librustc_mir: Remove &*x when x has a reference type.
#36504
Conversation
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This should open up some new copy prop opportunities. |
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Does this include |
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@cbreeden No, that's somewhat more complex because it's not self-contained within a statement. |
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How's this? |
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| struct OptimizationList { | ||
| and_stars: HashSet<Location>, |
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Should use FnvHashSet (from rustc::utils::nodemap) in the compiler.
| } | ||
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| impl OptimizationList { | ||
| fn new() -> OptimizationList { |
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This can be done via #[derive(Default)].
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| impl<'tcx> MutVisitor<'tcx> for InstCombine { | ||
| fn visit_rvalue(&mut self, rvalue: &mut Rvalue<'tcx>, location: Location) { | ||
| if self.optimizations.and_stars.contains(&location) { |
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Can use remove instead of contains to do both at once.
| debug!("Replacing `&*`: {:?}", rvalue); | ||
| let new_lvalue = match *rvalue { | ||
| Rvalue::Ref(_, _, Lvalue::Projection(ref mut projection)) => { | ||
| mem::replace(&mut projection.base, Lvalue::ReturnPointer) |
| Rvalue::Ref(_, _, Lvalue::Projection(ref mut projection)) => { | ||
| mem::replace(&mut projection.base, Lvalue::ReturnPointer) | ||
| } | ||
| _ => panic!("Detected `&*` but didn't find `&*`!"), |
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Updated. r? @eddyb |
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@bors r+ |
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📌 Commit 11a4965 has been approved by |
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@bors r- This will cause drop elaboration to crash and burn, because the newly-created code moves behind |
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Ah, right, my bad, I forgot that it had to go after drop elaboration. We need more comments in the pass list. |
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I would like to have more understanding on what properties MIR must have at every step before we start doing destructive optimizations. |
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@arielb1 Right now we are generating very bad code. I think it would be unwise to gate needed optimizations on "understanding of what properties MIR must have at every step". We need these optimizations now. As long as everything works, we can do that later. |
| @@ -1019,6 +1019,7 @@ pub fn phase_4_translate_to_llvm<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, | |||
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| passes.push_pass(box mir::transform::erase_regions::EraseRegions); | |||
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| passes.push_pass(box mir::transform::instcombine::InstCombine::new()); | |||
| passes.push_pass(box mir::transform::add_call_guards::AddCallGuards); | |||
| passes.push_pass(box borrowck::ElaborateDrops); | |||
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You only need to reorder the pass to go after this line, which should be separated and commented.
This is the point where moves stop existing and you only have raw semantic-less copies.
This introduces a new `InstCombine` pass for us to place such peephole optimizations.
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@bors-servo: r=eddyb |
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📌 Commit e8a44d2 has been approved by |
librustc_mir: Remove `&*x` when `x` has a reference type. This introduces a new `InstCombine` pass for us to place such peephole optimizations. r? @eddyb
librustc_mir: Remove `&*x` when `x` has a reference type. This introduces a new `InstCombine` pass for us to place such peephole optimizations. r? @eddyb
This introduces a new
InstCombinepass for us to place such peepholeoptimizations.
r? @eddyb