinext:   *structinfo,
};

// ---- locals / frame --------------------------------------------------

type local = struct {
	name:  str,
	off:   i32,
	tnode: *node,	// declared type expr (nkind.N_TNAME / nkind.N_TPTR / ...) or nil
	lnext: *local,
};

// strlit — interned string literal record. Emitted as a DATA directive
// after all functions; cgexpr nkind.N_STRLIT loads (LEAQ ptr, MOVQ len).
type strlit = struct {
	label: str,	// "_S_<seq>"
	bytes: str,
	slnext: *strlit,
};

// ffi — `@symbol("name")` mapping. Body-less fn `foo` with this attr
// gets its CALL target rewritten to `name`.
type ffi = struct {
	ident:  str,
	symbol: str,
	fnext:  *ffi,
};

// enummember — one (name, value) pair belonging to a registered enum.
// Values are pre-computed at collect time (Hare allows sibling refs
// like `RDWR = READ | WRITE`, so we walk the value expr against the
// already-resolved siblings). Lookup is linear; enum cardinality is
// usually small.
type enummember = struct {
	mname:  str,
	mval:   u64,
	emnext: *enummember,
};

type enumtype = struct {
	ename:   str,
	emod:    str,	// originating module (`// MODULE: foo`), or empty
	storage: *node,	// AST type expr for the storage type (i32 by default)
	members: *enummember,
	etnext:  *enumtype,
};

def LOOP_MAX: i32 = 16;
def DEFER_MAX: i32 = 16;

type cgen = struct {
	a:        *arena,
	locals:   *local,
	frame:    i32,
	lastwasreturn: i32,
	labelseq: i32,
	strlitseq: i32,
	strlits: *strlit,
	ffis:    *ffi,
	defs:    *defent,
	fnrets:  *fnret,
	aliases: *aliasent,
	structs: *structinfo,
	enums:   *enumtype,
	mods:    *modent,	// fn (any export status) + non-exported
				// let/def/type decls → originating module
	lets:    *letvar,	// top-level mutable scalar `let` bindings
	fnname:  str,
	curmod:  str,		// current fn's `// MODULE: foo` directive (len=0
				// when the fn is in the primary file). Drives
				// bare-IDENT call mangling — `frob()` from
				// inside lib/foo binds to `foo.frob` even when
				// other modules also export `frob`. Set in cgfn
				// before walking the body.
	fnret:   *node,	// declared return type of current fn (or nil)
	looptop: i32,
	loopendbuf:  *str,	// stack of end labels for break
	loopcontbuf: *str,	// stack of cont labels for continue
	yieldtop: i32,
	yieldbuf:    *str,	// stack of match end labels for yield
	defertop:    i32,
	deferbuf:    **node,	// stack of deferred exprs (LIFO at return)
	// Variadic-call gather state. scanlocals walks the body in pre-
	// order DFS and assigns per-call scratch names `@vararg_d_N` /
	// `@vararg_sl_N` using this counter; cgcall resets and walks in
	// the same order so the names line up at emission time.
	varargseq: i32,
	// Max @tagscr slot_sz across all reservation sites in the current
	// function. scanlocals bumps; every emit-time `localadd("@tagscr",
	// ...)` passes this same size so the first allocation lands a slot
	// big enough for every later user. Single source of truth — pins
	// rob's "scan + emit lockstep" invariant. Reset per cgfn.
	tagscrsz: i32,
	// Live @retscr offset (#14). c.locals-based `@`-prefix dedup in
	// localadd is unwound by cgblock save/restore (post-#27), so a
	// second `return` in a sibling/outer block reallocates a fresh
	// slot — emit grew the frame past what scanlocals reserved, and
	// the stomp landed below SP. retscroff is the persistent SSoT:
	// 0 means "not yet allocated"; first emit-site sets it, every
	// later emit reuses. Mirrors c.tagscrsz pattern (#38) but tracks
	// offset, not size (per-fn return type is fixed, so size is too).
	retscroff: i32,
	// System V AMD64 sret discipline (#23). Plain TY_STRUCT returns
	// with size > 24B are passed via a hidden first-arg pointer
	// (RDI) to a caller-prealloc dest; the callee writes through
	// that pointer and returns it in RAX.
	//
	// sretargoff  — callee-side @sretarg slot (8B, holds saved RDI).
	//               Set in cgfn prologue when the fn's return type
	//               triggers sret. 0 means N/A.
	// sretdestoff — caller-side dest BP offset, propagated from a
	//               receive site (cglet / cgassign ident) to the
	//               nested cgexpr → cgcall so the call emits
	//               `LEAQ off(BP), DI` instead of allocating a
	//               scratch. 0 means no receiver wired.
	// sretscroff  — per-fn @sretscr discard slot, used by sret CALLs
	//               whose result has no named receiver. Single-slot
	//               SSoT mirroring c.retscroff; the scanlocals walk
	//               sums c.sretscrsz to pre-reserve.
	// sretscrsz   — max sret discard size in this fn (sums during
	//               scanlocals, consumed by localadd("@sretscr", ...)).
	// sretforward — set by cgreturn `return f();` from an sret callee to
	//               signal cgcall: source RDI for inner from outer's
	//               saved @sretarg (MOVQ) instead of LEAQ'ing a local
	//               dest. Inner writes into outer's caller-prealloc;
	//               inner's RAX (the dest pointer) is already outer's
	//               return value. Cleared after cgcall consumes it.
	sretargoff: i32,
	sretdestoff: i32,
	sretscroff: i32,
	sretscrsz: i32,
	sretforward: i32,
};

// Top-level mutable `let` registry. Mirrors cmd/w6c/cgen.c LetVar.
// Populated alongside modents; consulted by cgassign, cgdot, cgident
// and the TK_AMP path so reads/writes hit a RIP-relative DATAW slot
// instead of being silently dropped. tnode is the declared type AST
// node — needed to distinguish scalar (8B) from str (16B) globals
// when picking the load/store sequence.
type letvar = struct {
	name:   str,
	tnode:  *node,
	lvnext: *letvar,
};

fn cgeninit(c: *cgen, a: *arena) void = {
	c.a = a;
	c.locals = nil;
	c.frame = 0;
	c.lastwasreturn = 0;
	c.labelseq = 0;
	c.varargseq = 0;
	c.tagscrsz = 0;
	c.retscroff = 0;
	c.sretargoff = 0;
	c.sretdestoff = 0;
	c.sretscroff = 0;
	c.sretscrsz = 0;
	c.sretforward = 0;
	// Note: strlit_seq, strlits, ffis are *not* reset here; they
	// persist across cgfn calls within one file. cgfile resets them
	// at the start of each compilation unit.
	c.looptop = 0;
	c.loopendbuf  = amalloc(a, (LOOP_MAX: u64) * 16u64): *str;
	c.loopcontbuf = amalloc(a, (LOOP_MAX: u64) * 16u64): *str;
	c.yieldtop = 0;
	c.yieldbuf = amalloc(a, (LOOP_MAX: u64) * 16u64): *str;
	c.defertop = 0;
	c.deferbuf = amalloc(a, (DEFER_MAX: u64) * 8u64): **node;
};

