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enhance ConstGoto mir-opt by moving up StorageDead statements

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SparrowLii 2022-04-06 15:17:41 +08:00
parent bbe9d27b8f
commit a91b347768
5 changed files with 167 additions and 127 deletions
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25
compiler/rustc_mir_transform/src/const_goto.rs
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@ -39,7 +39,9 @@ impl<'tcx> MirPass<'tcx> for ConstGoto {
opt_finder.visit_body(body);
let should_simplify = !opt_finder.optimizations.is_empty();
for opt in opt_finder.optimizations {
let terminator = body.basic_blocks_mut()[opt.bb_with_goto].terminator_mut();
let block = &mut body.basic_blocks_mut()[opt.bb_with_goto];
block.statements.extend(opt.stmts_move_up);
let terminator = block.terminator_mut();
let new_goto = TerminatorKind::Goto { target: opt.target_to_use_in_goto };
debug!("SUCCESS: replacing `{:?}` with `{:?}`", terminator.kind, new_goto);
terminator.kind = new_goto;
@ -68,12 +70,15 @@ impl<'tcx> Visitor<'tcx> for ConstGotoOptimizationFinder<'_, 'tcx> {
// Now check that the target of this Goto switches on this place.
let target_bb = &self.body.basic_blocks()[target];
// FIXME(simonvandel): We are conservative here when we don't allow
// any statements in the target basic block.
// This could probably be relaxed to allow `StorageDead`s which could be
// copied to the predecessor of this block.
if !target_bb.statements.is_empty() {
None?
// The `StorageDead(..)` statement does not affect the functionality of mir.
// We can move this part of the statement up to the predecessor.
let mut stmts_move_up = Vec::new();
for stmt in &target_bb.statements {
if let StatementKind::StorageDead(..) = stmt.kind {
stmts_move_up.push(stmt.clone())
} else {
None?;
}
}
let target_bb_terminator = target_bb.terminator();
@ -87,6 +92,7 @@ impl<'tcx> Visitor<'tcx> for ConstGotoOptimizationFinder<'_, 'tcx> {
self.optimizations.push(OptimizationToApply {
bb_with_goto: location.block,
target_to_use_in_goto,
stmts_move_up,
});
}
}
@ -97,14 +103,15 @@ impl<'tcx> Visitor<'tcx> for ConstGotoOptimizationFinder<'_, 'tcx> {
}
}
struct OptimizationToApply {
struct OptimizationToApply<'tcx> {
bb_with_goto: BasicBlock,
target_to_use_in_goto: BasicBlock,
stmts_move_up: Vec<Statement<'tcx>>,
}
pub struct ConstGotoOptimizationFinder<'a, 'tcx> {
tcx: TyCtxt<'tcx>,
body: &'a Body<'tcx>,
param_env: ParamEnv<'tcx>,
optimizations: Vec<OptimizationToApply>,
optimizations: Vec<OptimizationToApply<'tcx>>,
}