Rename IdxSet::clone_from
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The current situation is something of a mess. - `IdxSetBuf` derefs to `IdxSet`. - `IdxSetBuf` implements `Clone`, and therefore has a provided `clone_from` method, which does allocation and so is expensive. - `IdxSet` has a `clone_from` method that is non-allocating and therefore cheap, but this method is not from the `Clone` trait. As a result, if you have an `IdxSetBuf` called `b`, if you call `b.clone_from(b2)` you'll get the expensive `IdxSetBuf` method, but if you call `(*b).clone_from(b2)` you'll get the cheap `IdxSetBuf` method. `liveness_of_locals()` does the former, presumably unintentionally, and therefore does lots of unnecessary allocations. Having a `clone_from` method that isn't from the `Clone` trait is a bad idea in general, so this patch renames it as `overwrite`. This avoids the unnecessary allocations in `liveness_of_locals()`, speeding up most NLL benchmarks, the best by 1.5%. It also means that calls of the form `(*b).clone_from(b2)` can be rewritten as `b.overwrite(b2)`.
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@ -233,7 +233,9 @@ impl<T: Idx> IdxSet<T> {
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&mut self.bits
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}
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pub fn clone_from(&mut self, other: &IdxSet<T>) {
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/// Efficiently overwrite `self` with `other`. Panics if `self` and `other`
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/// don't have the same length.
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pub fn overwrite(&mut self, other: &IdxSet<T>) {
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self.words_mut().clone_from_slice(other.words());
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}
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@ -139,7 +139,7 @@ impl<BD> FlowsAtLocation for FlowAtLocation<BD>
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where BD: BitDenotation
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{
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fn reset_to_entry_of(&mut self, bb: BasicBlock) {
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(*self.curr_state).clone_from(self.base_results.sets().on_entry_set_for(bb.index()));
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self.curr_state.overwrite(self.base_results.sets().on_entry_set_for(bb.index()));
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}
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fn reconstruct_statement_effect(&mut self, loc: Location) {
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@ -242,7 +242,7 @@ impl<'b, 'a: 'b, 'tcx: 'a, BD> PropagationContext<'b, 'a, 'tcx, BD> where BD: Bi
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{
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let sets = builder.flow_state.sets.for_block(bb_idx);
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debug_assert!(in_out.words().len() == sets.on_entry.words().len());
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in_out.clone_from(sets.on_entry);
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in_out.overwrite(sets.on_entry);
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in_out.union(sets.gen_set);
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in_out.subtract(sets.kill_set);
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}
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@ -141,14 +141,14 @@ pub fn liveness_of_locals<'tcx>(mir: &Mir<'tcx>, mode: LivenessMode) -> Liveness
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for &successor in mir.basic_blocks()[b].terminator().successors() {
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bits.union(&ins[successor]);
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}
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outs[b].clone_from(&bits);
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outs[b].overwrite(&bits);
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// bits = use ∪ (bits - def)
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def_use[b].apply(&mut bits);
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// update bits on entry and flag if they have changed
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if ins[b] != bits {
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ins[b].clone_from(&bits);
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ins[b].overwrite(&bits);
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changed = true;
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}
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}
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