retool MIR passes completely

The new setup is as follows. There is a pipeline of MIR passes that each
run **per def-id** to optimize a particular function. You are intended
to request MIR at whatever stage you need it. At the moment, there is
only one stage you can request:

- `optimized_mir(def_id)`

This yields the final product. Internally, it pulls the MIR for the
given def-id through a series of steps. Right now, these are still using
an "interned ref-cell" but they are intended to "steal" from one
another:

- `mir_build` -- performs the initial construction for local MIR
- `mir_pass_set` -- performs a suite of optimizations and transformations
- `mir_pass` -- an individual optimization within a suite

So, to construct the optimized MIR, we invoke:

    mir_pass_set((MIR_OPTIMIZED, def_id))

which will build up the final MIR.

src/librustc/mir/transform.rs

@@ -9,13 +9,13 @@
 // except according to those terms.
 
 use hir;
-use hir::def_id::{DefId, LOCAL_CRATE};
+use hir::def_id::DefId;
 use hir::map::DefPathData;
 use mir::{Mir, Promoted};
 use ty::TyCtxt;
+use std::cell::{Ref, RefCell};
 use std::rc::Rc;
 use syntax::ast::NodeId;
-use util::common::time;
 
 use std::borrow::Cow;
 
@@ -90,12 +90,37 @@ pub fn default_name<T: ?Sized>() -> Cow<'static, str> {
     }
 }
 
+/// Gives you access to various bits of state during your MIR pass.
+pub trait MirCtxt<'a, 'tcx: 'a> {
+    fn tcx(&self) -> TyCtxt<'a, 'tcx, 'tcx>;
+    fn def_id(&self) -> DefId;
+    fn pass_set(&self) -> MirPassSet;
+    fn pass_num(&self) -> MirPassIndex;
+    fn source(&self) -> MirSource;
+    fn read_previous_mir(&self) -> Ref<'tcx, Mir<'tcx>>;
+    fn steal_previous_mir(&self) -> &'tcx RefCell<Mir<'tcx>>;
+}
+
+#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, PartialOrd, Ord)]
+pub struct MirPassSet(pub usize);
+
+#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, PartialOrd, Ord)]
+pub struct MirPassIndex(pub usize);
+
+/// A pass hook is invoked both before and after each pass executes.
+/// This is primarily used to dump MIR for debugging.
+///
+/// You can tell whether this is before or after by inspecting the
+/// `mir` parameter -- before the pass executes, it will be `None` (in
+/// which case you can inspect the MIR from previous pass by executing
+/// `mir_cx.read_previous_mir()`); after the pass executes, it will be
+/// `Some()` with the result of the pass (in which case the output
+/// from the previous pass is most likely stolen, so you would not
+/// want to try and access it).
 pub trait PassHook {
-    fn on_mir_pass<'a, 'tcx>(&self,
-                             tcx: TyCtxt<'a, 'tcx, 'tcx>,
-                             pass_name: &str,
-                             pass_num: usize,
-                             is_after: bool);
+    fn on_mir_pass<'a, 'tcx: 'a>(&self,
+                                 mir_cx: &MirCtxt<'a, 'tcx>,
+                                 mir: Option<&Mir<'tcx>>);
 }
 
 /// A streamlined trait that you can implement to create a pass; the
@@ -107,21 +132,7 @@ pub trait DefIdPass {
         default_name::<Self>()
     }
 
-    fn run_pass<'a, 'tcx>(&self,
-                          tcx: TyCtxt<'a, 'tcx, 'tcx>,
-                          def_id: DefId);
-}
-
-impl<T: DefIdPass> Pass for T {
-    fn name<'a>(&'a self) -> Cow<'a, str> {
-        DefIdPass::name(self)
-    }
-
-    fn run_pass<'a, 'tcx>(&self, tcx: TyCtxt<'a, 'tcx, 'tcx>) {
-        for &def_id in tcx.mir_keys(LOCAL_CRATE).iter() {
-            DefIdPass::run_pass(self, tcx, def_id);
-        }
-    }
+    fn run_pass<'a, 'tcx: 'a>(&self, mir_cx: &MirCtxt<'a, 'tcx>) -> &'tcx RefCell<Mir<'tcx>>;
 }
 
 /// A streamlined trait that you can implement to create a pass; the
@@ -138,29 +149,24 @@ pub trait MirPass: DepGraphSafe {
                           mir: &mut Mir<'tcx>);
 }
 
-fn for_each_assoc_mir<'a, 'tcx, OP>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
-                                    def_id: DefId,
-                                    mut op: OP)
-    where OP: FnMut(MirSource, &mut Mir<'tcx>)
-{
-    let id = tcx.hir.as_local_node_id(def_id).expect("mir source requires local def-id");
-    let source = MirSource::from_node(tcx, id);
-    let mir = &mut tcx.mir(def_id).borrow_mut();
-    op(source, mir);
-
-    for (promoted_index, promoted_mir) in mir.promoted.iter_enumerated_mut() {
-        let promoted_source = MirSource::Promoted(id, promoted_index);
-        op(promoted_source, promoted_mir);
-    }
-}
-
 impl<T: MirPass> DefIdPass for T {
     fn name<'a>(&'a self) -> Cow<'a, str> {
         MirPass::name(self)
     }
 
