2 use rustc_index::vec::{Idx, IndexVec};
3 use rustc_middle::mir::*;
4 use rustc_middle::ty::TyCtxt;
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<'tcx> MirPass<'tcx> for AddCallGuards {
34 fn run_pass(&self, _tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
35 self.add_call_guards(body);
40 pub fn add_call_guards(&self, body: &mut Body<'_>) {
41 let mut pred_count: IndexVec<_, _> =
42 body.basic_blocks.predecessors().iter().map(|ps| ps.len()).collect();
43 pred_count[START_BLOCK] += 1;
45 // We need a place to store the new blocks generated
46 let mut new_blocks = Vec::new();
48 let cur_len = body.basic_blocks.len();
50 for block in body.basic_blocks_mut() {
51 match block.terminator {
53 kind: TerminatorKind::Call { target: Some(ref mut destination), cleanup, .. },
55 }) if pred_count[*destination] > 1
56 && (cleanup.is_some() || self == &AllCallEdges) =>
58 // It's a critical edge, break it
59 let call_guard = BasicBlockData {
61 is_cleanup: block.is_cleanup,
62 terminator: Some(Terminator {
64 kind: TerminatorKind::Goto { target: *destination },
68 // Get the index it will be when inserted into the MIR
69 let idx = cur_len + new_blocks.len();
70 new_blocks.push(call_guard);
71 *destination = BasicBlock::new(idx);
77 debug!("Broke {} N edges", new_blocks.len());
79 body.basic_blocks_mut().extend(new_blocks);