path: root/compiler/rustc_builtin_macros/src/asm.rs

use rustc_ast as ast;
use rustc_ast::ptr::P;
use rustc_ast::token::{self, Delimiter};
use rustc_ast::tokenstream::TokenStream;
use rustc_data_structures::fx::{FxHashMap, FxIndexMap};
use rustc_errors::PResult;
use rustc_expand::base::{self, *};
use rustc_index::bit_set::GrowableBitSet;
use rustc_parse::parser::Parser;
use rustc_parse_format as parse;
use rustc_session::lint;
use rustc_session::parse::ParseSess;
use rustc_span::symbol::Ident;
use rustc_span::symbol::{kw, sym, Symbol};
use rustc_span::{InnerSpan, Span};
use rustc_target::asm::InlineAsmArch;
use smallvec::smallvec;

use crate::errors;

pub struct AsmArgs {
    pub templates: Vec<P<ast::Expr>>,
    pub operands: Vec<(ast::InlineAsmOperand, Span)>,
    named_args: FxIndexMap<Symbol, usize>,
    reg_args: GrowableBitSet<usize>,
    pub clobber_abis: Vec<(Symbol, Span)>,
    options: ast::InlineAsmOptions,
    pub options_spans: Vec<Span>,
}

fn parse_args<'a>(
    ecx: &mut ExtCtxt<'a>,
    sp: Span,
    tts: TokenStream,
    is_global_asm: bool,
) -> PResult<'a, AsmArgs> {
    let mut p = ecx.new_parser_from_tts(tts);
    let sess = &ecx.sess.parse_sess;
    parse_asm_args(&mut p, sess, sp, is_global_asm)
}

// Primarily public for rustfmt consumption.
// Internal consumers should continue to leverage `expand_asm`/`expand__global_asm`
pub fn parse_asm_args<'a>(
    p: &mut Parser<'a>,
    sess: &'a ParseSess,
    sp: Span,
    is_global_asm: bool,
) -> PResult<'a, AsmArgs> {
    let dcx = &sess.dcx;

    if p.token == token::Eof {
        return Err(dcx.create_err(errors::AsmRequiresTemplate { span: sp }));
    }

    let first_template = p.parse_expr()?;
    let mut args = AsmArgs {
        templates: vec![first_template],
        operands: vec![],
        named_args: Default::default(),
        reg_args: Default::default(),
        clobber_abis: Vec::new(),
        options: ast::InlineAsmOptions::empty(),
        options_spans: vec![],
    };

    let mut allow_templates = true;
    while p.token != token::Eof {
        if !p.eat(&token::Comma) {
            if allow_templates {
                // After a template string, we always expect *only* a comma...
                return Err(dcx.create_err(errors::AsmExpectedComma { span: p.token.span }));
            } else {
                // ...after that delegate to `expect` to also include the other expected tokens.
                return Err(p.expect(&token::Comma).err().unwrap());
            }
        }
        if p.token == token::Eof {
            break;
        } // accept trailing commas

        // Parse clobber_abi
        if p.eat_keyword(sym::clobber_abi) {
            parse_clobber_abi(p, &mut args)?;
            allow_templates = false;
            continue;
        }

        // Parse options
        if p.eat_keyword(sym::options) {
            parse_options(p, &mut args, is_global_asm)?;
            allow_templates = false;
            continue;
        }

        let span_start = p.token.span;

        // Parse operand names
        let name = if p.token.is_ident() && p.look_ahead(1, |t| *t == token::Eq) {
            let (ident, _) = p.token.ident().unwrap();
            p.bump();
            p.expect(&token::Eq)?;
            allow_templates = false;
            Some(ident.name)
        } else {
            None
        };

