diff --git a/src/librustc_driver/driver.rs b/src/librustc_driver/driver.rs index da36cb7c2e4..46356add8c6 100644 --- a/src/librustc_driver/driver.rs +++ b/src/librustc_driver/driver.rs @@ -1036,7 +1036,7 @@ pub fn phase_4_translate_to_llvm<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, passes.push_pass(box mir::transform::no_landing_pads::NoLandingPads); passes.push_pass(box mir::transform::remove_dead_blocks::RemoveDeadBlocks); passes.push_pass(box mir::transform::erase_regions::EraseRegions); - passes.push_pass(box mir::transform::break_critical_edges::BreakCriticalEdges); + passes.push_pass(box mir::transform::break_cleanup_edges::BreakCleanupEdges); passes.run_passes(tcx, &mut mir_map); }); diff --git a/src/librustc_mir/transform/break_cleanup_edges.rs b/src/librustc_mir/transform/break_cleanup_edges.rs new file mode 100644 index 00000000000..0eb6223a71e --- /dev/null +++ b/src/librustc_mir/transform/break_cleanup_edges.rs @@ -0,0 +1,111 @@ +// Copyright 2016 The Rust Project Developers. See the COPYRIGHT +// file at the top-level directory of this distribution and at +// http://rust-lang.org/COPYRIGHT. +// +// Licensed under the Apache License, Version 2.0 or the MIT license +// , at your +// option. This file may not be copied, modified, or distributed +// except according to those terms. + +use rustc::ty::TyCtxt; +use rustc::mir::repr::*; +use rustc::mir::transform::{MirPass, MirSource, Pass}; + +use rustc_data_structures::bitvec::BitVector; + +use pretty; + +use traversal; + +pub struct BreakCleanupEdges; + +/** + * Breaks outgoing critical edges for call terminators in the MIR. + * + * Critical edges are edges that are neither the only edge leaving a + * block, nor the only edge entering one. + * + * When you want something to happen "along" an edge, you can either + * do at the end of the predecessor block, or at the start of the + * successor block. Critical edges have to be broken in order to prevent + * "edge actions" from affecting other edges. We need this for calls that are + * translated to LLVM invoke instructions, because invoke is a block terminator + * in LLVM so we can't insert any code to handle the call's result into the + * block that performs the call. + * + * This function will break those edges by inserting new blocks along them. + * + * NOTE: Simplify CFG will happily undo most of the work this pass does. + * + */ + +impl<'tcx> MirPass<'tcx> for BreakCleanupEdges { + fn run_pass<'a>(&mut self, tcx: TyCtxt<'a, 'tcx, 'tcx>, src: MirSource, mir: &mut Mir<'tcx>) { + let mut pred_count = vec![0u32; mir.basic_blocks.len()]; + + // Build the precedecessor map for the MIR + for (_, data) in traversal::preorder(mir) { + if let Some(ref term) = data.terminator { + for &tgt in term.successors().iter() { + pred_count[tgt.index()] += 1; + } + } + } + + let cleanup_map : BitVector = mir.basic_blocks + .iter().map(|bb| bb.is_cleanup).collect(); + + // We need a place to store the new blocks generated + let mut new_blocks = Vec::new(); + + let bbs = mir.all_basic_blocks(); + let cur_len = mir.basic_blocks.len(); + + for &bb in &bbs { + let data = mir.basic_block_data_mut(bb); + + if let Some(ref mut term) = data.terminator { + if term_is_invoke(term) { + let term_span = term.span; + let term_scope = term.scope; + let succs = term.successors_mut(); + for tgt in succs { + let num_preds = pred_count[tgt.index()]; + if num_preds > 1 { + // It's a critical edge, break it + let goto = Terminator { + span: term_span, + scope: term_scope, + kind: TerminatorKind::Goto { target: *tgt } + }; + let mut data = BasicBlockData::new(Some(goto)); + data.is_cleanup = cleanup_map.contains(tgt.index()); + + // Get the index it will be when inserted into the MIR + let idx = cur_len + new_blocks.len(); + new_blocks.push(data); + *tgt = BasicBlock::new(idx); + } + } + } + } + } + + pretty::dump_mir(tcx, "break_cleanup_edges", &0, src, mir, None); + debug!