// selfhost/cmd/wcc/cgendecl.ww — split out of cgen.ww.
//
// Houses the top-level emission glue:
//   - cgfnparams: parameter spilling per SysV
//   - cgfn:       fn body emit (TEXT/SUBQ patched after body), prologue
//                 deferred via cgen.ww's cgoutstate so the frame size
//                 reflects every emit-time localadd (#15/#26c)
//   - cgfile:     file-level entry (the exported driver)
//
// Bundler pulls this in transitively via cgen.ww; consumers don't
// need to `use cgendecl;` directly.

package wcc;

import os;
import ast;
import tok;
import typ;
import sym;
import strconv;


// ---- function-level cgen ---------------------------------------------

fn cgfnparams(c: *cgen, params: *node) void = {
	let p: *node = params;
	// sret (#23): RDI is consumed by the hidden dest pointer
	// (already spilled to @sretarg by cgfn); the first user param
	// lands in SI.
	let idx: i32 = 0;
	if (localfind(c, "@sretarg") != 0) { idx = 1; };
	let fidx: i32 = 0;
	// Cursor for args that overflow the SysV reg windows. Each
	// stack-passed arg lives at 16+8*k(BP) — no spill, the local
	// is registered with a *positive* offset pointing into the
	// caller's frame. Mirrors C cgen's cg_stack_arg_cursor.
	let stkcursor: i32 = 0;
	for (p != nil) {
		if (p.kind == nkind.N_PARAM) {
			let nm: str = p.str;
			// Hare-style variadic `T...`: callee receives a []T
			// slice (3 register words / 24B). p.lhs is already
			// the []T wrap installed by check.ww installparams
			// (mirrors cstage check.c:455 tp->type promotion), so
			// we consume it directly — re-wrapping via slicewrap
			// would yield [][]T.
			if (p.op == tkind.TK_ELLIPSIS) {
				let tn: *node = p.lhs;
				if (idx + 3 <= 6) {
					let off: i32 = localadd(c, nm, tyslicesize(): i32, tn);
					emitline("\tMOVQ\t");
					emitline(argregname(idx));
					emitline(", ");
					emitoff(off: i64);
					emitline("(BP)\n");
					idx += 1;
					emitline("\tMOVQ\t");
					emitline(argregname(idx));
					emitline(", ");
					emitoff((off + 8): i64);
					emitline("(BP)\n");
					idx += 1;
					emitline("\tMOVQ\t");
					emitline(argregname(idx));
					emitline(", ");
					emitoff((off + 16): i64);
					emitline("(BP)\n");
					idx += 1;
				} else { if (idx < 6) {
					// Partial-fit stitch — variadic `T...` is a slice
					// at the ABI boundary (the call site synthesises a
					// 24B descriptor and pushes ptr/len/cap), so this
					// mirrors the slice branch at cgendecl.ww:518.
					let off: i32 = localadd(c, nm, tyslicesize(): i32, tn);
					let regs_left: i32 = 6 - idx;
					let w: i32 = 0;
					for (w < regs_left) {
						emitline("\tMOVQ\t");
						emitline(argregname(idx));
						emitline(", ");
						emitoff((off + w*8): i64);
						emitline("(BP)\n");
						idx += 1;
						w += 1;
					};
					for (w < 3) {
						emitline("\tMOVQ\t");
						emitoff((16 + stkcursor*8): i64);
						emitline("(BP), AX\n");
						emitline("\tMOVQ\tAX, ");
						emitoff((off + w*8): i64);
						emitline("(BP)\n");
						stkcursor += 1;
						w += 1;
					};
				} else {
					localaddstack(c, nm, tn, 16 + stkcursor*8);
					stkcursor += 3;
				};};
				p = p.next;
				continue;
			};
			if (isfloattype(c, p.lhs)) {
				// Float param: SysV uses the XMM stream
				// (X0..X7). 8B (f64) or 4B (f32) slot.
