whileExpr

fn whileExpr(
    parent_gz: *GenZir,
    scope: *Scope,
    ri: ResultInfo,
    node: Ast.Node.Index,
    while_full: Ast.full.While,
    is_statement: bool,
) InnerError!Zir.Inst.Ref {
    const astgen = parent_gz.astgen;
    const tree = astgen.tree;

    const need_rl = astgen.nodes_need_rl.contains(node);
    const block_ri: ResultInfo = if (need_rl) ri else .{
        .rl = switch (ri.rl) {
            .ptr => .{ .ty = (try ri.rl.resultType(parent_gz, node)).? },
            .inferred_ptr => .none,
            else => ri.rl,
        },
        .ctx = ri.ctx,
    };
    // We need to call `rvalue` to write through to the pointer only if we had a
    // result pointer and aren't forwarding it.
    const LocTag = @typeInfo(ResultInfo.Loc).@"union".tag_type.?;
    const need_result_rvalue = @as(LocTag, block_ri.rl) != @as(LocTag, ri.rl);

    if (while_full.label_token) |label_token| {
        try astgen.checkLabelRedefinition(scope, label_token);
    }

    const is_inline = while_full.inline_token != null;
    if (parent_gz.is_comptime and is_inline) {
        try astgen.appendErrorTok(while_full.inline_token.?, "redundant inline keyword in comptime scope", .{});
    }
    const loop_tag: Zir.Inst.Tag = if (is_inline) .block_inline else .loop;
    const loop_block = try parent_gz.makeBlockInst(loop_tag, node);
    try parent_gz.instructions.append(astgen.gpa, loop_block);

    var loop_scope = parent_gz.makeSubBlock(scope);
    loop_scope.is_inline = is_inline;
    loop_scope.setBreakResultInfo(block_ri);
    defer loop_scope.unstack();

    var cond_scope = parent_gz.makeSubBlock(&loop_scope.base);
    defer cond_scope.unstack();

    const payload_is_ref = if (while_full.payload_token) |payload_token|
        tree.tokenTag(payload_token) == .asterisk
    else
        false;

    try emitDbgNode(parent_gz, while_full.ast.cond_expr);
    const cond: struct {
        inst: Zir.Inst.Ref,
        bool_bit: Zir.Inst.Ref,
    } = c: {
        if (while_full.error_token) |_| {
            const cond_ri: ResultInfo = .{ .rl = if (payload_is_ref) .ref else .none };
            const err_union = try fullBodyExpr(&cond_scope, &cond_scope.base, cond_ri, while_full.ast.cond_expr, .normal);
            const tag: Zir.Inst.Tag = if (payload_is_ref) .is_non_err_ptr else .is_non_err;
            break :c .{
                .inst = err_union,
                .bool_bit = try cond_scope.addUnNode(tag, err_union, while_full.ast.cond_expr),
            };
        } else if (while_full.payload_token) |_| {
            const cond_ri: ResultInfo = .{ .rl = if (payload_is_ref) .ref else .none };
            const optional = try fullBodyExpr(&cond_scope, &cond_scope.base, cond_ri, while_full.ast.cond_expr, .normal);
            const tag: Zir.Inst.Tag = if (payload_is_ref) .is_non_null_ptr else .is_non_null;
            break :c .{
                .inst = optional,
                .bool_bit = try cond_scope.addUnNode(tag, optional, while_full.ast.cond_expr),
            };
        } else {
            const cond = try fullBodyExpr(&cond_scope, &cond_scope.base, coerced_bool_ri, while_full.ast.cond_expr, .normal);
            break :c .{
                .inst = cond,
                .bool_bit = cond,
            };
        }
    };

    const condbr_tag: Zir.Inst.Tag = if (is_inline) .condbr_inline else .condbr;
    const condbr = try cond_scope.addCondBr(condbr_tag, node);
    const block_tag: Zir.Inst.Tag = if (is_inline) .block_inline else .block;
    const cond_block = try loop_scope.makeBlockInst(block_tag, node);
    try cond_scope.setBlockBody(cond_block);
    // cond_scope unstacked now, can add new instructions to loop_scope
    try loop_scope.instructions.append(astgen.gpa, cond_block);

