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Auto merge of #68551 - Marwes:allocations_mir, r=ecstatic-morse

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perf: Reuse a Vec in mir simplification

Just moves the vec out of the outer loop so it is reused every iteration
This commit is contained in:
bors 2020-03-12 09:16:53 +00:00
commit 23de8275c9
1 changed files with 23 additions and 7 deletions
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30
src/librustc_mir/transform/simplify.rs
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@ -95,6 +95,11 @@ impl<'a, 'tcx> CfgSimplifier<'a, 'tcx> {
let mut start = START_BLOCK;
// Vec of the blocks that should be merged. We store the indices here, instead of the
// statements itself to avoid moving the (relatively) large statements twice.
// We do not push the statements directly into the target block (`bb`) as that is slower
// due to additional reallocations
let mut merged_blocks = Vec::new();
loop {
let mut changed = false;
@ -114,18 +119,28 @@ impl<'a, 'tcx> CfgSimplifier<'a, 'tcx> {
self.collapse_goto_chain(successor, &mut changed);
}
let mut new_stmts = vec![];
let mut inner_changed = true;
merged_blocks.clear();
while inner_changed {
inner_changed = false;
inner_changed |= self.simplify_branch(&mut terminator);
inner_changed |= self.merge_successor(&mut new_stmts, &mut terminator);
inner_changed |= self.merge_successor(&mut merged_blocks, &mut terminator);
changed |= inner_changed;
}
let data = &mut self.basic_blocks[bb];
data.statements.extend(new_stmts);
data.terminator = Some(terminator);
let statements_to_merge =
merged_blocks.iter().map(|&i| self.basic_blocks[i].statements.len()).sum();
if statements_to_merge > 0 {
let mut statements = std::mem::take(&mut self.basic_blocks[bb].statements);
statements.reserve(statements_to_merge);
for &from in &merged_blocks {
statements.append(&mut self.basic_blocks[from].statements);
}
self.basic_blocks[bb].statements = statements;
}
self.basic_blocks[bb].terminator = Some(terminator);
changed |= inner_changed;
}
@ -199,7 +214,7 @@ impl<'a, 'tcx> CfgSimplifier<'a, 'tcx> {
// merge a block with 1 `goto` predecessor to its parent
fn merge_successor(
&mut self,
new_stmts: &mut Vec<Statement<'tcx>>,
merged_blocks: &mut Vec<BasicBlock>,
terminator: &mut Terminator<'tcx>,
) -> bool {
let target = match terminator.kind {
@ -216,7 +231,8 @@ impl<'a, 'tcx> CfgSimplifier<'a, 'tcx> {
return false;
}
};
new_stmts.extend(self.basic_blocks[target].statements.drain(..));
merged_blocks.push(target);
self.pred_count[target] = 0;
true