Auto merge of #111396 - vlad20012:reduce-Borrows-dataflow-bitset-size, r=cjgillot

bors · bors · commit 4a59ba4d54a3 · 2023-05-12T17:37:05.000Z
Reduce BitSet size used in `Borrows` dataflow analysis

It looks like it is not needed to multiply the number of borrows by 2. Bits greater than `self.borrow_set.len()` are never set in this bitset. This should decrease the memory usage by an epsilon.
diff --git a/compiler/rustc_borrowck/src/dataflow.rs b/compiler/rustc_borrowck/src/dataflow.rs
@@ -328,7 +328,7 @@ impl<'tcx> rustc_mir_dataflow::AnalysisDomain<'tcx> for Borrows<'_, 'tcx> {
 
     fn bottom_value(&self, _: &mir::Body<'tcx>) -> Self::Domain {
         // bottom = nothing is reserved or activated yet;
-        BitSet::new_empty(self.borrow_set.len() * 2)
+        BitSet::new_empty(self.borrow_set.len())
     }
 
     fn initialize_start_block(&self, _: &mir::Body<'tcx>, _: &mut Self::Domain) {

Original file line number	Diff line number	Diff line change
`@@ -328,7 +328,7 @@ impl<'tcx> rustc_mir_dataflow::AnalysisDomain<'tcx> for Borrows<'_, 'tcx> {`
`328`	`328`
`329`	`329`	`fn bottom_value(&self, _: &mir::Body<'tcx>) -> Self::Domain {`
`330`	`330`	`// bottom = nothing is reserved or activated yet;`
`331`		`- BitSet::new_empty(self.borrow_set.len() * 2)`
	`331`	`+ BitSet::new_empty(self.borrow_set.len())`
`332`	`332`	`}`
`333`	`333`
`334`	`334`	`fn initialize_start_block(&self, _: &mir::Body<'tcx>, _: &mut Self::Domain) {`