Move BottomValue into framework/mod.rs

Author: ecstatic-morse

src/librustc_mir/dataflow/framework/mod.rs

@@ -41,8 +41,6 @@ use rustc_hir::def_id::DefId;
 use rustc_index::bit_set::{BitSet, HybridBitSet};
 use rustc_index::vec::{Idx, IndexVec};
 
-use crate::dataflow::BottomValue;
-
 mod cursor;
 mod engine;
 mod graphviz;
@@ -95,6 +93,47 @@ where
     }
 }
 
+/// Parameterization for the precise form of data flow that is used.
+///
+/// `BottomValue` determines whether the initial entry set for each basic block is empty or full.
+/// This also determines the semantics of the lattice `join` operator used to merge dataflow
+/// results, since dataflow works by starting at the bottom and moving monotonically to a fixed
+/// point.
+///
+/// This means, for propagation across the graph, that you either want to start at all-zeroes and
+/// then use Union as your merge when propagating, or you start at all-ones and then use Intersect
+/// as your merge when propagating.
+pub trait BottomValue {
+    /// Specifies the initial value for each bit in the entry set for each basic block.
+    const BOTTOM_VALUE: bool;
+
+    /// Merges `in_set` into `inout_set`, returning `true` if `inout_set` changed.
+    ///
+    /// It is almost certainly wrong to override this, since it automatically applies
+    /// * `inout_set & in_set` if `BOTTOM_VALUE == true`
+    /// * `inout_set | in_set` if `BOTTOM_VALUE == false`
+    ///
+    /// This means that if a bit is not `BOTTOM_VALUE`, it is propagated into all target blocks.
+    /// For clarity, the above statement again from a different perspective:
+    /// A bit in the block's entry set is `!BOTTOM_VALUE` if *any* predecessor block's bit value is
+    /// `!BOTTOM_VALUE`.
+    ///
+    /// There are situations where you want the opposite behaviour: propagate only if *all*
+    /// predecessor blocks's value is `!BOTTOM_VALUE`.
+    /// E.g. if you want to know whether a bit is *definitely* set at a specific location. This
+    /// means that all code paths leading to the location must have set the bit, instead of any
+    /// code path leading there.
+    ///
+    /// If you want this kind of "definitely set" analysis, you need to
+    /// 1. Invert `BOTTOM_VALUE`
+    /// 2. Reset the `entry_set` in `start_block_effect` to `!BOTTOM_VALUE`
+    /// 3. Override `join` to do the opposite from what it's doing now.
+    #[inline]
+    fn join<T: Idx>(&self, inout_set: &mut BitSet<T>, in_set: &BitSet<T>) -> bool {
+        if !Self::BOTTOM_VALUE { inout_set.union(in_set) } else { inout_set.intersect(in_set) }
+    }
+}
+
 /// Define the domain of a dataflow problem.
 ///
 /// This trait specifies the lattice on which this analysis operates. For now, this must be a

src/librustc_mir/dataflow/mod.rs

@@ -1,13 +1,11 @@
 use rustc::ty;
 use rustc_ast::ast::{self, MetaItem};
-use rustc_index::bit_set::BitSet;
-use rustc_index::vec::Idx;
 use rustc_span::symbol::{sym, Symbol};
 
 pub(crate) use self::drop_flag_effects::*;
 pub use self::framework::{
-    visit_results, Analysis, AnalysisDomain, BorrowckFlowState, BorrowckResults, Engine, GenKill,
-    GenKillAnalysis, Results, ResultsCursor, ResultsRefCursor, ResultsVisitor,
+    visit_results, Analysis, AnalysisDomain, BorrowckFlowState, BorrowckResults, BottomValue,
+    Engine, GenKill, GenKillAnalysis, Results, ResultsCursor, ResultsRefCursor, ResultsVisitor,
 };
 pub use self::impls::{
     borrows::Borrows, DefinitelyInitializedPlaces, EverInitializedPlaces, MaybeBorrowedLocals,
@@ -48,44 +46,3 @@ pub(crate) fn has_rustc_mir_with(attrs: &[ast::Attribute], name: Symbol) -> Opti
     }
     None
 }
-
-/// Parameterization for the precise form of data flow that is used.
-///
-/// `BottomValue` determines whether the initial entry set for each basic block is empty or full.
-/// This also determines the semantics of the lattice `join` operator used to merge dataflow
-/// results, since dataflow works by starting at the bottom and moving monotonically to a fixed
-/// point.
-///
-/// This means, for propagation across the graph, that you either want to start at all-zeroes and
-/// then use Union as your merge when propagating, or you start at all-ones and then use Intersect
-/// as your merge when propagating.
-pub trait BottomValue {
-    /// Specifies the initial value for each bit in the entry set for each basic block.
-    const BOTTOM_VALUE: bool;
-
-    /// Merges `in_set` into `inout_set`, returning `true` if `inout_set` changed.
-    ///
-    /// It is almost certainly wrong to override this, since it automatically applies
-    /// * `inout_set & in_set` if `BOTTOM_VALUE == true`
-    /// * `inout_set | in_set` if `BOTTOM_VALUE == false`
-    ///
-    /// This means that if a bit is not `BOTTOM_VALUE`, it is propagated into all target blocks.
-    /// For clarity, the above statement again from a different perspective:
-    /// A bit in the block's entry set is `!BOTTOM_VALUE` if *any* predecessor block's bit value is
-    /// `!BOTTOM_VALUE`.
-    ///
-    /// There are situations where you want the opposite behaviour: propagate only if *all*
-    /// predecessor blocks's value is `!BOTTOM_VALUE`.
-    /// E.g. if you want to know whether a bit is *definitely* set at a specific location. This
-    /// means that all code paths leading to the location must have set the bit, instead of any
-    /// code path leading there.
-    ///
-    /// If you want this kind of "definitely set" analysis, you need to
-    /// 1. Invert `BOTTOM_VALUE`
-    /// 2. Reset the `entry_set` in `start_block_effect` to `!BOTTOM_VALUE`
-    /// 3. Override `join` to do the opposite from what it's doing now.
-    #[inline]
-    fn join<T: Idx>(&self, inout_set: &mut BitSet<T>, in_set: &BitSet<T>) -> bool {
-        if !Self::BOTTOM_VALUE { inout_set.union(in_set) } else { inout_set.intersect(in_set) }
-    }
-}