        let mut explicit_reg = false;
        let op = if !is_global_asm && p.eat_keyword(kw::In) {
            let reg = parse_reg(p, &mut explicit_reg)?;
            if p.eat_keyword(kw::Underscore) {
                let err = dcx.create_err(errors::AsmUnderscoreInput { span: p.token.span });
                return Err(err);
            }
            let expr = p.parse_expr()?;
            ast::InlineAsmOperand::In { reg, expr }
        } else if !is_global_asm && p.eat_keyword(sym::out) {
            let reg = parse_reg(p, &mut explicit_reg)?;
            let expr = if p.eat_keyword(kw::Underscore) { None } else { Some(p.parse_expr()?) };
            ast::InlineAsmOperand::Out { reg, expr, late: false }
        } else if !is_global_asm && p.eat_keyword(sym::lateout) {
            let reg = parse_reg(p, &mut explicit_reg)?;
            let expr = if p.eat_keyword(kw::Underscore) { None } else { Some(p.parse_expr()?) };
            ast::InlineAsmOperand::Out { reg, expr, late: true }
        } else if !is_global_asm && p.eat_keyword(sym::inout) {
            let reg = parse_reg(p, &mut explicit_reg)?;
            if p.eat_keyword(kw::Underscore) {
                let err = dcx.create_err(errors::AsmUnderscoreInput { span: p.token.span });
                return Err(err);
            }
            let expr = p.parse_expr()?;
            if p.eat(&token::FatArrow) {
                let out_expr =
                    if p.eat_keyword(kw::Underscore) { None } else { Some(p.parse_expr()?) };
                ast::InlineAsmOperand::SplitInOut { reg, in_expr: expr, out_expr, late: false }
            } else {
                ast::InlineAsmOperand::InOut { reg, expr, late: false }
            }
        } else if !is_global_asm && p.eat_keyword(sym::inlateout) {
            let reg = parse_reg(p, &mut explicit_reg)?;
            if p.eat_keyword(kw::Underscore) {
                let err = dcx.create_err(errors::AsmUnderscoreInput { span: p.token.span });
                return Err(err);
            }
            let expr = p.parse_expr()?;
            if p.eat(&token::FatArrow) {
                let out_expr =
                    if p.eat_keyword(kw::Underscore) { None } else { Some(p.parse_expr()?) };
                ast::InlineAsmOperand::SplitInOut { reg, in_expr: expr, out_expr, late: true }
            } else {
                ast::InlineAsmOperand::InOut { reg, expr, late: true }
            }
        } else if p.eat_keyword(kw::Const) {
            let anon_const = p.parse_expr_anon_const()?;
            ast::InlineAsmOperand::Const { anon_const }
        } else if p.eat_keyword(sym::sym) {
            let expr = p.parse_expr()?;
            let ast::ExprKind::Path(qself, path) = &expr.kind else {
                let err = dcx.create_err(errors::AsmSymNoPath { span: expr.span });
                return Err(err);
            };
            let sym = ast::InlineAsmSym {
                id: ast::DUMMY_NODE_ID,
                qself: qself.clone(),
                path: path.clone(),
            };
            ast::InlineAsmOperand::Sym { sym }
        } else if allow_templates {
            let template = p.parse_expr()?;
            // If it can't possibly expand to a string, provide diagnostics here to include other
            // things it could have been.
            match template.kind {
                ast::ExprKind::Lit(token_lit)
                    if matches!(
                        token_lit.kind,
                        token::LitKind::Str | token::LitKind::StrRaw(_)
                    ) => {}
                ast::ExprKind::MacCall(..) => {}
                _ => {
                    let err = dcx.create_err(errors::AsmExpectedOther {
                        span: template.span,
                        is_global_asm,
                    });
                    return Err(err);
                }
            }
            args.templates.push(template);
            continue;
        } else {
            return p.unexpected();
        };

        allow_templates = false;
        let span = span_start.to(p.prev_token.span);
        let slot = args.operands.len();
        args.operands.push((op, span));