				let fsz: i32 = 8;
				if (isf32type(c, p.lhs)) { fsz = 4; };
				if (fidx < 8) {
					let off: i32 = localadd(c, nm, fsz, p.lhs);
					let mov: str = "MOVSD";
					if (fsz == 4) { mov = "MOVSS"; };
					emitline("\t");
					emitline(mov);
					emitline("\t");
					emitline(fargregname(fidx));
					emitline(", ");
					emitoff(off: i64);
					emitline("(BP)\n");
					fidx += 1;
				} else {
					localaddstack(c, nm, p.lhs, 16 + stkcursor*8);
					stkcursor += 1;
				};
				p = p.next;
				continue;
			};
			if (istaggedtype(c, p.lhs)) {
				let slot: i32 = slotsize(c, p.lhs);
				let nw: i32 = slot / 8;
				if (idx + nw <= 6) {
					let off: i32 = localadd(c, nm, slot, p.lhs);
					let w: i32 = 0;
					for (w < nw) {
						emitline("\tMOVQ\t");
						emitline(argregname(idx));
						emitline(", ");
						emitoff((off + w*8): i64);
						emitline("(BP)\n");
						idx += 1;
						w += 1;
					};
				} else { if (idx < 6 && nw > 1) {
					// Partial fit: fill remaining regs, then read
					// the tail from positive BP offsets. Mirrors
					// the caller's greedy reg fill in pushargsrev.
					let off: i32 = localadd(c, nm, slot, p.lhs);
					let regs_left: i32 = 6 - idx;
					let w: i32 = 0;
					for (w < regs_left) {
						emitline("\tMOVQ\t");
						emitline(argregname(idx));
						emitline(", ");
						emitoff((off + w*8): i64);
						emitline("(BP)\n");
						idx += 1;
						w += 1;
					};
					for (w < nw) {
						emitline("\tMOVQ\t");
						emitoff((16 + stkcursor*8): i64);
						emitline("(BP), AX\n");
						emitline("\tMOVQ\tAX, ");
						emitoff((off + w*8): i64);
						emitline("(BP)\n");
						stkcursor += 1;
						w += 1;
					};
				} else {
					localaddstack(c, nm, p.lhs, 16 + stkcursor*8);
					stkcursor += nw;
				};};
			} else { if (isslicetype(c, p.lhs)) {
				if (idx + 3 <= 6) {
					let off: i32 = localadd(c, nm, tyslicesize(): i32, p.lhs);
					emitline("\tMOVQ\t");
					emitline(argregname(idx));
					emitline(", ");
					emitoff(off: i64);
					emitline("(BP)\n");
					idx += 1;
					emitline("\tMOVQ\t");
					emitline(argregname(idx));
					emitline(", ");
					emitoff((off + 8): i64);
					emitline("(BP)\n");
					idx += 1;
					emitline("\tMOVQ\t");
					emitline(argregname(idx));
					emitline(", ");
					emitoff((off + 16): i64);
					emitline("(BP)\n");
					idx += 1;
				} else { if (idx < 6) {
					// Partial-fit stitch — mirrors tagged at lines
					// 440-469. Caller's pushargsrev greedy-fills the
					// remaining argregs (ptr,len,cap order), the tail
					// spills to +16+stkcursor*8(BP).
					let off: i32 = localadd(c, nm, tyslicesize(): i32, p.lhs);
					let regs_left: i32 = 6 - idx;
					let w: i32 = 0;
					for (w < regs_left) {
						emitline("\tMOVQ\t");
						emitline(argregname(idx));
						emitline(", ");
						emitoff((off + w*8): i64);
						emitline("(BP)\n");
						idx += 1;
						w += 1;
					};
					for (w < 3) {
						emitline("\tMOVQ\t");
						emitoff((16 + stkcursor*8): i64);
						emitline("(BP), AX\n");
						emitline("\tMOVQ\tAX, ");
						emitoff((off + w*8): i64);
						emitline("(BP)\n");
						stkcursor += 1;
						w += 1;
					};
				} else {
					localaddstack(c, nm, p.lhs, 16 + stkcursor*8);
					stkcursor += 3;
				};};
			} else { if (isstrtype(c, p.lhs)) {
