rustc_ast_lowering/

asm.rs

use std::collections::hash_map::Entry;

use rustc_ast::*;
use rustc_data_structures::fx::{FxHashMap, FxHashSet, FxIndexMap};
use rustc_errors::msg;
use rustc_hir as hir;
use rustc_hir::def::{DefKind, Res};
use rustc_session::errors::feature_err;
use rustc_span::{Span, sym};
use rustc_target::asm;

use crate::diagnostics::{
    AbiSpecifiedMultipleTimes, AttSyntaxOnlyX86, ClobberAbiNotSupported,
    InlineAsmUnsupportedTarget, InvalidAbiClobberAbi, InvalidAsmTemplateModifierConst,
    InvalidAsmTemplateModifierLabel, InvalidAsmTemplateModifierRegClass,
    InvalidAsmTemplateModifierRegClassSub, InvalidAsmTemplateModifierSym, InvalidRegister,
    InvalidRegisterClass, RegisterClassOnlyClobber, RegisterClassOnlyClobberStable,
    RegisterConflict,
};
use crate::{
    AllowReturnTypeNotation, ImplTraitContext, ImplTraitPosition, LoweringContext, ParamMode,
};

impl<'hir> LoweringContext<'_, 'hir> {
    pub(crate) fn lower_inline_asm(
        &mut self,
        sp: Span,
        asm: &InlineAsm,
    ) -> &'hir hir::InlineAsm<'hir> {
        // Rustdoc needs to support asm! from foreign architectures: don't try
        // lowering the register constraints in this case.
        let asm_arch =
            if self.tcx.sess.opts.actually_rustdoc { None } else { self.tcx.sess.asm_arch };
        if asm_arch.is_none() && !self.tcx.sess.opts.actually_rustdoc {
            self.dcx().emit_err(InlineAsmUnsupportedTarget { span: sp });
        }
        if let Some(asm_arch) = asm_arch {
            // Inline assembly is currently only stable for these architectures.
            // (See also compiletest's `has_asm_support`.)
            let is_stable = matches!(
                asm_arch,
                asm::InlineAsmArch::X86
                    | asm::InlineAsmArch::X86_64
                    | asm::InlineAsmArch::Arm
                    | asm::InlineAsmArch::AArch64
                    | asm::InlineAsmArch::Arm64EC
                    | asm::InlineAsmArch::RiscV32
                    | asm::InlineAsmArch::RiscV64
                    | asm::InlineAsmArch::LoongArch32
                    | asm::InlineAsmArch::LoongArch64
                    | asm::InlineAsmArch::S390x
                    | asm::InlineAsmArch::PowerPC
                    | asm::InlineAsmArch::PowerPC64
            );
            if !is_stable
                && !self.tcx.features().asm_experimental_arch()
                && sp
                    .ctxt()
                    .outer_expn_data()
                    .allow_internal_unstable
                    .filter(|features| features.contains(&sym::asm_experimental_arch))
                    .is_none()
            {
                feature_err(
                    &self.tcx.sess,
                    sym::asm_experimental_arch,
                    sp,
                    msg!("inline assembly is not stable yet on this architecture"),
                )
                .emit();
            }
        }
        let allow_experimental_reg = self.tcx.features().asm_experimental_reg();
        if asm.options.contains(InlineAsmOptions::ATT_SYNTAX)
            && !matches!(asm_arch, Some(asm::InlineAsmArch::X86 | asm::InlineAsmArch::X86_64))
            && !self.tcx.sess.opts.actually_rustdoc
        {
            self.dcx().emit_err(AttSyntaxOnlyX86 { span: sp });
        }
        if asm.options.contains(InlineAsmOptions::MAY_UNWIND) && !self.tcx.features().asm_unwind() {
            feature_err(
                &self.tcx.sess,
                sym::asm_unwind,
                sp,
                msg!("the `may_unwind` option is unstable"),
            )
            .emit();
        }

        let mut clobber_abis = FxIndexMap::default();
        if let Some(asm_arch) = asm_arch {
            for (abi_name, abi_span) in &asm.clobber_abis {
                match asm::InlineAsmClobberAbi::parse(
                    asm_arch,
                    &self.tcx.sess.target,
                    &self.tcx.sess.unstable_target_features,
                    *abi_name,
                ) {
                    Ok(abi) => {
                        // If the abi was already in the list, emit an error
                        match clobber_abis.get(&abi) {
                            Some((prev_name, prev_sp)) => {
                                // Multiple different abi names may actually be the same ABI
                                // If the specified ABIs are not the same name, alert the user that they resolve to the same ABI
                                let source_map = self.tcx.sess.source_map();
                                let equivalent = source_map.span_to_snippet(*prev_sp)
                                    != source_map.span_to_snippet(*abi_span);