// localalloc — append a slot for `name` without dedup. Used for
// match-arm bindings, which C cgen allocates via cgexpr's by-value
// `locals` list — so two separate matches each get fresh slots even
// when their bind names collide. scanlocals follows the same rule
// for nkind.N_MCASE.
fn localalloc(c: *cgen, name: str, sz: i32, tnode: *node) i32 = {
	let asz: i32 = sz;
	if (asz < 8) { asz = 8; };
	if ((asz & 7) != 0) { asz = (asz + 7) & ~7; };
	c.frame += asz;
	let off: i32 = 0 - c.frame;
	let l: *local = amalloc(c.a, 48u64): *local;
	l.name = name;
	l.off = off;
	l.tnode = tnode;
	l.lnext = c.locals;
	c.locals = l;
	return off;
};

// localaddstack — register a param at a positive BP offset. Used for
// args that overflow the 6 SysV int / 8 float reg windows; the caller
// pushes them in reverse, so each spilled arg lives at 16(BP), 24(BP),
// etc. (after the saved RIP+BP). No spill instruction is emitted; the
// slot IS the caller's stack slot.
fn localaddstack(c: *cgen, name: str, tnode: *node, off: i32) void = {
	let l: *local = amalloc(c.a, 48u64): *local;
	l.name = name;
	l.off = off;
	l.tnode = tnode;
	l.lnext = c.locals;
	c.locals = l;
};

fn localadd(c: *cgen, name: str, sz: i32, tnode: *node) i32 = {
	// User-let path (post-#27): always allocate a fresh slot per
	// binding. Pre-fix this deduped by name to share one slot
	// across same-name lets in disjoint scopes — inherited from
	// C cgen's localoff. Both stages had the same silent-stack-
	// corruption bug: an inner 8B `let a: i64` allocated first
	// would force a later outer `let a: [128]u8` onto the 8B slot,
	// and `a[127]` would write at +119(BP), past the saved RIP.
	// Localfind walks head-first, so the most-recent binding still
	// wins lookups inside its scope. Tnode is carried on the
	// freshly-pushed entry, so type dispatch in cgenutil never
	// sees a stale predecessor.
	//
	// Synthetic scratch slots (`@tagscr`, `@retscr`, `@tagbase`)
	// keep the per-fn dedup. Each scratch is sized identically
	// across its call sites and intended to be shared — the
	// scanlocals pre-pass also dedups via scanseenmark, so frame
	// reservation and emit-time allocation stay in sync. The
	// `@`-prefix carve-out preserves that contract; user names
	// can never start with `@` (lexer-rejected).
	//
	// @retscr (#14) routes through c.retscroff instead of c.locals.
	// The c.locals-based dedup is unwound by cgblock save/restore
	// (post-#27): a return inside an `if` block adds @retscr to
	// c.locals; on block exit, c.locals reverts and a sibling/outer
	// return reallocates a fresh slot. Scan had reserved one slot;
	// emit grew the frame past the reservation and the second
	// site's writes landed below SP. c.retscroff is per-fn state
	// that survives cgblock save/restore and pins single-slot.
	if (name.len > 0) {
		if (name[0] == 64u8) {	// '@'
			if (streq(name, "@retscr")) {
				if (c.retscroff != 0) { return c.retscroff; };
				let off: i32 = localalloc(c, name, sz, tnode);
				c.retscroff = off;
				return off;
			};
			// @sretarg / @sretscr (#23): same single-slot SSoT
			// pattern as @retscr. @sretarg holds the saved hidden
			// RDI for sret callees (8B, set once per fn at the
			// prologue); @sretscr is the caller-side discard slot
			// for sret CALLs whose result is dropped.
			if (streq(name, "@sretarg")) {
				if (c.sretargoff != 0) { return c.sretargoff; };
				let off: i32 = localalloc(c, name, sz, tnode);
				c.sretargoff = off;
				return off;
			};
			if (streq(name, "@sretscr")) {
				if (c.sretscroff != 0) { return c.sretscroff; };
				let off: i32 = localalloc(c, name, sz, tnode);
				c.sretscroff = off;
				return off;
			};
			let cur: *local = c.locals;
			for (cur != nil) {
				let cn: str = cur.name;
				if (streq(cn, name)) {
					cur.tnode = tnode;
					return cur.off;
				};
				cur = cur.lnext;
			};
		};
	};
	return localalloc(c, name, sz, tnode);
};

// scanseenmark — called by scanlocals on every let / match-bind
// site. Returns true if `name` is already tracked in c.locals (so
// the slot will be shared at emission time — no new frame bump).
// Otherwise appends a name-only stub and returns false. Stubs are
// thrown away when cgfn resets c.locals before emission.
fn scanseenmark(c: *cgen, name: str) bool = {
	if (localfindnode(c, name) != nil) { return true; };
	let l: *local = amalloc(c.a, 48u64): *local;
	l.name = name;
	l.off = 0;
	l.tnode = nil;
	l.lnext = c.locals;
	c.locals = l;
	return false;
};

fn localfindnode(c: *cgen, name: str) *local = {
	let l: *local = c.locals;
	for (l != nil) {
		let ln: str = l.name;
		if (streq(ln, name)) { return l; };
		l = l.lnext;
	};
	return nil;
};

fn localfind(c: *cgen, name: str) i32 = {
	let l: *local = c.locals;
	for (l != nil) {
		let ln: str = l.name;
		if (ln.len == name.len) {
			let i: i32 = 0;
			let eq: bool = true;
			for (i < name.len) {
				if (ln[i] != name[i]) { eq = false; i = name.len; }
				else { i += 1; };
			};
			if (eq) { return l.off; };
		};
		l = l.lnext;
	};
	return 0;
};

// ---- emit helpers ---------------------------------------------------

fn emitline(s: str) void = { os.write(1, s.ptr, s.len: u64); };

fn emitint(v: i64) void = {
	let s: str = strconv.i64tos(v, strconv.base.DEC);
	os.write(1, s.ptr, s.len: u64);
};

fn emituint(v: u64) void = {
	let s: str = strconv.u64tos(v, strconv.base.DEC);
	os.write(1, s.ptr, s.len: u64);
};

// emitdispreg — print "disp(reg)" or "(reg)" when disp == 0, the
// way Plan 9 6c/6a do.
fn emitdispreg(off: i64, reg: str) void = {
	if (off != 0i64) { emitint(off); };
	emitline("(");
	emitline(reg);
	emitline(")");
};

// emitoff — print an integer offset, suppressing it entirely when 0.
// Use before any emitline("(BP)...") or emitline("(SB)...") sequence.
// Plan 9 cc convention: "(BP)" not "0(BP)".
fn emitoff(v: i64) void = {
	if (v != 0i64) { emitint(v); };
};