        // Validate the order of named, positional & explicit register operands and
        // clobber_abi/options. We do this at the end once we have the full span
        // of the argument available.
        if explicit_reg {
            if name.is_some() {
                dcx.emit_err(errors::AsmExplicitRegisterName { span });
            }
            args.reg_args.insert(slot);
        } else if let Some(name) = name {
            if let Some(&prev) = args.named_args.get(&name) {
                dcx.emit_err(errors::AsmDuplicateArg { span, name, prev: args.operands[prev].1 });
                continue;
            }
            args.named_args.insert(name, slot);
        } else {
            if !args.named_args.is_empty() || !args.reg_args.is_empty() {
                let named = args.named_args.values().map(|p| args.operands[*p].1).collect();
                let explicit = args.reg_args.iter().map(|p| args.operands[p].1).collect();

                dcx.emit_err(errors::AsmPositionalAfter { span, named, explicit });
            }
        }
    }

    if args.options.contains(ast::InlineAsmOptions::NOMEM)
        && args.options.contains(ast::InlineAsmOptions::READONLY)
    {
        let spans = args.options_spans.clone();
        dcx.emit_err(errors::AsmMutuallyExclusive { spans, opt1: "nomem", opt2: "readonly" });
    }
    if args.options.contains(ast::InlineAsmOptions::PURE)
        && args.options.contains(ast::InlineAsmOptions::NORETURN)
    {
        let spans = args.options_spans.clone();
        dcx.emit_err(errors::AsmMutuallyExclusive { spans, opt1: "pure", opt2: "noreturn" });
    }
    if args.options.contains(ast::InlineAsmOptions::PURE)
        && !args.options.intersects(ast::InlineAsmOptions::NOMEM | ast::InlineAsmOptions::READONLY)
    {
        let spans = args.options_spans.clone();
        dcx.emit_err(errors::AsmPureCombine { spans });
    }

    let mut have_real_output = false;
    let mut outputs_sp = vec![];
    let mut regclass_outputs = vec![];
    for (op, op_sp) in &args.operands {
        match op {
            ast::InlineAsmOperand::Out { reg, expr, .. }
            | ast::InlineAsmOperand::SplitInOut { reg, out_expr: expr, .. } => {
                outputs_sp.push(*op_sp);
                have_real_output |= expr.is_some();
                if let ast::InlineAsmRegOrRegClass::RegClass(_) = reg {
                    regclass_outputs.push(*op_sp);
                }
            }
            ast::InlineAsmOperand::InOut { reg, .. } => {
                outputs_sp.push(*op_sp);
                have_real_output = true;
                if let ast::InlineAsmRegOrRegClass::RegClass(_) = reg {
                    regclass_outputs.push(*op_sp);
                }
            }
            _ => {}
        }
    }
    if args.options.contains(ast::InlineAsmOptions::PURE) && !have_real_output {
        dcx.emit_err(errors::AsmPureNoOutput { spans: args.options_spans.clone() });
    }
    if args.options.contains(ast::InlineAsmOptions::NORETURN) && !outputs_sp.is_empty() {
        let err = dcx.create_err(errors::AsmNoReturn { outputs_sp });
        // Bail out now since this is likely to confuse MIR
        return Err(err);
    }

    if args.clobber_abis.len() > 0 {
        if is_global_asm {
            let err = dcx.create_err(errors::GlobalAsmClobberAbi {
                spans: args.clobber_abis.iter().map(|(_, span)| *span).collect(),
            });

            // Bail out now since this is likely to confuse later stages
            return Err(err);
        }
        if !regclass_outputs.is_empty() {
            dcx.emit_err(errors::AsmClobberNoReg {
                spans: regclass_outputs,
                clobbers: args.clobber_abis.iter().map(|(_, span)| *span).collect(),
            });
        }
    }

    Ok(args)
}

/// Report a duplicate option error.
///
/// This function must be called immediately after the option token is parsed.
/// Otherwise, the suggestion will be incorrect.
fn err_duplicate_option(p: &mut Parser<'_>, symbol: Symbol, span: Span) {
    // Tool-only output
    let full_span = if p.token.kind == token::Comma { span.to(p.token.span) } else { span };
    p.sess.dcx.emit_err(errors::AsmOptAlreadyprovided { span, symbol, full_span });
}