    // make scope now but don't stack on parent_gz until loop_scope
    // gets unstacked after cont_expr is emitted and added below
    var then_scope = parent_gz.makeSubBlock(&cond_scope.base);
    then_scope.instructions_top = GenZir.unstacked_top;
    defer then_scope.unstack();

    var dbg_var_name: Zir.NullTerminatedString = .empty;
    var dbg_var_inst: Zir.Inst.Ref = undefined;
    var opt_payload_inst: Zir.Inst.OptionalIndex = .none;
    var payload_val_scope: Scope.LocalVal = undefined;
    const then_sub_scope = s: {
        if (while_full.error_token != null) {
            if (while_full.payload_token) |payload_token| {
                const tag: Zir.Inst.Tag = if (payload_is_ref)
                    .err_union_payload_unsafe_ptr
                else
                    .err_union_payload_unsafe;
                // will add this instruction to then_scope.instructions below
                const payload_inst = try then_scope.makeUnNode(tag, cond.inst, while_full.ast.cond_expr);
                opt_payload_inst = payload_inst.toOptional();
                const ident_token = payload_token + @intFromBool(payload_is_ref);
                const ident_bytes = tree.tokenSlice(ident_token);
                if (mem.eql(u8, "_", ident_bytes)) {
                    if (payload_is_ref) return astgen.failTok(payload_token, "pointer modifier invalid on discard", .{});
                    break :s &then_scope.base;
                }
                const ident_name = try astgen.identAsString(ident_token);
                try astgen.detectLocalShadowing(&then_scope.base, ident_name, ident_token, ident_bytes, .capture);
                payload_val_scope = .{
                    .parent = &then_scope.base,
                    .gen_zir = &then_scope,
                    .name = ident_name,
                    .inst = payload_inst.toRef(),
                    .token_src = ident_token,
                    .id_cat = .capture,
                };
                dbg_var_name = ident_name;
                dbg_var_inst = payload_inst.toRef();
                break :s &payload_val_scope.base;
            } else {
                _ = try then_scope.addUnNode(.ensure_err_union_payload_void, cond.inst, node);
                break :s &then_scope.base;
            }
        } else if (while_full.payload_token) |payload_token| {
            const tag: Zir.Inst.Tag = if (payload_is_ref)
                .optional_payload_unsafe_ptr
            else
                .optional_payload_unsafe;
            // will add this instruction to then_scope.instructions below
            const payload_inst = try then_scope.makeUnNode(tag, cond.inst, while_full.ast.cond_expr);
            opt_payload_inst = payload_inst.toOptional();
            const ident_token = payload_token + @intFromBool(payload_is_ref);
            const ident_name = try astgen.identAsString(ident_token);
            const ident_bytes = tree.tokenSlice(ident_token);
            if (mem.eql(u8, "_", ident_bytes)) {
                if (payload_is_ref) return astgen.failTok(payload_token, "pointer modifier invalid on discard", .{});
                break :s &then_scope.base;
            }
            try astgen.detectLocalShadowing(&then_scope.base, ident_name, ident_token, ident_bytes, .capture);
            payload_val_scope = .{
                .parent = &then_scope.base,
                .gen_zir = &then_scope,
                .name = ident_name,
                .inst = payload_inst.toRef(),
                .token_src = ident_token,
                .id_cat = .capture,
            };
            dbg_var_name = ident_name;
            dbg_var_inst = payload_inst.toRef();
            break :s &payload_val_scope.base;
        } else {
            break :s &then_scope.base;
        }
    };

    var continue_scope = parent_gz.makeSubBlock(then_sub_scope);
    continue_scope.instructions_top = GenZir.unstacked_top;
    defer continue_scope.unstack();
    const continue_block = try then_scope.makeBlockInst(block_tag, node);

    const repeat_tag: Zir.Inst.Tag = if (is_inline) .repeat_inline else .repeat;
    _ = try loop_scope.addNode(repeat_tag, node);

    try loop_scope.setBlockBody(loop_block);
    loop_scope.break_block = loop_block.toOptional();
    loop_scope.continue_block = continue_block.toOptional();
    if (while_full.label_token) |label_token| {
        loop_scope.label = .{
            .token = label_token,
            .block_inst = loop_block,
        };
    }