// mklabel — fresh label "<fnname>_<prefix>_<seq>". Returns an
// arena-owned str. Mirrors C cgen's mklabel so diffs match.
fn mklabel(c: *cgen, prefix: str) str = {
	let buf: [128]u8;
	let i: i32 = 0;
	let fname: str = c.fnname;
	let j: i32 = 0;
	for (j < fname.len) {
		buf[i] = fname[j];
		i += 1; j += 1;
	};
	buf[i] = 95u8; i += 1;	// '_'
	j = 0;
	for (j < prefix.len) {
		buf[i] = prefix[j];
		i += 1; j += 1;
	};
	buf[i] = 95u8; i += 1;	// '_'
	let ns: str = strconv.i64tos(c.labelseq: i64, strconv.base.DEC);
	let n: i32 = ns.len;
	let dk: i32 = 0;
	for (dk < n) { buf[i + dk] = ns.ptr[dk]; dk += 1; };
	c.labelseq += 1;
	let total: i32 = i + n;
	let p: *u8 = amalloc(c.a, (total: u64) + 1u64): *u8;
	let k: i32 = 0;
	for (k < total) {
		p[k] = buf[k];
		k += 1;
	};
	p[total] = 0u8;
	let r: str;
	r.ptr = p;
	r.len = total;
	return r;
};

fn emitlabel(s: str) void = {
	os.write(1, s.ptr, s.len: u64);
	emitline(":\n");
};

// mkscratchname — fresh local-slot name ".<prefix>_<labelseq>". Used for
// compiler-synthesised slots (switch scrutinee, forrange index/len)
// that need to be unique per use site but are never referenced by user
// code. Increments labelseq so the same source position lines up with
// C cgen's labelseq stream.
fn mkscratchname(c: *cgen, prefix: str) str = {
	let buf: [128]u8;
	let i: i32 = 0;
	buf[i] = 46u8; i += 1;	// '.'
	let j: i32 = 0;
	for (j < prefix.len) {
		buf[i] = prefix[j];
		i += 1; j += 1;
	};
	buf[i] = 95u8; i += 1;	// '_'
	let ns: str = strconv.i64tos(c.labelseq: i64, strconv.base.DEC);
	let n: i32 = ns.len;
	let dk: i32 = 0;
	for (dk < n) { buf[i + dk] = ns.ptr[dk]; dk += 1; };
	c.labelseq += 1;
	let total: i32 = i + n;
	let p: *u8 = amalloc(c.a, (total: u64) + 1u64): *u8;
	let k: i32 = 0;
	for (k < total) {
		p[k] = buf[k];
		k += 1;
	};
	p[total] = 0u8;
	let r: str;
	r.ptr = p;
	r.len = total;
	return r;
};

// ---- string interning ------------------------------------------------
//
// streq is provided by sym.ww and reused here.

// internstrlit — return a stable label for `bytes`. Dedups by content
// so identical literals share storage.
fn internstrlit(c: *cgen, bytes: str) str = {
	let s: *strlit = c.strlits;
	for (s != nil) {
		let bs: str = s.bytes;
		if (streq(bs, bytes)) {
			return s.label;
		};
		s = s.slnext;
	};
	// New label "_S_<seq>".
	let buf: [32]u8;
	buf[0] = 95u8; buf[1] = 83u8; buf[2] = 95u8;	// "_S_"
	let ns: str = strconv.i64tos(c.strlitseq: i64, strconv.base.DEC);
	let n: i32 = ns.len;
	let dk: i32 = 0;
	for (dk < n) { buf[3 + dk] = ns.ptr[dk]; dk += 1; };
	c.strlitseq += 1;
	let total: i32 = 3 + n;
	let p: *u8 = amalloc(c.a, (total: u64) + 1u64): *u8;
	let i: i32 = 0;
	for (i < total) { p[i] = buf[i]; i += 1; };
	p[total] = 0u8;
	let lab: str;
	lab.ptr = p;
	lab.len = total;
	let nw: *strlit = amalloc(c.a, 48u64): *strlit;
	nw.label = lab;
	nw.bytes = bytes;
	nw.slnext = c.strlits;
	c.strlits = nw;
	return lab;
};

// letscalarprim — recognise the bare type-name keywords whose values
// fit in an 8-byte .data slot and load back with a plain MOVQ. Float
// types are handled separately by letfloatprim — they need MOVSS/MOVSD
// and use 4-byte (f32) or 8-byte (f64) slots.
fn letscalarprim(nm: str) bool = {
	if (streq(nm, "bool")) { return true; };
	if (streq(nm, "rune")) { return true; };
	if (streq(nm, "i8"))   { return true; };
	if (streq(nm, "i16"))  { return true; };
	if (streq(nm, "i32"))  { return true; };
	if (streq(nm, "i64"))  { return true; };
	if (streq(nm, "u8"))   { return true; };
	if (streq(nm, "u16"))  { return true; };
	if (streq(nm, "u32"))  { return true; };
	if (streq(nm, "u64"))  { return true; };
	if (streq(nm, "int"))  { return true; };
	if (streq(nm, "uint")) { return true; };
	if (streq(nm, "uintptr")) { return true; };
	return false;
};

// letfloatprim — float type-name keywords. f32 → 4B slot, f64 → 8B.
// Returns the slot size or 0 if not a float type.
fn letfloatprim(nm: str) i32 = {
	if (streq(nm, "f32")) { return 4; };
	if (streq(nm, "f64")) { return 8; };
	return 0;
};

// letemitsize — slot size in bytes for a top-level `let`, or 0 if
// the type isn't yet supported as a writable global. Walks type
// aliases so byte output matches C cgen, which resolves Type kinds.
//   4       → f32    (literal init supported)
//   8       → scalar or f64 (literal init supported)
//   16      → str    (only zero-init / nil / "" supported)
//   24      → slice  (only zero-init supported)
//   varies  → struct (zero-init only; field reads/scalar-field writes)
fn letemitsize(c: *cgen, d: *node) i32 = {
	if (d == nil) { return 0; };
	let t: *node = d.lhs;
	for (t != nil) {
		if (t.kind == nkind.N_TPTR) { return 8; };
		if (t.kind == nkind.N_TSLICE) { return 24; };
		if (t.kind == nkind.N_TARRAY) {
			let lenn: *node = t.rhs;
			let elemn: *node = t.lhs;
			let alen: i32 = 1;
			if (lenn != nil) {
				if (lenn.kind == nkind.N_INTLIT) { alen = lenn.uval: i32; };
			};
			let esz: i32 = 8;
			if (elemn != nil) {
				if (elemn.kind == nkind.N_TNAME) {
					let ps: i32 = primsize(elemn.str);
					if (ps > 0) { esz = ps; };
				};
			};
			return alen * esz;
		};
		if (t.kind != nkind.N_TNAME) { return 0; };
		let nm: str = t.str;
		if (letscalarprim(nm)) { return 8; };
		let fsz: i32 = letfloatprim(nm);
		if (fsz > 0) { return fsz; };
		if (streq(nm, "str")) { return 16; };
		let si: *structinfo = structlookup(c, nm);
		if (si != nil) { return si.totsize; };
		let next: *node = aliaslookup(c, nm);
		if (next == nil) { return 0; };
		t = next;
	};
	return 0;
};