				if (idx + 3 <= 6) {
					// str IS []u8: 3-word param (ptr,len,cap), same as
					// the slice arm above (#1/Phase 3). #60: route slot
					// width through the primtypesize SSoT so #1's ty_str
					// bump propagates here.
					let off: i32 = localadd(c, nm, primtypesize("str"): i32, p.lhs);
					emitline("\tMOVQ\t");
					emitline(argregname(idx));
					emitline(", ");
					emitoff(off: i64);
					emitline("(BP)\n");
					idx += 1;
					emitline("\tMOVQ\t");
					emitline(argregname(idx));
					emitline(", ");
					emitoff((off + 8): i64);
					emitline("(BP)\n");
					idx += 1;
					emitline("\tMOVQ\t");
					emitline(argregname(idx));
					emitline(", ");
					emitoff((off + 16): i64);
					emitline("(BP)\n");
					idx += 1;
				} else { if (idx < 6) {
					// Partial-fit stitch — mirrors the slice arm above.
					// #60: same SSoT routing as the regs-fit arm above.
					let off: i32 = localadd(c, nm, primtypesize("str"): i32, p.lhs);
					let regs_left: i32 = 6 - idx;
					let w: i32 = 0;
					for (w < regs_left) {
						emitline("\tMOVQ\t");
						emitline(argregname(idx));
						emitline(", ");
						emitoff((off + w*8): i64);
						emitline("(BP)\n");
						idx += 1;
						w += 1;
					};
					for (w < 3) {
						emitline("\tMOVQ\t");
						emitoff((16 + stkcursor*8): i64);
						emitline("(BP), AX\n");
						emitline("\tMOVQ\tAX, ");
						emitoff((off + w*8): i64);
						emitline("(BP)\n");
						stkcursor += 1;
						w += 1;
					};
				} else {
					localaddstack(c, nm, p.lhs, 16 + stkcursor*8);
					stkcursor += 3;
				};};
			} else { let stsz: i32 = structparamsize(c, p.lhs);
				if (stsz > 0) {
					// User-defined by-value struct ≤ 16B: 1 or 2
					// integer eightbytes. Mirrors cstage's
					// `struct_eb = (pu->size > 8) ? 2 : 1` and the
					// matching reg/stack/stitch arms in cgen.c cgfn.
					let nw: i32 = 1;
					if (stsz > 8) { nw = 2; };
					if (idx + nw <= 6) {
						let off: i32 = localadd(c, nm, stsz, p.lhs);
						let w: i32 = 0;
						for (w < nw) {
							emitline("\tMOVQ\t");
							emitline(argregname(idx));
							emitline(", ");
							emitoff((off + w*8): i64);
							emitline("(BP)\n");
							idx += 1;
							w += 1;
						};
					} else { if (idx < 6 && nw > 1) {
						let off: i32 = localadd(c, nm, stsz, p.lhs);
						let regs_left: i32 = 6 - idx;
						let w: i32 = 0;
						for (w < regs_left) {
							emitline("\tMOVQ\t");
							emitline(argregname(idx));
							emitline(", ");
							emitoff((off + w*8): i64);
							emitline("(BP)\n");
							idx += 1;
							w += 1;
						};
						for (w < nw) {
							emitline("\tMOVQ\t");
							emitoff((16 + stkcursor*8): i64);
							emitline("(BP), AX\n");
							emitline("\tMOVQ\tAX, ");
							emitoff((off + w*8): i64);
							emitline("(BP)\n");
							stkcursor += 1;
							w += 1;
						};
					} else {
						localaddstack(c, nm, p.lhs, 16 + stkcursor*8);
						stkcursor += nw;
					};};
				} else {
					if (idx < 6) {
						let off: i32 = localadd(c, nm, 8, p.lhs);
						emitline("\tMOVQ\t");
						emitline(argregname(idx));
						emitline(", ");
						emitoff(off: i64);
						emitline("(BP)\n");
						idx += 1;
					} else {
						localaddstack(c, nm, p.lhs, 16 + stkcursor*8);
						stkcursor += 1;
					};
				};
			};};};
		};
		p = p.next;
	};
};