    // done adding instructions to loop_scope, can now stack then_scope
    then_scope.instructions_top = then_scope.instructions.items.len;

    const then_node = while_full.ast.then_expr;
    if (opt_payload_inst.unwrap()) |payload_inst| {
        try then_scope.instructions.append(astgen.gpa, payload_inst);
    }
    if (dbg_var_name != .empty) try then_scope.addDbgVar(.dbg_var_val, dbg_var_name, dbg_var_inst);
    try then_scope.instructions.append(astgen.gpa, continue_block);
    // This code could be improved to avoid emitting the continue expr when there
    // are no jumps to it. This happens when the last statement of a while body is noreturn
    // and there are no `continue` statements.
    // Tracking issue: https://github.com/ziglang/zig/issues/9185
    if (while_full.ast.cont_expr.unwrap()) |cont_expr| {
        _ = try unusedResultExpr(&then_scope, then_sub_scope, cont_expr);
    }

    continue_scope.instructions_top = continue_scope.instructions.items.len;
    {
        try emitDbgNode(&continue_scope, then_node);
        const unused_result = try fullBodyExpr(&continue_scope, &continue_scope.base, .{ .rl = .none }, then_node, .allow_branch_hint);
        _ = try addEnsureResult(&continue_scope, unused_result, then_node);
    }
    try checkUsed(parent_gz, &then_scope.base, then_sub_scope);
    const break_tag: Zir.Inst.Tag = if (is_inline) .break_inline else .@"break";
    if (!continue_scope.endsWithNoReturn()) {
        astgen.advanceSourceCursor(tree.tokenStart(tree.lastToken(then_node)));
        try emitDbgStmt(parent_gz, .{ astgen.source_line - parent_gz.decl_line, astgen.source_column });
        _ = try parent_gz.add(.{
            .tag = .extended,
            .data = .{ .extended = .{
                .opcode = .dbg_empty_stmt,
                .small = undefined,
                .operand = undefined,
            } },
        });
        _ = try continue_scope.addBreak(break_tag, continue_block, .void_value);
    }
    try continue_scope.setBlockBody(continue_block);
    _ = try then_scope.addBreak(break_tag, cond_block, .void_value);

    var else_scope = parent_gz.makeSubBlock(&cond_scope.base);
    defer else_scope.unstack();

    if (while_full.ast.else_expr.unwrap()) |else_node| {
        const sub_scope = s: {
            if (while_full.error_token) |error_token| {
                const tag: Zir.Inst.Tag = if (payload_is_ref)
                    .err_union_code_ptr
                else
                    .err_union_code;
                const else_payload_inst = try else_scope.addUnNode(tag, cond.inst, while_full.ast.cond_expr);
                const ident_name = try astgen.identAsString(error_token);
                const ident_bytes = tree.tokenSlice(error_token);
                if (mem.eql(u8, ident_bytes, "_"))
                    break :s &else_scope.base;
                try astgen.detectLocalShadowing(&else_scope.base, ident_name, error_token, ident_bytes, .capture);
                payload_val_scope = .{
                    .parent = &else_scope.base,
                    .gen_zir = &else_scope,
                    .name = ident_name,
                    .inst = else_payload_inst,
                    .token_src = error_token,
                    .id_cat = .capture,
                };
                try else_scope.addDbgVar(.dbg_var_val, ident_name, else_payload_inst);
                break :s &payload_val_scope.base;
            } else {
                break :s &else_scope.base;
            }
        };
        // Remove the continue block and break block so that `continue` and `break`
        // control flow apply to outer loops; not this one.
        loop_scope.continue_block = .none;
        loop_scope.break_block = .none;
        const else_result = try fullBodyExpr(&else_scope, sub_scope, loop_scope.break_result_info, else_node, .allow_branch_hint);
        if (is_statement) {
            _ = try addEnsureResult(&else_scope, else_result, else_node);
        }

        try checkUsed(parent_gz, &else_scope.base, sub_scope);
        if (!else_scope.endsWithNoReturn()) {
            _ = try else_scope.addBreakWithSrcNode(break_tag, loop_block, else_result, else_node);
        }
    } else {
        const result = try rvalue(&else_scope, ri, .void_value, node);
        _ = try else_scope.addBreak(break_tag, loop_block, result);
    }

    if (loop_scope.label) |some| {
        if (!some.used) {
            try astgen.appendErrorTok(some.token, "unused while loop label", .{});
        }
    }

    try setCondBrPayload(condbr, cond.bool_bit, &then_scope, &else_scope);

    const result = if (need_result_rvalue)
        try rvalue(parent_gz, ri, loop_block.toRef(), node)
    else
        loop_block.toRef();

    if (is_statement) {
        _ = try parent_gz.addUnNode(.ensure_result_used, result, node);
    }

    return result;
}