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perf(mir): Reserve enough space for the merged blocks before appending

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This commit is contained in:
Markus Westerlind 2020-02-13 11:44:12 +01:00
parent 33513fad80
commit 2440998666
1 changed files with 17 additions and 4 deletions
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21
src/librustc_mir/transform/simplify.rs
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@ -95,6 +95,7 @@ pub fn simplify(mut self) {
let mut start = START_BLOCK;
let mut merged_blocks = Vec::new();
loop {
let mut changed = false;
@ -118,10 +119,23 @@ pub fn simplify(mut self) {
while inner_changed {
inner_changed = false;
inner_changed |= self.simplify_branch(&mut terminator);
inner_changed |= self.merge_successor(bb, &mut terminator);
inner_changed |= self.merge_successor(&mut merged_blocks, &mut terminator);
changed |= inner_changed;
}
let merged_block_count =
merged_blocks.iter().map(|&i| self.basic_blocks[i].statements.len()).sum();
if merged_block_count > 0 {
let mut statements = std::mem::take(&mut self.basic_blocks[bb].statements);
statements.reserve(merged_block_count);
for &from in &merged_blocks {
statements.append(&mut self.basic_blocks[from].statements);
}
self.basic_blocks[bb].statements = statements;
}
merged_blocks.clear();
self.basic_blocks[bb].terminator = Some(terminator);
changed |= inner_changed;
@ -196,7 +210,7 @@ fn collapse_goto_chain(&mut self, start: &mut BasicBlock, changed: &mut bool) {
// merge a block with 1 `goto` predecessor to its parent
fn merge_successor(
&mut self,
merge_into: BasicBlock,
merged_blocks: &mut Vec<BasicBlock>,
terminator: &mut Terminator<'tcx>,
) -> bool {
let target = match terminator.kind {
@ -214,8 +228,7 @@ fn merge_successor(
}
};
let (from, to) = self.basic_blocks.pick2_mut(target, merge_into);
to.statements.append(&mut from.statements);
merged_blocks.push(target);
self.pred_count[target] = 0;
true