fn collectlets(c: *cgen, file: *node) void = {
	c.lets = nil;
	if (file == nil) { return; };
	let d: *node = file.list;
	for (d != nil) {
		if (d.kind == nkind.N_LET) {
			let nm: str = d.str;
			if (nm.len > 0) {
				if (letemitsize(c, d) > 0) {
					let lv: *letvar = amalloc(c.a, 48u64): *letvar;
					lv.name   = nm;
					lv.tnode  = d.lhs;
					lv.lvnext = c.lets;
					c.lets    = lv;
				};
			};
		};
		d = d.next;
	};
};

fn isletvar(c: *cgen, name: str) bool = {
	let lv: *letvar = c.lets;
	for (lv != nil) {
		if (streq(lv.name, name)) { return true; };
		lv = lv.lvnext;
	};
	return false;
};

// letvarisstr — is the named top-level let a str global? Resolves
// aliases to mirror C cgen's `let_isstr`. Used by cgident/cgdot/
// cgassign to pick the (LEAQ, MOVQ, MOVQ) sequence over the bare
// MOVQ scalar load.
// letvartnode — direct lookup of a top-level let's tnode. Used by
// cgindex / cgassign to detect global `[N]T` arrays and `*T`
// pointers, where the addressing path needs LEAQ name(SB) (array)
// or MOVQ name(SB) (pointer) and the element size from T.
fn letvartnode(c: *cgen, name: str) *node = {
	let lv: *letvar = c.lets;
	for (lv != nil) {
		if (streq(lv.name, name)) { return lv.tnode; };
		lv = lv.lvnext;
	};
	return nil;
};

fn letvarisstr(c: *cgen, name: str) bool = {
	let lv: *letvar = c.lets;
	for (lv != nil) {
		if (streq(lv.name, name)) {
			let t: *node = lv.tnode;
			for (t != nil) {
				if (t.kind != nkind.N_TNAME) { return false; };
				let nm: str = t.str;
				if (streq(nm, "str")) { return true; };
				let nx: *node = aliaslookup(c, nm);
				if (nx == nil) { return false; };
				t = nx;
			};
			return false;
		};
		lv = lv.lvnext;
	};
	return false;
};

// letvarisslice — is the named top-level let a slice global?
// Slice headers are 24 bytes; the ABI flows as (AX, BX, CX) so the
// load sequence ends with `MOVQ 16(CX), CX` (overwrites the
// address holder with the cap). Mirrors C cgen's `let_isslice`.
fn letvarisslice(c: *cgen, name: str) bool = {
	let lv: *letvar = c.lets;
	for (lv != nil) {
		if (streq(lv.name, name)) {
			let t: *node = lv.tnode;
			if (t == nil) { return false; };
			if (t.kind == nkind.N_TSLICE) { return true; };
			return false;
		};
		lv = lv.lvnext;
	};
	return false;
};

// letvarisfloat — slot size for a named float global, or 0 if not
// a float-typed let. Walks aliases so the byte-identity contract
// matches C cgen's `let_isfloat` (which resolves Type kinds).
fn letvarisfloat(c: *cgen, name: str) i32 = {
	let lv: *letvar = c.lets;
	for (lv != nil) {
		if (streq(lv.name, name)) {
			let t: *node = lv.tnode;
			for (t != nil) {
				if (t.kind != nkind.N_TNAME) { return 0; };
				let fsz: i32 = letfloatprim(t.str);
				if (fsz > 0) { return fsz; };
				let nx: *node = aliaslookup(c, t.str);
				if (nx == nil) { return 0; };
				t = nx;
			};
			return 0;
		};
		lv = lv.lvnext;
	};
	return 0;
};

// letvarisstruct — is the named top-level let a struct global?
// Struct globals use LEAQ name(SB), CX as the field-access base; the
// cgdot read and cgassign write paths branch on this to skip the
// frame-relative addressing they use for locals.
fn letvarisstruct(c: *cgen, name: str) bool = {
	let lv: *letvar = c.lets;
	for (lv != nil) {
		if (streq(lv.name, name)) {
			let t: *node = lv.tnode;
			for (t != nil) {
				if (t.kind != nkind.N_TNAME) { return false; };
				let nm: str = t.str;
				if (structlookup(c, nm) != nil) { return true; };
				let nx: *node = aliaslookup(c, nm);
				if (nx == nil) { return false; };
				t = nx;
			};
			return false;
		};
		lv = lv.lvnext;
	};
	return false;
};

// letvarstructinfo — for a struct global, return its structinfo
// so the cgdot/cgassign paths can look up fields. nil if the let
// isn't a struct (or wasn't found).
fn letvarstructinfo(c: *cgen, name: str) *structinfo = {
	let lv: *letvar = c.lets;
	for (lv != nil) {
		if (streq(lv.name, name)) {
			let t: *node = lv.tnode;
			for (t != nil) {
				if (t.kind != nkind.N_TNAME) { return nil; };
				let nm: str = t.str;
				let si: *structinfo = structlookup(c, nm);
				if (si != nil) { return si; };
				let nx: *node = aliaslookup(c, nm);
				if (nx == nil) { return nil; };
				t = nx;
			};
			return nil;
		};
		lv = lv.lvnext;
	};
	return nil;
};

// emitdatawbyte — write one byte of an asm string literal using
// the same escape rules as emitdefconstants / emitdatasection.
fn emitdatawbyte(b: u8) void = {
	if (b == 34u8) { emitline("\\\""); return; };
	if (b == 92u8) { emitline("\\\\"); return; };
	if (b < 32u8) {
		emitline("\\x");
		let hi: u8 = b >> 4u8;
		let lo: u8 = b & 15u8;
		let bb: [2]u8;
		if (hi < 10u8) { bb[0] = hi + 48u8; }
		else { bb[0] = (hi - 10u8) + 97u8; };
		if (lo < 10u8) { bb[1] = lo + 48u8; }
		else { bb[1] = (lo - 10u8) + 97u8; };
		os.write(1, bb.ptr, 2u64);
		return;
	};
	if (b >= 127u8) {
		emitline("\\x");
		let hi: u8 = b >> 4u8;
		let lo: u8 = b & 15u8;
		let bb: [2]u8;
		if (hi < 10u8) { bb[0] = hi + 48u8; }
		else { bb[0] = (hi - 10u8) + 97u8; };
		if (lo < 10u8) { bb[1] = lo + 48u8; }
		else { bb[1] = (lo - 10u8) + 97u8; };
		os.write(1, bb.ptr, 2u64);
		return;
	};
	let bb: [1]u8;
	bb[0] = b;
	os.write(1, bb.ptr, 1u64);
};