/// Try to set the provided option in the provided `AsmArgs`.
/// If it is already set, report a duplicate option error.
///
/// This function must be called immediately after the option token is parsed.
/// Otherwise, the error will not point to the correct spot.
fn try_set_option<'a>(
    p: &mut Parser<'a>,
    args: &mut AsmArgs,
    symbol: Symbol,
    option: ast::InlineAsmOptions,
) {
    if !args.options.contains(option) {
        args.options |= option;
    } else {
        err_duplicate_option(p, symbol, p.prev_token.span);
    }
}

fn parse_options<'a>(
    p: &mut Parser<'a>,
    args: &mut AsmArgs,
    is_global_asm: bool,
) -> PResult<'a, ()> {
    let span_start = p.prev_token.span;

    p.expect(&token::OpenDelim(Delimiter::Parenthesis))?;

    while !p.eat(&token::CloseDelim(Delimiter::Parenthesis)) {
        if !is_global_asm && p.eat_keyword(sym::pure) {
            try_set_option(p, args, sym::pure, ast::InlineAsmOptions::PURE);
        } else if !is_global_asm && p.eat_keyword(sym::nomem) {
            try_set_option(p, args, sym::nomem, ast::InlineAsmOptions::NOMEM);
        } else if !is_global_asm && p.eat_keyword(sym::readonly) {
            try_set_option(p, args, sym::readonly, ast::InlineAsmOptions::READONLY);
        } else if !is_global_asm && p.eat_keyword(sym::preserves_flags) {
            try_set_option(p, args, sym::preserves_flags, ast::InlineAsmOptions::PRESERVES_FLAGS);
        } else if !is_global_asm && p.eat_keyword(sym::noreturn) {
            try_set_option(p, args, sym::noreturn, ast::InlineAsmOptions::NORETURN);
        } else if !is_global_asm && p.eat_keyword(sym::nostack) {
            try_set_option(p, args, sym::nostack, ast::InlineAsmOptions::NOSTACK);
        } else if !is_global_asm && p.eat_keyword(sym::may_unwind) {
            try_set_option(p, args, kw::Raw, ast::InlineAsmOptions::MAY_UNWIND);
        } else if p.eat_keyword(sym::att_syntax) {
            try_set_option(p, args, sym::att_syntax, ast::InlineAsmOptions::ATT_SYNTAX);
        } else if p.eat_keyword(kw::Raw) {
            try_set_option(p, args, kw::Raw, ast::InlineAsmOptions::RAW);
        } else {
            return p.unexpected();
        }

        // Allow trailing commas
        if p.eat(&token::CloseDelim(Delimiter::Parenthesis)) {
            break;
        }
        p.expect(&token::Comma)?;
    }

    let new_span = span_start.to(p.prev_token.span);
    args.options_spans.push(new_span);

    Ok(())
}

fn parse_clobber_abi<'a>(p: &mut Parser<'a>, args: &mut AsmArgs) -> PResult<'a, ()> {
    let span_start = p.prev_token.span;

    p.expect(&token::OpenDelim(Delimiter::Parenthesis))?;

    if p.eat(&token::CloseDelim(Delimiter::Parenthesis)) {
        return Err(p.sess.dcx.create_err(errors::NonABI { span: p.token.span }));
    }

    let mut new_abis = Vec::new();
    while !p.eat(&token::CloseDelim(Delimiter::Parenthesis)) {
        match p.parse_str_lit() {
            Ok(str_lit) => {
                new_abis.push((str_lit.symbol_unescaped, str_lit.span));
            }
            Err(opt_lit) => {
                let span = opt_lit.map_or(p.token.span, |lit| lit.span);
                let mut err = p.sess.dcx.struct_span_err(span, "expected string literal");
                err.span_label(span, "not a string literal");
                return Err(err);
            }
        };

        // Allow trailing commas
        if p.eat(&token::CloseDelim(Delimiter::Parenthesis)) {
            break;
        }
        p.expect(&token::Comma)?;
    }

    let full_span = span_start.to(p.prev_token.span);

    match &new_abis[..] {
        // should have errored above during parsing
        [] => unreachable!(),
        [(abi, _span)] => args.clobber_abis.push((*abi, full_span)),
        abis => {
            for (abi, span) in abis {
                args.clobber_abis.push((*abi, *span));
            }
        }
    }