("Broke {} N edges", new_blocks.len()); + + mir.basic_blocks.extend_from_slice(&new_blocks); + } +} + +impl Pass for BreakCleanupEdges {} + +// Returns true if the terminator is a call that would use an invoke in LLVM. +fn term_is_invoke(term: &Terminator) -> bool { + match term.kind { + TerminatorKind::Call { cleanup: Some(_), .. } | + TerminatorKind::Drop { unwind: Some(_), .. } => true, + _ => false + } +} diff --git a/src/librustc_mir/transform/break_critical_edges.rs b/src/librustc_mir/transform/break_critical_edges.rs deleted file mode 100644 index a6af30b7eec..00000000000 --- a/src/librustc_mir/transform/break_critical_edges.rs +++ /dev/null @@ -1,117 +0,0 @@ -// Copyright 2016 The Rust Project Developers. See the COPYRIGHT -// file at the top-level directory of this distribution and at -// http://rust-lang.org/COPYRIGHT. -// -// Licensed under the Apache License, Version 2.0 or the MIT license -// , at your -// option. This file may not be copied, modified, or distributed -// except according to those terms. - -use rustc::ty::TyCtxt; -use rustc::mir::repr::*; -use rustc::mir::transform::{MirPass, MirSource, Pass}; - -use rustc_data_structures::bitvec::BitVector; - -use traversal; - -pub struct BreakCriticalEdges; - -/** - * Breaks critical edges in the MIR. - * - * Critical edges are edges that are neither the only edge leaving a - * block, nor the only edge entering one. - * - * When you want something to happen "along" an edge, you can either - * do at the end of the predecessor block, or at the start of the - * successor block. Critical edges have to be broken in order to prevent - * "edge actions" from affecting other edges. - * - * This function will break those edges by inserting new blocks along them. - * - * A special case is Drop and Call terminators with unwind/cleanup successors, - * They use `invoke` in LLVM, which terminates a block, meaning that code cannot - * be inserted after them, so even if an edge is the only edge leaving a block - * like that, we still insert blocks if the edge is one of many entering the - * target. - * - * NOTE: Simplify CFG will happily undo most of the work this pass does. - * - */ - -impl<'tcx> MirPass<'tcx> for BreakCriticalEdges { - fn run_pass<'a>(&mut self, _: TyCtxt<'a, 'tcx, 'tcx>, - _: MirSource, mir: &mut Mir<'tcx>) { - break_critical_edges(mir); - } -} - -impl Pass for BreakCriticalEdges {} - -fn break_critical_edges(mir: &mut Mir) { - let mut pred_count = vec![0u32; mir.basic_blocks.len()]; - - // Build the precedecessor map for the MIR - for (_, data) in traversal::preorder(mir) { - if let Some(ref term) = data.terminator { - for &tgt in term.successors().iter() { - pred_count[tgt.index()] += 1; - } - } - } - - let cleanup_map : BitVector = mir.basic_blocks - .iter().map(|bb| bb.is_cleanup).collect(); - - // We need a place to store the new blocks generated - let mut new_blocks = Vec::new(); - - let bbs = mir.all_basic_blocks(); - let cur_len = mir.basic_blocks.len(); - - for &bb in &bbs { - let data = mir.basic_block_data_mut(bb); - - if let Some(ref mut term) = data.terminator { - let is_invoke = term_is_invoke(term); - let term_span = term.span; - let term_scope = term.scope; - let succs = term.successors_mut(); - if succs.len() > 1 || (succs.len() > 0 && is_invoke) { - for tgt in succs { - let num_preds = pred_count[tgt.index()]; - if num_preds > 1 { - // It's a critical edge, break it - let goto = Terminator { - span: term_span, - scope: term_scope, - kind: TerminatorKind::Goto { target: *tgt } - }; - let mut data = BasicBlockData::new(Some(goto)); - data.is_cleanup = cleanup_map.contains(tgt.index()); - - // Get the index it will be when inserted into the MIR - let idx = cur_len + new_blocks.len(); - new_blocks.push(data); - *tgt = BasicBlock::new(idx); - } - } - } - } - } - - debug!("Broke {} N edges", new_blocks.len()); - - mir.basic_blocks.extend_from_slice(&new_blocks); -} - -// Returns true if the terminator would use an invoke in LLVM. -fn term_is_invoke(term: &Terminator) -> bool { - match term.kind { - TerminatorKind::Call { cleanup: Some(_), .. } | - TerminatorKind::Drop { unwind: Some(_), .. } => true, - _ => false - } -} diff --git a/src/librustc_mir/transform/mod.rs b/src/librustc_mir/transform/mod.rs index 51f5c3cd7f5..0dcb7ef84d0 100644 --- a/src/librustc_mir/transform/mod.rs +++ b/src/librustc_mir/transform/mod.rs @@ -13,6 +13,6 @@ pub mod simplify_cfg; pub mod erase_regions; pub mod no_landing_pads; pub mod type_check; -pub mod break_critical_edges; +pub mod break_cleanup_edges; pub mod promote_consts; pub mod qualify_consts;