                                self.dcx().emit_err(AbiSpecifiedMultipleTimes {
                                    abi_span: *abi_span,
                                    prev_name: *prev_name,
                                    prev_span: *prev_sp,
                                    equivalent,
                                });
                            }
                            None => {
                                clobber_abis.insert(abi, (*abi_name, *abi_span));
                            }
                        }
                    }
                    Err(&[]) => {
                        self.dcx().emit_err(ClobberAbiNotSupported { abi_span: *abi_span });
                    }
                    Err(supported_abis) => {
                        self.dcx().emit_err(InvalidAbiClobberAbi {
                            abi_span: *abi_span,
                            supported_abis: supported_abis.to_vec().into(),
                        });
                    }
                }
            }
        }

        // Lower operands to HIR. We use dummy register classes if an error
        // occurs during lowering because we still need to be able to produce a
        // valid HIR.
        let sess = self.tcx.sess;
        let mut operands: Vec<_> = asm
            .operands
            .iter()
            .map(|(op, op_sp)| {
                let lower_reg = |&reg: &_| match reg {
                    InlineAsmRegOrRegClass::Reg(reg) => {
                        asm::InlineAsmRegOrRegClass::Reg(if let Some(asm_arch) = asm_arch {
                            asm::InlineAsmReg::parse(asm_arch, reg).unwrap_or_else(|error| {
                                self.dcx().emit_err(InvalidRegister {
                                    op_span: *op_sp,
                                    reg,
                                    error,
                                });
                                asm::InlineAsmReg::Err
                            })
                        } else {
                            asm::InlineAsmReg::Err
                        })
                    }
                    InlineAsmRegOrRegClass::RegClass(reg_class) => {
                        asm::InlineAsmRegOrRegClass::RegClass(if let Some(asm_arch) = asm_arch {
                            asm::InlineAsmRegClass::parse(asm_arch, reg_class).unwrap_or_else(
                                |supported_register_classes| {
                                    self.dcx().emit_err(InvalidRegisterClass {
                                        op_span: *op_sp,
                                        reg_class,
                                        supported_register_classes: supported_register_classes
                                            .to_vec()
                                            .into(),
                                    });
                                    asm::InlineAsmRegClass::Err
                                },
                            )
                        } else {
                            asm::InlineAsmRegClass::Err
                        })
                    }
                };

                let op = match op {
                    InlineAsmOperand::In { reg, expr } => hir::InlineAsmOperand::In {
                        reg: lower_reg(reg),
                        expr: self.lower_expr(expr),
                    },
                    InlineAsmOperand::Out { reg, late, expr } => hir::InlineAsmOperand::Out {
                        reg: lower_reg(reg),
                        late: *late,
                        expr: expr.as_ref().map(|expr| self.lower_expr(expr)),
                    },
                    InlineAsmOperand::InOut { reg, late, expr } => hir::InlineAsmOperand::InOut {
                        reg: lower_reg(reg),
                        late: *late,
                        expr: self.lower_expr(expr),
                    },
                    InlineAsmOperand::SplitInOut { reg, late, in_expr, out_expr } => {
                        hir::InlineAsmOperand::SplitInOut {
                            reg: lower_reg(reg),
                            late: *late,
                            in_expr: self.lower_expr(in_expr),
                            out_expr: out_expr.as_ref().map(|expr| self.lower_expr(expr)),
                        }
                    }
                    InlineAsmOperand::Const { anon_const } => hir::InlineAsmOperand::Const {
                        anon_const: self.lower_const_block(anon_const),
                    },
                    InlineAsmOperand::Sym { sym } => {
                        let static_def_id = self
                            .get_partial_res(sym.id)
                            .and_then(|res| res.full_res())
                            .and_then(|res| match res {
                                Res::Def(DefKind::Static { .. }, def_id) => Some(def_id),
                                _ => None,
                            });

                        if let Some(def_id) = static_def_id {
                            let path = self.lower_qpath(
                                sym.id,
                                &sym.qself,
                                &sym.path,
                                ParamMode::Optional,
                                AllowReturnTypeNotation::No,
                                ImplTraitContext::Disallowed(ImplTraitPosition::Path),
                                None,
                            );
                            hir::InlineAsmOperand::SymStatic { path, def_id }
                        } else {
                            // Replace the InlineAsmSym AST node with an
                            // Expr using the name node id.
                            let expr = Expr {
                                id: sym.id,
                                kind: ExprKind::Path(sym.qself.clone(), sym.path.clone()),
                                span: *op_sp,
                                attrs: AttrVec::new(),
                                tokens: None,
                            };