    Ok(())
}

fn parse_reg<'a>(
    p: &mut Parser<'a>,
    explicit_reg: &mut bool,
) -> PResult<'a, ast::InlineAsmRegOrRegClass> {
    p.expect(&token::OpenDelim(Delimiter::Parenthesis))?;
    let result = match p.token.uninterpolate().kind {
        token::Ident(name, false) => ast::InlineAsmRegOrRegClass::RegClass(name),
        token::Literal(token::Lit { kind: token::LitKind::Str, symbol, suffix: _ }) => {
            *explicit_reg = true;
            ast::InlineAsmRegOrRegClass::Reg(symbol)
        }
        _ => {
            return Err(p.sess.create_err(errors::ExpectedRegisterClassOrExplicitRegister {
                span: p.token.span,
            }));
        }
    };
    p.bump();
    p.expect(&token::CloseDelim(Delimiter::Parenthesis))?;
    Ok(result)
}

fn expand_preparsed_asm(ecx: &mut ExtCtxt<'_>, args: AsmArgs) -> Option<ast::InlineAsm> {
    let mut template = vec![];
    // Register operands are implicitly used since they are not allowed to be
    // referenced in the template string.
    let mut used = vec![false; args.operands.len()];
    for pos in args.reg_args.iter() {
        used[pos] = true;
    }
    let named_pos: FxHashMap<usize, Symbol> =
        args.named_args.iter().map(|(&sym, &idx)| (idx, sym)).collect();
    let mut line_spans = Vec::with_capacity(args.templates.len());
    let mut curarg = 0;

    let mut template_strs = Vec::with_capacity(args.templates.len());

    for (i, template_expr) in args.templates.into_iter().enumerate() {
        if i != 0 {
            template.push(ast::InlineAsmTemplatePiece::String("\n".to_string()));
        }

        let msg = "asm template must be a string literal";
        let template_sp = template_expr.span;
        let (template_str, template_style, template_span) =
            match expr_to_spanned_string(ecx, template_expr, msg) {
                Ok(template_part) => template_part,
                Err(err) => {
                    if let Some((mut err, _)) = err {
                        err.emit();
                    }
                    return None;
                }
            };

        let str_style = match template_style {
            ast::StrStyle::Cooked => None,
            ast::StrStyle::Raw(raw) => Some(raw as usize),
        };

        let template_snippet = ecx.source_map().span_to_snippet(template_sp).ok();
        template_strs.push((
            template_str,
            template_snippet.as_deref().map(Symbol::intern),
            template_sp,
        ));
        let template_str = template_str.as_str();

        if let Some(InlineAsmArch::X86 | InlineAsmArch::X86_64) = ecx.sess.asm_arch {
            let find_span = |needle: &str| -> Span {
                if let Some(snippet) = &template_snippet {
                    if let Some(pos) = snippet.find(needle) {
                        let end = pos
                            + snippet[pos..]
                                .find(|c| matches!(c, '\n' | ';' | '\\' | '"'))
                                .unwrap_or(snippet[pos..].len() - 1);
                        let inner = InnerSpan::new(pos, end);
                        return template_sp.from_inner(inner);
                    }
                }
                template_sp
            };

            if template_str.contains(".intel_syntax") {
                ecx.parse_sess().buffer_lint(
                    lint::builtin::BAD_ASM_STYLE,
                    find_span(".intel_syntax"),
                    ecx.current_expansion.lint_node_id,
                    "avoid using `.intel_syntax`, Intel syntax is the default",
                );
            }
            if template_str.contains(".att_syntax") {
                ecx.parse_sess().buffer_lint(
                    lint::builtin::BAD_ASM_STYLE,
                    find_span(".att_syntax"),
                    ecx.current_expansion.lint_node_id,
                    "avoid using `.att_syntax`, prefer using `options(att_syntax)` instead",
                );
            }
        }