// letpreintern — intern strlits referenced from top-level str-let
// initialisers BEFORE emitdatasection runs. Mirrors cmd/w6c/cgen.c
// let_pre_intern: emitletdataw later looks up the same label, and
// emitdatasection emits the DATA row in the same .s file. Running
// emitletdataw after emitdatasection would flip the (DATA strlits,
// DATAW lets) section order and break byte-identity.
export fn letpreintern(c: *cgen, file: *node) void = {
	if (file == nil) { return; };
	let d: *node = file.list;
	for (d != nil) {
		if (d.kind == nkind.N_LET) {
			let sz: i32 = letemitsize(c, d);
			if (sz == 16) {
				let r: *node = d.rhs;
				for (r != nil) {
					if (r.kind != nkind.N_CAST) { break; };
					r = r.lhs;
				};
				if (r != nil) {
					if (r.kind == nkind.N_STRLIT) {
						if (r.str.len > 0) {
							internstrlit(c, r.str);
						};
					};
				};
			};
		};
		d = d.next;
	};
};

// emitletdataw — DATAW directive per top-level `let` global.
//   8B  scalar with int/rune/bool/nil literal init (or no init).
//   16B str — no init / `nil` / `""` → 16 zero bytes; or non-empty
//        strlit init → 8 zero placeholder + 8 LE len bytes plus a
//        DATAR slot+0,strlit reloc that the linker patches at load.
//   sz  struct — zero only.
// Non-literal scalar inits and unsupported shapes are skipped so the
// link surfaces an undefined-symbol error if the binding is used.
fn emitletdataw(c: *cgen, file: *node) void = {
	let d: *node = file.list;
	for (d != nil) {
		if (d.kind == nkind.N_LET) {
			let nm: str = d.str;
			if (nm.len > 0) {
				let sz: i32 = letemitsize(c, d);
				let issg: bool = letvarisstruct(c, nm);
				let fsz: i32 = letvarisfloat(c, nm);
				if (fsz > 0) {
					// Float global: 4B (f32) or 8B (f64).
					// Two init shapes:
					//   - no rhs: emit fsz zero bytes
					//   - N_FLOATLIT: bake the IEEE bits the
					//     parser stashed in r.uval (lexer
					//     bit-casts t.fval into t.uval). f32
					//     emits the low 4 bytes; f64 emits 8.
					let bits: u64 = 0u64;
					let ok: bool = true;
					if (d.rhs != nil) {
						let r: *node = d.rhs;
						for (r != nil) {
							if (r.kind != nkind.N_CAST) { break; };
							r = r.lhs;
						};
						ok = false;
						if (r != nil) {
							if (r.kind == nkind.N_FLOATLIT) {
								bits = r.uval;
								ok = true;
							};
						};
					};
					if (ok) {
						emitline("DATAW ");
						emitsymname(c, nm);
						emitline("(SB),\"");
						let i: i32 = 0;
						let nb: u64 = bits;
						for (i < fsz) {
							emitdatawbyte((nb & 255u64): u8);
							nb = nb >> 8u64;
							i += 1;
						};
						emitline("\"\n");
					};
				};
				// Skip the scalar 8B path when the global is a
				// fixed-size array that just happens to sum to 8
				// bytes (e.g. [4]u16, [8]u8) — the array path
				// below handles it and the duplicate DATAW would
				// otherwise differ across stages on user code.
				let isarr8: bool = false;
				if (d.lhs != nil) {
					if (d.lhs.kind == nkind.N_TARRAY) { isarr8 = true; };
				};
				if (sz == 8 && !issg && fsz == 0 && !isarr8) {
					let v: u64 = 0u64;
					let ok: bool = true;
					if (d.rhs != nil) {
						let r: *node = d.rhs;
						for (r != nil) {
							if (r.kind != nkind.N_CAST) { break; };
							r = r.lhs;
						};
						// Same helper as emitdefconstants (#24)
						// — widens the gate so N_UN over an
						// int leaf folds. `let x: i8 = -1i8;`
						// arrives as N_UN(TK_MINUS, N_INTLIT)
						// after the typed-AST cast peel.
						ok = foldintliteral(r, &v);
					};
					if (ok) {
						emitline("DATAW ");
						emitsymname(c, nm);
						emitline("(SB),\"");
						let i: i32 = 0;
						let n: u64 = v;
						for (i < 8) {
							let b: u8 = (n & 255u64): u8;
							n = n >> 8u64;
							emitdatawbyte(b);
							i += 1;
						};
						emitline("\"\n");
					};
				};
				if (sz == 16 && !issg) {
					let r: *node = d.rhs;
					for (r != nil) {
						if (r.kind != nkind.N_CAST) { break; };
						r = r.lhs;
					};
					// str-literal init (non-empty): emit
					// the 16B payload as 8 placeholder zero
					// bytes + 8 LE bytes of length, then a
					// DATAR reloc to patch the ptr half with
					// the strlit's runtime VA.
					let strlitinit: bool = false;
					if (r != nil) {
						if (r.kind == nkind.N_STRLIT) {
							if (r.str.len > 0) { strlitinit = true; };
						};
					};
					if (strlitinit) {
						let lab: str = internstrlit(c, r.str);
						let v: u64 = r.str.len: u64;
						emitline("DATAW ");
						emitsymname(c, nm);
						emitline("(SB),\"");
						let i: i32 = 0;
						for (i < 8) { emitdatawbyte(0u8); i += 1; };
						i = 0;
						let nv: u64 = v;
						for (i < 8) {
							emitdatawbyte((nv & 255u64): u8);
							nv = nv >> 8u64;
							i += 1;
						};
						emitline("\"\n");
						emitline("DATAR ");
						emitsymname(c, nm);
						emitline("+0(SB),");
						os.write(1, lab.ptr, lab.len: u64);
						emitline("(SB)\n");
					} else {
						// zero-init: accept no rhs, nil,
						// or empty strlit.
						let ok: bool = true;
						if (d.rhs != nil) {
							ok = false;
							if (r != nil) {
								if (r.kind == nkind.N_NIL) { ok = true; };
								if (r.kind == nkind.N_STRLIT) {
									if (r.str.len == 0) { ok = true; };
								};
							};
						};
						if (ok) {
							emitline("DATAW ");
							emitsymname(c, nm);
							emitline("(SB),\"");
							let i: i32 = 0;
							for (i < 16) {
								emitdatawbyte(0u8);
								i += 1;
							};
							emitline("\"\n");
						};
					};
				};
				if (sz == 24 && !issg) {
					// Slice: zero-init only (no slice-literal
					// syntax to honour). Any rhs other than
					// `nil` is skipped → undefined symbol at
					// link.
					let ok: bool = true;
					if (d.rhs != nil) {
						let r: *node = d.rhs;
						for (r != nil) {
							if (r.kind != nkind.N_CAST) { break; };
							r = r.lhs;
						};
						ok = false;
						if (r != nil) {
							if (r.kind == nkind.N_NIL) { ok = true; };
						};
					};
					if (ok) {
						emitline("DATAW ");
						emitsymname(c, nm);
						emitline("(SB),\"");
						let i: i32 = 0;
						for (i < 24) {
							emitdatawbyte(0u8);
							i += 1;
						};
						emitline("\"\n");
					};
				};
				// Struct globals — any size, zero-init only.
				// A struct literal init isn't compile-time
				// evaluated yet; skip and the link will surface
				// an undefined-symbol error if referenced.
				if (issg) {
					if (d.rhs == nil) {
						emitline("DATAW ");
						emitsymname(c, nm);
						emitline("(SB),\"");
						let i: i32 = 0;
						for (i < sz) {
							emitdatawbyte(0u8);
							i += 1;
						};
						emitline("\"\n");
					};
				};
				// Top-level `[N]T = [a, b, ...]` array global.
				// Emits N*esz bytes with each element's bytes
				// little-endian for the declared primitive width.
				// Element fold goes through foldintliteral (same
				// helper as emitdefconstants / scalar arm above)
				// so `-1i8` and friends emit their two's-complement
				// bytes after the leading N_CAST peel — pre-#19
				// this arm only matched bare N_INTLIT/N_RUNELIT and
				// silently emitted zero for unfoldable elements.
				// `...` (N_FIELD with str="...") repeats the last
				// folded value across the remaining slots.
				if (d.lhs != nil) {
					if (d.lhs.kind == nkind.N_TARRAY) {
						let elemn: *node = d.lhs.lhs;
						let esz: i32 = 8;
						if (elemn != nil) {
							if (elemn.kind == nkind.N_TNAME) {
								let ps: i32 = primsize(elemn.str);
								if (ps > 0) { esz = ps; };
							};
						};
						let total: i32 = sz;
						let alen: i32 = total / esz;
						let elems: *node = nil;
						if (d.rhs != nil) {
							if (d.rhs.kind == nkind.N_ARRLIT) {
								elems = d.rhs.list;
							};
						};
						emitline("DATAW ");
						emitsymname(c, nm);
						emitline("(SB),\"");
						let i: i32 = 0;
						let e: *node = elems;
						let last: u64 = 0u64;
						let inrepeat: bool = false;
						for (i < alen) {
							let v: u64 = last;
							if (!inrepeat && e != nil) {
								if (e.kind == nkind.N_FIELD) {
									if (streq(e.str, "...")) {
										inrepeat = true;
									} else {
										e = e.next;
									};
								} else {
									let ev: *node = e;
									for (ev != nil) {
										if (ev.kind != nkind.N_CAST) { break; };
										ev = ev.lhs;
									};
									if (!foldintliteral(ev, &v)) { v = 0u64; };
									last = v;
									e = e.next;
								};
							};
							let nb: u64 = v;
							let b: i32 = 0;
							for (b < esz) {
								emitdatawbyte((nb & 255u64): u8);
								nb = nb >> 8u64;
								b += 1;
							};
							i += 1;
						};
						emitline("\"\n");
					};
				};
			};
		};
		d = d.next;
	};
};