                            hir::InlineAsmOperand::SymFn { expr: self.lower_expr(&expr) }
                        }
                    }
                    InlineAsmOperand::Label { block } => {
                        hir::InlineAsmOperand::Label { block: self.lower_block(block, false) }
                    }
                };
                (op, self.lower_span(*op_sp))
            })
            .collect();

        // Validate template modifiers against the register classes for the operands
        for p in &asm.template {
            if let InlineAsmTemplatePiece::Placeholder {
                operand_idx,
                modifier: Some(modifier),
                span: placeholder_span,
            } = *p
            {
                let op_sp = asm.operands[operand_idx].1;
                match &operands[operand_idx].0 {
                    hir::InlineAsmOperand::In { reg, .. }
                    | hir::InlineAsmOperand::Out { reg, .. }
                    | hir::InlineAsmOperand::InOut { reg, .. }
                    | hir::InlineAsmOperand::SplitInOut { reg, .. } => {
                        let class = reg.reg_class();
                        if class == asm::InlineAsmRegClass::Err {
                            continue;
                        }
                        let valid_modifiers = class.valid_modifiers(asm_arch.unwrap());
                        if !valid_modifiers.contains(&modifier) {
                            let sub = if valid_modifiers.is_empty() {
                                InvalidAsmTemplateModifierRegClassSub::DoesNotSupportModifier {
                                    class_name: class.name(),
                                }
                            } else {
                                InvalidAsmTemplateModifierRegClassSub::SupportModifier {
                                    class_name: class.name(),
                                    modifiers: valid_modifiers.to_vec().into(),
                                }
                            };
                            self.dcx().emit_err(InvalidAsmTemplateModifierRegClass {
                                placeholder_span,
                                op_span: op_sp,
                                modifier: modifier.to_string(),
                                sub,
                            });
                        }
                    }
                    hir::InlineAsmOperand::Const { .. } => {
                        self.dcx().emit_err(InvalidAsmTemplateModifierConst {
                            placeholder_span,
                            op_span: op_sp,
                        });
                    }
                    hir::InlineAsmOperand::SymFn { .. }
                    | hir::InlineAsmOperand::SymStatic { .. } => {
                        self.dcx().emit_err(InvalidAsmTemplateModifierSym {
                            placeholder_span,
                            op_span: op_sp,
                        });
                    }
                    hir::InlineAsmOperand::Label { .. } => {
                        self.dcx().emit_err(InvalidAsmTemplateModifierLabel {
                            placeholder_span,
                            op_span: op_sp,
                        });
                    }
                }
            }
        }

        let mut used_input_regs = FxHashMap::default();
        let mut used_output_regs = FxHashMap::default();

        for (idx, &(ref op, op_sp)) in operands.iter().enumerate() {
            if let Some(reg) = op.reg() {
                let reg_class = reg.reg_class();
                if reg_class == asm::InlineAsmRegClass::Err {
                    continue;
                }

                // Some register classes can only be used as clobbers. This
                // means that we disallow passing a value in/out of the asm and
                // require that the operand name an explicit register, not a
                // register class.
                if reg_class.is_clobber_only(asm_arch.unwrap(), allow_experimental_reg)
                    && !op.is_clobber()
                {
                    if allow_experimental_reg || reg_class.is_clobber_only(asm_arch.unwrap(), true)
                    {
                        // always clobber-only
                        self.dcx().emit_err(RegisterClassOnlyClobber {
                            op_span: op_sp,
                            reg_class_name: reg_class.name(),
                        });
                    } else {
                        // clobber-only in stable
                        self.tcx
                            .sess
                            .create_feature_err(
                                RegisterClassOnlyClobberStable {
                                    op_span: op_sp,
                                    reg_class_name: reg_class.name(),
                                },
                                sym::asm_experimental_reg,
                            )
                            .emit();
                    }
                    continue;
                }

                // Check for conflicts between explicit register operands.
                if let asm::InlineAsmRegOrRegClass::Reg(reg) = reg {
                    let (input, output) = match op {
                        hir::InlineAsmOperand::In { .. } => (true, false),

                        // Late output do not conflict with inputs, but normal outputs do
                        hir::InlineAsmOperand::Out { late, .. } => (!late, true),

                        hir::InlineAsmOperand::InOut { .. }
                        | hir::InlineAsmOperand::SplitInOut { .. } => (true, true),

                        hir::InlineAsmOperand::Const { .. }
                        | hir::InlineAsmOperand::SymFn { .. }
                        | hir::InlineAsmOperand::SymStatic { .. }
                        | hir::InlineAsmOperand::Label { .. } => {
                            unreachable!("{op:?} is not a register operand");
                        }
                    };