        // Don't treat raw asm as a format string.
        if args.options.contains(ast::InlineAsmOptions::RAW) {
            template.push(ast::InlineAsmTemplatePiece::String(template_str.to_string()));
            let template_num_lines = 1 + template_str.matches('\n').count();
            line_spans.extend(std::iter::repeat(template_sp).take(template_num_lines));
            continue;
        }

        let mut parser = parse::Parser::new(
            template_str,
            str_style,
            template_snippet,
            false,
            parse::ParseMode::InlineAsm,
        );
        parser.curarg = curarg;

        let mut unverified_pieces = Vec::new();
        while let Some(piece) = parser.next() {
            if !parser.errors.is_empty() {
                break;
            } else {
                unverified_pieces.push(piece);
            }
        }

        if !parser.errors.is_empty() {
            let err = parser.errors.remove(0);
            let err_sp = template_span.from_inner(InnerSpan::new(err.span.start, err.span.end));
            let msg = format!("invalid asm template string: {}", err.description);
            let mut e = ecx.struct_span_err(err_sp, msg);
            e.span_label(err_sp, err.label + " in asm template string");
            if let Some(note) = err.note {
                e.note(note);
            }
            if let Some((label, span)) = err.secondary_label {
                let err_sp = template_span.from_inner(InnerSpan::new(span.start, span.end));
                e.span_label(err_sp, label);
            }
            e.emit();
            return None;
        }

        curarg = parser.curarg;

        let mut arg_spans = parser
            .arg_places
            .iter()
            .map(|span| template_span.from_inner(InnerSpan::new(span.start, span.end)));
        for piece in unverified_pieces {
            match piece {
                parse::Piece::String(s) => {
                    template.push(ast::InlineAsmTemplatePiece::String(s.to_string()))
                }
                parse::Piece::NextArgument(arg) => {
                    let span = arg_spans.next().unwrap_or(template_sp);

                    let operand_idx = match arg.position {
                        parse::ArgumentIs(idx) | parse::ArgumentImplicitlyIs(idx) => {
                            if idx >= args.operands.len()
                                || named_pos.contains_key(&idx)
                                || args.reg_args.contains(idx)
                            {
                                let msg = format!("invalid reference to argument at index {idx}");
                                let mut err = ecx.struct_span_err(span, msg);
                                err.span_label(span, "from here");

                                let positional_args = args.operands.len()
                                    - args.named_args.len()
                                    - args.reg_args.len();
                                let positional = if positional_args != args.operands.len() {
                                    "positional "
                                } else {
                                    ""
                                };
                                let msg = match positional_args {
                                    0 => format!("no {positional}arguments were given"),
                                    1 => format!("there is 1 {positional}argument"),
                                    x => format!("there are {x} {positional}arguments"),
                                };
                                err.note(msg);

                                if named_pos.contains_key(&idx) {
                                    err.span_label(args.operands[idx].1, "named argument");
                                    err.span_note(
                                        args.operands[idx].1,
                                        "named arguments cannot be referenced by position",
                                    );
                                } else if args.reg_args.contains(idx) {
                                    err.span_label(
                                        args.operands[idx].1,
                                        "explicit register argument",
                                    );
                                    err.span_note(
                                        args.operands[idx].1,
                                        "explicit register arguments cannot be used in the asm template",
                                    );
                                    err.span_help(
                                        args.operands[idx].1,
                                        "use the register name directly in the assembly code",
                                    );
                                }
                                err.emit();
                                None
                            } else {
                                Some(idx)
                            }
                        }
                        parse::ArgumentNamed(name) => {
                            match args.named_args.get(&Symbol::intern(name)) {
                                Some(&idx) => Some(idx),
                                None => {
                                    let msg = format!("there is no argument named `{name}`");
                                    let span = arg.position_span;
                                    ecx.struct_span_err(
                                        template_span
                                            .from_inner(InnerSpan::new(span.start, span.end)),
                                        msg,
                                    )
                                    .emit();
                                    None
                                }
                            }
                        }
                    };

                    let mut chars = arg.format.ty.chars();
                    let mut modifier = chars.next();
                    if chars.next().is_some() {
                        let span = arg
                            .format
                            .ty_span
                            .map(|sp| template_sp.from_inner(InnerSpan::new(sp.start, sp.end)))
                            .unwrap_or(template_sp);
                        ecx.emit_err(errors::AsmModifierInvalid { span });
                        modifier = None;
                    }

