compiler/rustc_mir_build/src/builder/cfg.rs

//! Routines for manipulating the control-flow graph.

use rustc_data_structures::thin_vec::ThinVec;
use rustc_middle::mir::*;
use rustc_middle::ty::TyCtxt;
use tracing::debug;

use crate::builder::CFG;

impl<'tcx> CFG<'tcx> {
    pub(crate) fn block_data(&self, blk: BasicBlock) -> &BasicBlockData<'tcx> {
        &self.basic_blocks[blk]
    }

    pub(crate) fn block_data_mut(&mut self, blk: BasicBlock) -> &mut BasicBlockData<'tcx> {
        &mut self.basic_blocks[blk]
    }

    // llvm.org/PR32488 makes this function use an excess of stack space. Mark
    // it as #[inline(never)] to keep rustc's stack use in check.
    #[inline(never)]
    pub(crate) fn start_new_block(&mut self) -> BasicBlock {
        self.basic_blocks.push(BasicBlockData::new(None, false))
    }

    pub(crate) fn start_new_cleanup_block(&mut self) -> BasicBlock {
        let bb = self.start_new_block();
        self.block_data_mut(bb).is_cleanup = true;
        bb
    }

    pub(crate) fn push(&mut self, block: BasicBlock, statement: Statement<'tcx>) {
        debug!("push({:?}, {:?})", block, statement);
        self.block_data_mut(block).statements.push(statement);
    }

    pub(crate) fn push_assign(
        &mut self,
        block: BasicBlock,
        source_info: SourceInfo,
        place: Place<'tcx>,
        rvalue: Rvalue<'tcx>,
    ) {
        self.push(
            block,
            Statement::new(source_info, StatementKind::Assign(Box::new((place, rvalue)))),
        );
    }

    pub(crate) fn push_assign_constant(
        &mut self,
        block: BasicBlock,
        source_info: SourceInfo,
        temp: Place<'tcx>,
        constant: ConstOperand<'tcx>,
    ) {
        self.push_assign(
            block,
            source_info,
            temp,
            Rvalue::Use(Operand::Constant(Box::new(constant)), WithRetag::Yes),
        );
    }

    pub(crate) fn push_assign_unit(
        &mut self,
        block: BasicBlock,
        source_info: SourceInfo,
        place: Place<'tcx>,
        tcx: TyCtxt<'tcx>,
    ) {
        self.push_assign(
            block,
            source_info,
            place,
            Rvalue::Use(
                Operand::Constant(Box::new(ConstOperand {
                    span: source_info.span,
                    user_ty: None,
                    const_: Const::zero_sized(tcx.types.unit),
                })),
                WithRetag::Yes,
            ),
        );
    }

    pub(crate) fn push_fake_read(
        &mut self,
        block: BasicBlock,
        source_info: SourceInfo,
        cause: FakeReadCause,
        place: Place<'tcx>,
    ) {
        let kind = StatementKind::FakeRead(Box::new((cause, place)));
        let stmt = Statement::new(source_info, kind);
        self.push(block, stmt);
    }

    pub(crate) fn push_place_mention(
        &mut self,
        block: BasicBlock,
        source_info: SourceInfo,
        place: Place<'tcx>,
    ) {
        let kind = StatementKind::PlaceMention(Box::new(place));
        let stmt = Statement::new(source_info, kind);
        self.push(block, stmt);
    }

    /// Adds a dummy statement whose only role is to associate a span with its
    /// enclosing block for the purposes of coverage instrumentation.
    ///
    /// This results in more accurate coverage reports for certain kinds of
    /// syntax (e.g. `continue` or `if !`) that would otherwise not appear in MIR.
    pub(crate) fn push_coverage_span_marker(&mut self, block: BasicBlock, source_info: SourceInfo) {
        let kind = StatementKind::Coverage(coverage::CoverageKind::SpanMarker);
        let stmt = Statement::new(source_info, kind);
        self.push(block, stmt);
    }

    pub(crate) fn terminate(
        &mut self,
        block: BasicBlock,
        source_info: SourceInfo,
        kind: TerminatorKind<'tcx>,
    ) -> &mut Terminator<'tcx> {
        debug!("terminating block {:?} <- {:?}", block, kind);
        debug_assert!(
            self.block_data(block).terminator.is_none(),
            "terminate: block {:?}={:?} already has a terminator set",
            block,
            self.block_data(block)
        );
        self.block_data_mut(block).terminator =
            Some(Terminator { source_info, kind, attributes: ThinVec::new() });
        self.block_data_mut(block).terminator.as_mut().unwrap()
    }

    /// In the `origin` block, push a `goto -> target` terminator.
    pub(crate) fn goto(
        &mut self,
        origin: BasicBlock,
        source_info: SourceInfo,
        target: BasicBlock,
    ) -> &mut Terminator<'tcx> {
        self.terminate(origin, source_info, TerminatorKind::Goto { target })
    }
}