                    // Flag to output the error only once per operand
                    let mut skip = false;

                    let mut check = |used_regs: &mut FxHashMap<asm::InlineAsmReg, usize>,
                                     input,
                                     r: asm::InlineAsmReg| {
                        match used_regs.entry(r) {
                            Entry::Occupied(o) => {
                                if skip {
                                    return;
                                }
                                skip = true;

                                let idx2 = *o.get();
                                let (ref op2, op_sp2) = operands[idx2];

                                let in_out = match (op, op2) {
                                    (
                                        hir::InlineAsmOperand::In { .. },
                                        hir::InlineAsmOperand::Out { late, .. },
                                    )
                                    | (
                                        hir::InlineAsmOperand::Out { late, .. },
                                        hir::InlineAsmOperand::In { .. },
                                    ) => {
                                        assert!(!*late);
                                        let out_op_sp = if input { op_sp2 } else { op_sp };
                                        Some(out_op_sp)
                                    }
                                    _ => None,
                                };
                                let reg_str = |idx| -> &str {
                                    // HIR asm doesn't preserve the original alias string of the explicit register,
                                    // so we have to retrieve it from AST
                                    let (op, _): &(InlineAsmOperand, Span) = &asm.operands[idx];
                                    if let Some(ast::InlineAsmRegOrRegClass::Reg(reg_sym)) =
                                        op.reg()
                                    {
                                        reg_sym.as_str()
                                    } else {
                                        unreachable!("{op:?} is not a register operand");
                                    }
                                };

                                self.dcx().emit_err(RegisterConflict {
                                    op_span1: op_sp,
                                    op_span2: op_sp2,
                                    reg1_name: reg_str(idx),
                                    reg2_name: reg_str(idx2),
                                    in_out,
                                });
                            }
                            Entry::Vacant(v) => {
                                if r == reg {
                                    v.insert(idx);
                                }
                            }
                        }
                    };
                    let mut overlapping_with = vec![];
                    reg.overlapping_regs(|r| {
                        overlapping_with.push(r);
                    });
                    for r in overlapping_with {
                        if input {
                            check(&mut used_input_regs, true, r);
                        }
                        if output {
                            check(&mut used_output_regs, false, r);
                        }
                    }
                }
            }
        }

        // If a clobber_abi is specified, add the necessary clobbers to the
        // operands list.
        let mut clobbered = FxHashSet::default();
        for (abi, (_, abi_span)) in clobber_abis {
            for &clobber in abi.clobbered_regs() {
                // Don't emit a clobber for a register already clobbered
                if clobbered.contains(&clobber) {
                    continue;
                }

                let mut overlapping_with = vec![];
                clobber.overlapping_regs(|reg| {
                    overlapping_with.push(reg);
                });
                let output_used =
                    overlapping_with.iter().any(|reg| used_output_regs.contains_key(&reg));

                if !output_used {
                    operands.push((
                        hir::InlineAsmOperand::Out {
                            reg: asm::InlineAsmRegOrRegClass::Reg(clobber),
                            late: true,
                            expr: None,
                        },
                        self.lower_span(abi_span),
                    ));
                    clobbered.insert(clobber);
                }
            }
        }

        // Feature gate checking for `asm_goto_with_outputs`.
        if let Some((_, op_sp)) =
            operands.iter().find(|(op, _)| matches!(op, hir::InlineAsmOperand::Label { .. }))
        {
            // Check if an output operand is used.
            let output_operand_used = operands.iter().any(|(op, _)| {
                matches!(
                    op,
                    hir::InlineAsmOperand::Out { expr: Some(_), .. }
                        | hir::InlineAsmOperand::InOut { .. }
                        | hir::InlineAsmOperand::SplitInOut { out_expr: Some(_), .. }
                )
            });
            if output_operand_used && !self.tcx.features().asm_goto_with_outputs() {
                feature_err(
                    sess,
                    sym::asm_goto_with_outputs,
                    *op_sp,
                    msg!("using both label and output operands for inline assembly is unstable"),
                )
                .emit();
            }
        }

        let operands = self.arena.alloc_from_iter(operands);
        let template = self.arena.alloc_from_iter(asm.template.iter().cloned());
        let template_strs = self.arena.alloc_from_iter(
            asm.template_strs
                .iter()
                .map(|(sym, snippet, span)| (*sym, *snippet, self.lower_span(*span))),
        );
        let line_spans =
            self.arena.alloc_from_iter(asm.line_spans.iter().map(|span| self.lower_span(*span)));
        let hir_asm = hir::InlineAsm {
            asm_macro: asm.asm_macro,
            template,
            template_strs,
            operands,
            options: asm.options,
            line_spans,
        };
        self.arena.alloc(hir_asm)
    }
}