                    if let Some(operand_idx) = operand_idx {
                        used[operand_idx] = true;
                        template.push(ast::InlineAsmTemplatePiece::Placeholder {
                            operand_idx,
                            modifier,
                            span,
                        });
                    }
                }
            }
        }

        if parser.line_spans.is_empty() {
            let template_num_lines = 1 + template_str.matches('\n').count();
            line_spans.extend(std::iter::repeat(template_sp).take(template_num_lines));
        } else {
            line_spans.extend(
                parser
                    .line_spans
                    .iter()
                    .map(|span| template_span.from_inner(InnerSpan::new(span.start, span.end))),
            );
        };
    }

    let mut unused_operands = vec![];
    let mut help_str = String::new();
    for (idx, used) in used.into_iter().enumerate() {
        if !used {
            let msg = if let Some(sym) = named_pos.get(&idx) {
                help_str.push_str(&format!(" {{{}}}", sym));
                "named argument never used"
            } else {
                help_str.push_str(&format!(" {{{}}}", idx));
                "argument never used"
            };
            unused_operands.push((args.operands[idx].1, msg));
        }
    }
    match unused_operands.len() {
        0 => {}
        1 => {
            let (sp, msg) = unused_operands.into_iter().next().unwrap();
            let mut err = ecx.struct_span_err(sp, msg);
            err.span_label(sp, msg);
            err.help(format!(
                "if this argument is intentionally unused, \
                 consider using it in an asm comment: `\"/*{help_str} */\"`"
            ));
            err.emit();
        }
        _ => {
            let mut err = ecx.struct_span_err(
                unused_operands.iter().map(|&(sp, _)| sp).collect::<Vec<Span>>(),
                "multiple unused asm arguments",
            );
            for (sp, msg) in unused_operands {
                err.span_label(sp, msg);
            }
            err.help(format!(
                "if these arguments are intentionally unused, \
                 consider using them in an asm comment: `\"/*{help_str} */\"`"
            ));
            err.emit();
        }
    }

    Some(ast::InlineAsm {
        template,
        template_strs: template_strs.into_boxed_slice(),
        operands: args.operands,
        clobber_abis: args.clobber_abis,
        options: args.options,
        line_spans,
    })
}

pub(super) fn expand_asm<'cx>(
    ecx: &'cx mut ExtCtxt<'_>,
    sp: Span,
    tts: TokenStream,
) -> Box<dyn base::MacResult + 'cx> {
    match parse_args(ecx, sp, tts, false) {
        Ok(args) => {
            let expr = if let Some(inline_asm) = expand_preparsed_asm(ecx, args) {
                P(ast::Expr {
                    id: ast::DUMMY_NODE_ID,
                    kind: ast::ExprKind::InlineAsm(P(inline_asm)),
                    span: sp,
                    attrs: ast::AttrVec::new(),
                    tokens: None,
                })
            } else {
                DummyResult::raw_expr(sp, true)
            };
            MacEager::expr(expr)
        }
        Err(mut err) => {
            err.emit();
            DummyResult::any(sp)
        }
    }
}

pub(super) fn expand_global_asm<'cx>(
    ecx: &'cx mut ExtCtxt<'_>,
    sp: Span,
    tts: TokenStream,
) -> Box<dyn base::MacResult + 'cx> {
    match parse_args(ecx, sp, tts, true) {
        Ok(args) => {
            if let Some(inline_asm) = expand_preparsed_asm(ecx, args) {
                MacEager::items(smallvec![P(ast::Item {
                    ident: Ident::empty(),
                    attrs: ast::AttrVec::new(),
                    id: ast::DUMMY_NODE_ID,
                    kind: ast::ItemKind::GlobalAsm(Box::new(inline_asm)),
                    vis: ast::Visibility {
                        span: sp.shrink_to_lo(),
                        kind: ast::VisibilityKind::Inherited,
                        tokens: None,
                    },
                    span: ecx.with_def_site_ctxt(sp),
                    tokens: None,
                })])
            } else {
                DummyResult::any(sp)
            }
        }
        Err(mut err) => {
            err.emit();
            DummyResult::any(sp)
        }
    }
}