fn cgfn(c: *cgen, fn_: *node) void = {
	cgeninit(c);
	c.fnname = fn_.str;
	c.curmod = fn_.nmod;
	c.fnret  = fn_.lhs;

	// sret callee (#23): return type is plain TY_STRUCT > 24B.
	// Reserve 8B for @sretarg (holds the saved hidden RDI dest
	// pointer); cgfnparams skips DI for user args, cgreturn writes
	// through *(@sretarg) and returns @sretarg in RAX.
	let sret_callee: bool = sretretsize(c, c.fnret) > 0;

	// Capture the body into cgoutstate while c.frame grows under
	// emit-time localadd calls (#15/#26c — wwstage dropped its
	// scanlocals pre-pass to align DOWN with cstage's first-use
	// pattern). The prologue (TEXT label, PUSHQ/MOVQ/SUBQ) emits
	// after the body finishes so the frame size reflects every
	// localadd. Mirrors cstage cmd/w6c/cgen.c cgfn which builds
	// `subsp`/`text` Progs up front and patches their `from.offset`
	// at the end via txt_emit.
	cgout_enable();

	if (sret_callee) {
		let saoff: i32 = localadd(c, "@sretarg", 8, nil);
		emitline("\tMOVQ\tDI, ");
		emitoff(saoff: i64);
		emitline("(BP)\n");
	};

	cgfnparams(c, fn_.list);
	c.lastwasreturn = 0;
	// Iterate the fn body's statements directly rather than dispatching
	// the outermost N_BLOCK through cgstmt — cgblock now save/restores
	// c.locals to scope inner shadows (post-#27), but the function body
	// is not "an inner block": defers (queued during the body) and the
	// implicit-return epilogue both call cgexpr after this loop and
	// resolve identifiers via localfind, so the body's locals must
	// still be in c.locals when we get there.
	if (fn_.body != nil) {
		if (fn_.body.kind == nkind.N_BLOCK) {
			let s: *node = fn_.body.list;
			for (s != nil) {
				cgstmt(c, s);
				s = s.next;
			};
		} else {
			cgstmt(c, fn_.body);
		};
	};

	if (c.lastwasreturn == 0) {
		// Run any registered defers in LIFO order before the
		// implicit return.
		rundefers(c);
		// Zero AX before the fall-through return — matches cstage,
		// which always emits this so void-returning fns don't leak
		// a stale callee value to their caller.
		emitline("\tMOVQ\t$0, AX\n");
		emitline("\tMOVQ\tBP, SP\n");
		emitline("\tPOPQ\tBP\n");
		emitline("\tRET\n");
	};

	cgout_disable();

	let frame: i32 = c.frame;
	if ((frame & 15) != 0) { frame = (frame + 15) & ~15; };

	// Emit the TEXT label via emitfnname so the def site picks up the
	// same skip rule (FFI / `main` / empty-module) and the same module
	// hint (this fn's own module) that the call sites use.
	emitline("TEXT ");
	emitfnname(c, fn_.str, fn_.nmod);
	emitline(",$");
	emitint(frame: i64);
	emitline("\n");

	emitline("\tPUSHQ\tBP\n");
	emitline("\tMOVQ\tSP, BP\n");
	emitline("\tSUBQ\t$");
	emitint(frame: i64);
	emitline(", SP\n");

	cgout_flush();
};

// ---- file-level entry ------------------------------------------------

export fn cgfile(c: *cgen, file: *node) void = {
	if (file == nil) { return; };
	c.strlits = nil;
	c.strlitseq = 0;
	collectaliases(c, file);
	// Enums must register before structs — fieldsize on a tkind-typed
	// field needs the enum's storage size, otherwise it falls back to
	// 8 (wrong load width).
	collectenums(c, file);
	collectstructs(c, file);
	collectdefs(c, file);
	collectfnrets(c, file);
	fficollect(c, file);
	collectmods(c, file);
	collectlets(c, file);
	let d: *node = file.list;
	for (d != nil) {
		if (d.kind == nkind.N_FNDECL) {
			if (d.body != nil) {
				cgfn(c, d);
			};
		};
		d = d.next;
	};
	letpreintern(c, file);
	emitdatasection(c);
	emitdefconstants(c, file);
	emitletdataw(c, file);
};