3 use rustc_data_structures::indexed_vec::{Idx, IndexVec};
4 use crate::transform::{MirPass, MirSource};
7 pub enum AddCallGuards {
11 pub use self::AddCallGuards::*;
14 * Breaks outgoing critical edges for call terminators in the MIR.
16 * Critical edges are edges that are neither the only edge leaving a
17 * block, nor the only edge entering one.
19 * When you want something to happen "along" an edge, you can either
20 * do at the end of the predecessor block, or at the start of the
21 * successor block. Critical edges have to be broken in order to prevent
22 * "edge actions" from affecting other edges. We need this for calls that are
23 * codegened to LLVM invoke instructions, because invoke is a block terminator
24 * in LLVM so we can't insert any code to handle the call's result into the
25 * block that performs the call.
27 * This function will break those edges by inserting new blocks along them.
29 * NOTE: Simplify CFG will happily undo most of the work this pass does.
33 impl MirPass for AddCallGuards {
34 fn run_pass<'a, 'tcx>(&self,
35 _tcx: TyCtxt<'a, 'tcx, 'tcx>,
36 _src: MirSource<'tcx>,
37 mir: &mut Body<'tcx>) {
38 self.add_call_guards(mir);
43 pub fn add_call_guards(&self, mir: &mut Body<'_>) {
44 let pred_count: IndexVec<_, _> =
45 mir.predecessors().iter().map(|ps| ps.len()).collect();
47 // We need a place to store the new blocks generated
48 let mut new_blocks = Vec::new();
50 let cur_len = mir.basic_blocks().len();
52 for block in mir.basic_blocks_mut() {
53 match block.terminator {
55 kind: TerminatorKind::Call {
56 destination: Some((_, ref mut destination)),
60 }) if pred_count[*destination] > 1 &&
61 (cleanup.is_some() || self == &AllCallEdges) =>
63 // It's a critical edge, break it
64 let call_guard = BasicBlockData {
66 is_cleanup: block.is_cleanup,
67 terminator: Some(Terminator {
69 kind: TerminatorKind::Goto { target: *destination }
73 // Get the index it will be when inserted into the MIR
74 let idx = cur_len + new_blocks.len();
75 new_blocks.push(call_guard);
76 *destination = BasicBlock::new(idx);
82 debug!("Broke {} N edges", new_blocks.len());
84 mir.basic_blocks_mut().extend(new_blocks);