// emitdefconstants — DATA directive per top-level fold-to-literal
// `def`. 8 bytes little-endian to match what the C cgen emits.
// foldintliteral gates: int/rune literal, true/false/nil, and a
// unary +/-/~ over the same. `def NEG: i32 = -100;` arrives as
// N_UN(TK_MINUS, N_INTLIT) — the unary peel is exactly what the
// gate is for.
fn emitdefconstants(c: *cgen, file: *node) void = {
	let d: *node = file.list;
	for (d != nil) {
		if (d.kind == nkind.N_DEF) {
			let r: *node = d.rhs;
			let v: u64 = 0u64;
			let ok: bool = false;
			if (r != nil) {
				ok = foldintliteral(r, &v);
			};
			if (ok) {
				emitline("DATA ");
				if (d.exported == 0) {
					if (d.module.len > 0) {
						os.write(1, d.module.ptr, d.module.len: u64);
						os.write(1, ".".ptr, 1u64);
					};
				};
				let nm: str = d.str;
				os.write(1, nm.ptr, nm.len: u64);
				emitline("(SB),\"");
				let i: i32 = 0;
				let n: u64 = v;
				for (i < 8) {
					let b: u8 = (n & 255u64): u8;
					n = n >> 8u64;
					// C emit_defs only special-cases " and \;
					// every other non-printable goes as \xHH.
					if (b == 34u8) { emitline("\\\""); }
					else { if (b == 92u8) { emitline("\\\\"); }
					else {
						if (b < 32u8) {
							emitline("\\x");
							let hi: u8 = b >> 4u8;
							let lo: u8 = b & 15u8;
							let bb: [2]u8;
							if (hi < 10u8) { bb[0] = hi + 48u8; }
							else { bb[0] = (hi - 10u8) + 97u8; };
							if (lo < 10u8) { bb[1] = lo + 48u8; }
							else { bb[1] = (lo - 10u8) + 97u8; };
							os.write(1, bb.ptr, 2u64);
						} else {
							if (b >= 127u8) {
								emitline("\\x");
								let hi: u8 = b >> 4u8;
								let lo: u8 = b & 15u8;
								let bb: [2]u8;
								if (hi < 10u8) { bb[0] = hi + 48u8; }
								else { bb[0] = (hi - 10u8) + 97u8; };
								if (lo < 10u8) { bb[1] = lo + 48u8; }
								else { bb[1] = (lo - 10u8) + 97u8; };
								os.write(1, bb.ptr, 2u64);
							} else {
								let bb: [1]u8;
								bb[0] = b;
								os.write(1, bb.ptr, 1u64);
							};
						};
					};};
					i += 1;
				};
				emitline("\"\n");
			};
		};
		d = d.next;
	};
};

// emitdatasection — DATA directives for every interned strlit.
// Trailing NUL appended so .ptr can be used as a C string by syscalls.
fn emitdatasection(c: *cgen) void = {
	let s: *strlit = c.strlits;
	for (s != nil) {
		emitline("DATA ");
		let lab: str = s.label;
		os.write(1, lab.ptr, lab.len: u64);
		emitline("(SB),\"");
		let bs: str = s.bytes;
		let i: i32 = 0;
		for (i < bs.len) {
			let b: u8 = bs[i];
			if (b == 34u8) { emitline("\\\""); }	// "
			else { if (b == 92u8) { emitline("\\\\"); }	// \
			else { if (b == 10u8) { emitline("\\n"); }
			else { if (b == 9u8)  { emitline("\\t"); }
			else { if (b == 13u8) { emitline("\\r"); }
			else {
				if (b < 32u8) {
					emitline("\\x");
					let hi: u8 = b >> 4u8;
					let lo: u8 = b & 15u8;
					let bb: [2]u8;
					if (hi < 10u8) { bb[0] = hi + 48u8; }
					else { bb[0] = (hi - 10u8) + 97u8; };
					if (lo < 10u8) { bb[1] = lo + 48u8; }
					else { bb[1] = (lo - 10u8) + 97u8; };
					os.write(1, bb.ptr, 2u64);
				} else {
					if (b >= 127u8) {
						emitline("\\x");
						let hi: u8 = b >> 4u8;
						let lo: u8 = b & 15u8;
						let bb: [2]u8;
						if (hi < 10u8) { bb[0] = hi + 48u8; }
						else { bb[0] = (hi - 10u8) + 97u8; };
						if (lo < 10u8) { bb[1] = lo + 48u8; }
						else { bb[1] = (lo - 10u8) + 97u8; };
						os.write(1, bb.ptr, 2u64);
					} else {
						let bb: [1]u8;
						bb[0] = b;
						os.write(1, bb.ptr, 1u64);
					};
				};
			};};};};};
			i += 1;
		};
		emitline("\\x00\"\n");
		s = s.slnext;
	};
};

