From c4fe96c3234a1e21b2d61fc3e6f28e6522ad7ab2 Mon Sep 17 00:00:00 2001 From: Camille GILLOT Date: Wed, 11 Jan 2023 16:30:35 +0000 Subject: [PATCH] Allow to remove unused definitions without renumbering locals. --- compiler/rustc_mir_transform/src/simplify.rs | 16 ++++++++++++++-- 1 file changed, 14 insertions(+), 2 deletions(-) diff --git a/compiler/rustc_mir_transform/src/simplify.rs b/compiler/rustc_mir_transform/src/simplify.rs index 8f6abe7a912..09b980bab29 100644 --- a/compiler/rustc_mir_transform/src/simplify.rs +++ b/compiler/rustc_mir_transform/src/simplify.rs @@ -404,6 +404,18 @@ impl<'tcx> MirPass<'tcx> for SimplifyLocals { } } +pub fn remove_unused_definitions<'tcx>(body: &mut Body<'tcx>) { + // First, we're going to get a count of *actual* uses for every `Local`. + let mut used_locals = UsedLocals::new(body); + + // Next, we're going to remove any `Local` with zero actual uses. When we remove those + // `Locals`, we're also going to subtract any uses of other `Locals` from the `used_locals` + // count. For example, if we removed `_2 = discriminant(_1)`, then we'll subtract one from + // `use_counts[_1]`. That in turn might make `_1` unused, so we loop until we hit a + // fixedpoint where there are no more unused locals. + remove_unused_definitions_helper(&mut used_locals, body); +} + pub fn simplify_locals<'tcx>(body: &mut Body<'tcx>, tcx: TyCtxt<'tcx>) { // First, we're going to get a count of *actual* uses for every `Local`. let mut used_locals = UsedLocals::new(body); @@ -413,7 +425,7 @@ pub fn simplify_locals<'tcx>(body: &mut Body<'tcx>, tcx: TyCtxt<'tcx>) { // count. For example, if we removed `_2 = discriminant(_1)`, then we'll subtract one from // `use_counts[_1]`. That in turn might make `_1` unused, so we loop until we hit a // fixedpoint where there are no more unused locals. - remove_unused_definitions(&mut used_locals, body); + remove_unused_definitions_helper(&mut used_locals, body); // Finally, we'll actually do the work of shrinking `body.local_decls` and remapping the `Local`s. let map = make_local_map(&mut body.local_decls, &used_locals); @@ -548,7 +560,7 @@ impl<'tcx> Visitor<'tcx> for UsedLocals { } /// Removes unused definitions. Updates the used locals to reflect the changes made. -fn remove_unused_definitions(used_locals: &mut UsedLocals, body: &mut Body<'_>) { +fn remove_unused_definitions_helper(used_locals: &mut UsedLocals, body: &mut Body<'_>) { // The use counts are updated as we remove the statements. A local might become unused // during the retain operation, leading to a temporary inconsistency (storage statements or // definitions referencing the local might remain). For correctness it is crucial that this