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Commit | Line | Data |
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29967ef6 | 1 | use crate::transform::MirPass; |
e74abb32 | 2 | use rustc_index::vec::{Idx, IndexVec}; |
ba9703b0 XL |
3 | use rustc_middle::mir::*; |
4 | use rustc_middle::ty::TyCtxt; | |
3157f602 | 5 | |
3b2f2976 XL |
6 | #[derive(PartialEq)] |
7 | pub enum AddCallGuards { | |
8 | AllCallEdges, | |
9 | CriticalCallEdges, | |
10 | } | |
11 | pub use self::AddCallGuards::*; | |
3157f602 XL |
12 | |
13 | /** | |
14 | * Breaks outgoing critical edges for call terminators in the MIR. | |
15 | * | |
16 | * Critical edges are edges that are neither the only edge leaving a | |
17 | * block, nor the only edge entering one. | |
18 | * | |
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 | |
94b46f34 | 23 | * codegened to LLVM invoke instructions, because invoke is a block terminator |
3157f602 XL |
24 | * in LLVM so we can't insert any code to handle the call's result into the |
25 | * block that performs the call. | |
26 | * | |
27 | * This function will break those edges by inserting new blocks along them. | |
28 | * | |
29 | * NOTE: Simplify CFG will happily undo most of the work this pass does. | |
30 | * | |
31 | */ | |
32 | ||
e1599b0c | 33 | impl<'tcx> MirPass<'tcx> for AddCallGuards { |
29967ef6 | 34 | fn run_pass(&self, _tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) { |
dc9dc135 | 35 | self.add_call_guards(body); |
cc61c64b XL |
36 | } |
37 | } | |
38 | ||
3b2f2976 | 39 | impl AddCallGuards { |
f9f354fc | 40 | pub fn add_call_guards(&self, body: &mut Body<'_>) { |
60c5eb7d | 41 | let pred_count: IndexVec<_, _> = body.predecessors().iter().map(|ps| ps.len()).collect(); |
3157f602 | 42 | |
3b2f2976 XL |
43 | // We need a place to store the new blocks generated |
44 | let mut new_blocks = Vec::new(); | |
3157f602 | 45 | |
dc9dc135 | 46 | let cur_len = body.basic_blocks().len(); |
3157f602 | 47 | |
dc9dc135 | 48 | for block in body.basic_blocks_mut() { |
3b2f2976 XL |
49 | match block.terminator { |
50 | Some(Terminator { | |
dfeec247 XL |
51 | kind: |
52 | TerminatorKind::Call { | |
53 | destination: Some((_, ref mut destination)), | |
54 | cleanup, | |
55 | .. | |
56 | }, | |
57 | source_info, | |
58 | }) if pred_count[*destination] > 1 | |
59 | && (cleanup.is_some() || self == &AllCallEdges) => | |
3b2f2976 XL |
60 | { |
61 | // It's a critical edge, break it | |
62 | let call_guard = BasicBlockData { | |
63 | statements: vec![], | |
64 | is_cleanup: block.is_cleanup, | |
65 | terminator: Some(Terminator { | |
66 | source_info, | |
dfeec247 XL |
67 | kind: TerminatorKind::Goto { target: *destination }, |
68 | }), | |
3b2f2976 | 69 | }; |
3157f602 | 70 | |
3b2f2976 XL |
71 | // Get the index it will be when inserted into the MIR |
72 | let idx = cur_len + new_blocks.len(); | |
73 | new_blocks.push(call_guard); | |
74 | *destination = BasicBlock::new(idx); | |
75 | } | |
76 | _ => {} | |
3157f602 XL |
77 | } |
78 | } | |
79 | ||
3b2f2976 | 80 | debug!("Broke {} N edges", new_blocks.len()); |
3157f602 | 81 | |
dc9dc135 | 82 | body.basic_blocks_mut().extend(new_blocks); |
3b2f2976 | 83 | } |
3157f602 | 84 | } |