// ---- fn return-type map ---------------------------------------------
//
// Per-file: ident → ret-type-node. Used to decide whether to shuffle
// (AX, DX) → (AX, BX) after a CALL — needed for str-returning fns so
// the value flows through cgen as the canonical (AX, BX) str pair.

type fnret = struct {
	fname: str,
	fmod:  str,
	rtype: *node,
	params: *node,
	frnext: *fnret,
};

fn collectfnrets(c: *cgen, file: *node) void = {
	c.fnrets = nil;
	let d: *node = file.list;
	for (d != nil) {
		if (d.kind == nkind.N_FNDECL) {
			let f: *fnret = amalloc(c.a, 64u64): *fnret;
			f.fname = d.str;
			f.fmod = d.module;
			f.rtype = d.lhs;
			f.params = d.list;
			f.frnext = c.fnrets;
			c.fnrets = f;
		};
		d = d.next;
	};
};

fn fnretlookup(c: *cgen, name: str) *node = {
	let f: *fnret = c.fnrets;
	for (f != nil) {
		let fn_: str = f.fname;
		if (streq(fn_, name)) { return f.rtype; };
		f = f.frnext;
	};
	return nil;
};

// fnretlookupmod — same-module-first walk. Module-qualified `mod.fn(...)`
// callees route here so a leaf collision (same fn name exported from
// multiple modules) resolves to the explicit module. Falls back to the
// first leaf match if no matching module is registered. Mirror of
// fnparamslookupmod (#28); without this, matchscrutt's N_DOT branch
// picks the last-declared `next` regardless of qualifier, so a 4-arm
// `match (utf8.next(d))` inside a `fn next() (rune | done)` resolves
// the scrutinee tagged type to `(rune | done)` — flatvariantidx then
// can't see arms 2/3 and collapses them onto tag 0 (task #31).
fn fnretlookupmod(c: *cgen, name: str, mod: str) *node = {
	if (mod.len > 0) {
		let f: *fnret = c.fnrets;
		for (f != nil) {
			if (streq(f.fname, name)) {
				if (streq(f.fmod, mod)) { return f.rtype; };
			};
			f = f.frnext;
		};
	};
	return fnretlookup(c, name);
};

// fnparamslookup — head of the declared param-list for a fn, or nil
// if the name isn't a registered fn. Used by cgcall / pushargsrev to
// detect implicit widening from a concrete variant into a tagged-union
// parameter slot.
fn fnparamslookup(c: *cgen, name: str) *node = {
	let f: *fnret = c.fnrets;
	for (f != nil) {
		if (streq(f.fname, name)) { return f.params; };
		f = f.frnext;
	};
	return nil;
};

// fnparamslookupmod — same-module-first leaf walk. Module-qualified
// `mod.fn(...)` calls go through this so a leaf collision (multiple
// modules export the same name, e.g. `os.read` and `io.read`) resolves
// to the explicit module. Falls back to the first leaf match if no
// matching module is registered — mirrors aliaslookup's two-pass shape
// (cgen.ww:75, fixed in #27).
fn fnparamslookupmod(c: *cgen, name: str, mod: str) *node = {
	if (mod.len > 0) {
		let f: *fnret = c.fnrets;
		for (f != nil) {
			if (streq(f.fname, name)) {
				if (streq(f.fmod, mod)) { return f.params; };
			};
			f = f.frnext;
		};
	};
	return fnparamslookup(c, name);
};

// ---- def-constant registry ------------------------------------------
//
// `def NAME: T = LIT;` becomes a DATA symbol the C-side w6c emits; an
// ident reference loads it via `MOVQ NAME(SB), AX`. We collect them at
// file load and consult on nkind.N_IDENT lookup.

type defent = struct {
	dname: str,
	drhs:  *node,
	dnext: *defent,
};

fn collectdefs(c: *cgen, file: *node) void = {
	c.defs = nil;
	let d: *node = file.list;
	for (d != nil) {
		if (d.kind == nkind.N_DEF) {
			let e: *defent = amalloc(c.a, 32u64): *defent;
			e.dname = d.str;
			e.drhs  = d.rhs;
			e.dnext = c.defs;
			c.defs = e;
		};
		d = d.next;
	};
};

fn deflookup(c: *cgen, name: str) bool = {
	let e: *defent = c.defs;
	for (e != nil) {
		let dn: str = e.dname;
		if (streq(dn, name)) { return true; };
		e = e.dnext;
	};
	return false;
};

// Returns the rhs init node for a top-level `def`, or nil if `name`
// doesn't name a def. Used by cgdot to inline `.ptr`/`.len` on
// `def NAME: str = "..."` — those aren't laid out in memory.
fn deflookuprhs(c: *cgen, name: str) *node = {
	let e: *defent = c.defs;
	for (e != nil) {
		let dn: str = e.dname;
		if (streq(dn, name)) { return e.drhs; };
		e = e.dnext;
	};
	return nil;
};

// ---- module-private symbol map --------------------------------------
//
// Every non-FFI top-level fn decl lives in its module's namespace —
// cgen mangles the leaf to `<module>.<name>` at the def site (TEXT)
// and at every call/load site, so cross-module same-leaf fns (lib/os
// `read` vs lib/io `read`, both exported) coexist at link time.
// Non-fn decls (let/def/type) stick to the older "non-exported only"
// rule: their export-side namespace is the user-facing data ABI and
// mangling them changes the surface. FFI-bound decls (@symbol) keep
// their explicit C symbol regardless of kind.
//
// Skip rule = {@symbol, main, empty-module}. Do NOT skip on `export`
// for fns. Both stages must match exactly — ww2/ww3/ww4 byte-identity
// depends on it.

type modent = struct {
	mname:  str,	// the bare ident as it appears in source
	module: str,	// the originating module (`// MODULE: foo`)
	mnext:  *modent,
};

fn collectmods(c: *cgen, file: *node) void = {
	c.mods = nil;
	if (file == nil) { return; };
	let d: *node = file.list;
	for (d != nil) {
		// Mirror collectfnrets' shape exactly (plain prepend in one
		// branch). Earlier nested-if/early-return variants tickled a
		// wwstage cgen bug that dropped most prepends.
		if (d.kind == nkind.N_FNDECL) {
			// Fns mangle regardless of export status — covers
			// lib/os.read vs lib/io.read collision.
			if (d.module.len > 0) {
				let isffi: bool = false;
				let a: *node = d.attr;
				for (a != nil) {
					if (a.kind == nkind.N_ATTR) {
						let an: str = a.str;
						if (streq(an, "symbol")) { isffi = true; };
					};
					a = a.next;
				};
				if (!isffi) {
					if (!streq(d.str, "main")) {
						let m: *modent = amalloc(c.a, 48u64): *modent;
						m.mname  = d.str;
						m.module = d.module;
						m.mnext  = c.mods;
						c.mods   = m;
					};
				};
			};
		};
		if (d.kind == nkind.N_DEF) {
			if (d.exported == 0) {
				if (d.module.len > 0) {
					let m: *modent = amalloc(c.a, 48u64): *modent;
					m.mname  = d.str;
					m.module = d.module;
					m.mnext  = c.mods;
					c.mods   = m;
				};
			};
		};
		if (d.kind == nkind.N_TYPEDECL) {
			if (d.exported == 0) {
				if (d.module.len > 0) {
					let m: *modent = amalloc(c.a, 48u64): *modent;
					m.mname  = d.str;
					m.module = d.module;
					m.mnext  = c.mods;
					c.mods   = m;
				};
			};
		};
		if (d.kind == nkind.N_LET) {
			if (d.exported == 0) {
				if (d.module.len > 0) {
					let m: *modent = amalloc(c.a, 48u64): *modent;
					m.mname  = d.str;
					m.module = d.module;
					m.mnext  = c.mods;
					c.mods   = m;
				};
			};
		};
		d = d.next;
	};
};

fn modlookup(c: *cgen, name: str) str = {
	let m: *modent = c.mods;
	for (m != nil) {
		if (streq(m.mname, name)) { return m.module; };
		m = m.mnext;
	};
	let empty: str;
	empty.ptr = nil;
	empty.len = 0;
	return empty;
};

// modlookupforfn — hint-aware lookup for fn names. Walks c.mods
// preferring entries where module matches `hint`; falls back to the
// first leaf-name match when nothing matches the hint (legacy single-
// owner shape, also covers lookups with hint.len==0). Needed because
// multiple modules can now register the same fn leaf — bare `lookup`
// would otherwise grab whichever module was prepended last.
fn modlookupforfn(c: *cgen, name: str, hint: str) str = {
	let m: *modent = c.mods;
	let first: str;
	first.ptr = nil;
	first.len = 0;
	for (m != nil) {
		if (streq(m.mname, name)) {
			if (hint.len > 0 && m.module.len > 0
			    && streq(m.module, hint)) {
				return m.module;
			};
			if (first.len == 0 && first.ptr == nil) {
				first = m.module;
			};
		};
		m = m.mnext;
	};
	return first;
};

// emitsymname — write the asm symbol name for `ident`. Honours, in
// order: FFI mapping (@symbol), module mangling (private decls), bare
// name. Use everywhere a top-level non-fn name is emitted before `(SB)`
// — DATA labels for top-level lets/defs, address-of-let, etc. Fn names
// (CALL/LEAQ-of-fn/TEXT) go through emitfnname so the hint disambiguates
// cross-module same-leaf fn exports.
fn emitsymname(c: *cgen, ident: str) void = {
	let resolved: str = ffiresolve(c, ident);
	if (resolved.ptr != ident.ptr) {
		// FFI hit — emit the mapped linker symbol verbatim.
		os.write(1, resolved.ptr, resolved.len: u64);
		return;
	};
	let mod: str = modlookup(c, ident);
	if (mod.len > 0) {
		os.write(1, mod.ptr, mod.len: u64);
		os.write(1, ".".ptr, 1u64);
	};
	os.write(1, ident.ptr, ident.len: u64);
};

// emitfnname — write the asm symbol name for a fn `ident`, threading
// `hint` (the explicit module from a `mod.fn` use site, or c.curmod
// for bare-IDENT calls) through modlookupforfn. Same FFI override
// semantics as emitsymname; same dot-separator format. Use at every
// CALL / LEAQ-of-fn / TEXT-def site.
fn emitfnname(c: *cgen, ident: str, hint: str) void = {
	let resolved: str = ffiresolve(c, ident);
	if (resolved.ptr != ident.ptr) {
		os.write(1, resolved.ptr, resolved.len: u64);
		return;
	};
	let mod: str = modlookupforfn(c, ident, hint);
	if (mod.len > 0) {
		os.write(1, mod.ptr, mod.len: u64);
		os.write(1, ".".ptr, 1u64);
	};
	os.write(1, ident.ptr, ident.len: u64);
};

// ---- FFI map ---------------------------------------------------------

fn fficollect(c: *cgen, file: *node) void = {
	c.ffis = nil;
	if (file == nil) { return; };
	let d: *node = file.list;
	for (d != nil) {
		if (d.kind == nkind.N_FNDECL) {
			let a: *node = d.attr;
			for (a != nil) {
				if (a.kind == nkind.N_ATTR) {
					let aname: str = a.str;
					if (streq(aname, "symbol")) {
						let symnode: *node = a.list;
						if (symnode != nil) {
							if (symnode.kind == nkind.N_STRLIT) {
								let f: *ffi = amalloc(c.a, 48u64): *ffi;
								f.ident  = d.str;
								f.symbol = symnode.str;
								f.fnext  = c.ffis;
								c.ffis   = f;
							};
						};
					};
				};
				a = a.next;
			};
		};
		d = d.next;
	};
};

fn ffiresolve(c: *cgen, ident: str) str = {
	let f: *ffi = c.ffis;
	for (f != nil) {
		let id: str = f.ident;
		if (streq(id, ident)) { return f.symbol; };
		f = f.fnext;
	};
	return ident;
};

// ---- ABI argreg helpers ---------------------------------------------

fn argregname(i: i32) str = {
	if (i == 0) { return "DI"; };
	if (i == 1) { return "SI"; };
	if (i == 2) { return "DX"; };
	if (i == 3) { return "CX"; };
	if (i == 4) { return "R8"; };
	if (i == 5) { return "R9"; };
	return "?";
};

// fargregname — XMM scalar-float arg registers (SysV: X0..X7).
// Parallel to argregname / sysv_argregs; float args advance their
// own counter so int and float arg slots don't conflict.
export fn fargregname(i: i32) str = {
	if (i == 0) { return "X0"; };
	if (i == 1) { return "X1"; };
	if (i == 2) { return "X2"; };
	if (i == 3) { return "X3"; };
	if (i == 4) { return "X4"; };
	if (i == 5) { return "X5"; };
	if (i == 6) { return "X6"; };
	if (i == 7) { return "X7"; };
	return "?";
};