-    fn run_pass<'a, 'tcx>(&self, tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId) {
-        for_each_assoc_mir(tcx, def_id, |src, mir| MirPass::run_pass(self, tcx, src, mir));
+    fn run_pass<'a, 'tcx: 'a>(&self, mir_cx: &MirCtxt<'a, 'tcx>) -> &'tcx RefCell<Mir<'tcx>> {
+        let tcx = mir_cx.tcx();
+        let source = mir_cx.source();
+        let mir = mir_cx.steal_previous_mir();
+        MirPass::run_pass(self, tcx, source, &mut mir.borrow_mut());
+
+        let item_id = source.item_id();
+        for (promoted_index, promoted_mir) in mir.borrow_mut().promoted.iter_enumerated_mut() {
+            let promoted_source = MirSource::Promoted(item_id, promoted_index);
+            MirPass::run_pass(self, tcx, promoted_source, promoted_mir);
+        }
+
+        mir
     }
 }
 
@@ -168,12 +174,7 @@ impl<T: MirPass> DefIdPass for T {
 #[derive(Clone)]
 pub struct Passes {
     pass_hooks: Vec<Rc<PassHook>>,
-    sets: Vec<PassSet>,
-}
-
-#[derive(Clone)]
-struct PassSet {
-    passes: Vec<Rc<DefIdPass>>,
+    sets: Vec<Vec<Rc<DefIdPass>>>,
 }
 
 /// The number of "pass sets" that we have:
@@ -184,52 +185,41 @@ struct PassSet {
 pub const MIR_PASS_SETS: usize = 3;
 
 /// Run the passes we need to do constant qualification and evaluation.
-pub const MIR_CONST: usize = 0;
+pub const MIR_CONST: MirPassSet = MirPassSet(0);
 
 /// Run the passes we need to consider the MIR validated and ready for borrowck etc.
-pub const MIR_VALIDATED: usize = 1;
+pub const MIR_VALIDATED: MirPassSet = MirPassSet(1);
 
 /// Run the passes we need to consider the MIR *optimized*.
-pub const MIR_OPTIMIZED: usize = 2;
+pub const MIR_OPTIMIZED: MirPassSet = MirPassSet(2);
 
 impl<'a, 'tcx> Passes {
     pub fn new() -> Passes {
         Passes {
             pass_hooks: Vec::new(),
-            sets: (0..MIR_PASS_SETS).map(|_| PassSet { passes: Vec::new() }).collect(),
-        }
-    }
-
-    pub fn run_passes(&self, tcx: TyCtxt<'a, 'tcx, 'tcx>, set_index: usize) {
-        let set = &self.sets[set_index];
-
-        let start_num: usize = self.sets[..set_index].iter().map(|s| s.passes.len()).sum();
-
-        // NB: passes are numbered from 1, since "construction" is zero.
-        for (pass, pass_num) in set.passes.iter().zip(start_num + 1..) {
-            for hook in &self.pass_hooks {
-                hook.on_mir_pass(tcx, &pass.name(), pass_num, false);
-            }
-
-            time(tcx.sess.time_passes(), &*pass.name(), || {
-                for &def_id in tcx.mir_keys(LOCAL_CRATE).iter() {
-                    pass.run_pass(tcx, def_id);
-                }
-            });
-
-            for hook in &self.pass_hooks {
-                hook.on_mir_pass(tcx, &pass.name(), pass_num, true);
-            }
+            sets: (0..MIR_PASS_SETS).map(|_| Vec::new()).collect(),
         }
     }
 
     /// Pushes a built-in pass.
-    pub fn push_pass<T: DefIdPass + 'static>(&mut self, set: usize, pass: T) {
-        self.sets[set].passes.push(Rc::new(pass));
+    pub fn push_pass<T: DefIdPass + 'static>(&mut self, set: MirPassSet, pass: T) {
+        self.sets[set.0].push(Rc::new(pass));
     }
 
     /// Pushes a pass hook.
     pub fn push_hook<T: PassHook + 'static>(&mut self, hook: T) {
         self.pass_hooks.push(Rc::new(hook));
     }
+
+    pub fn len_passes(&self, set: MirPassSet) -> usize {
+        self.sets[set.0].len()
+    }
+
+    pub fn pass(&self, set: MirPassSet, pass: MirPassIndex) -> &DefIdPass {
+        &*self.sets[set.0][pass.0]
+    }
+
+    pub fn hooks(&self) -> &[Rc<PassHook>] {
+        &self.pass_hooks
+    }
 }

src/librustc/ty/maps.rs

@@ -16,6 +16,7 @@ use middle::const_val;
 use middle::privacy::AccessLevels;
 use middle::region::RegionMaps;
 use mir;
+use mir::transform::{MirPassSet, MirPassIndex};
 use session::CompileResult;
 use ty::{self, CrateInherentImpls, Ty, TyCtxt};
 use ty::item_path;
@@ -101,6 +102,24 @@ impl<'tcx> Key for (DefId, &'tcx Substs<'tcx>) {
     }
 }
 
+impl Key for (MirPassSet, DefId) {
+    fn map_crate(&self) -> CrateNum {
+        self.1.map_crate()
+    }
+    fn default_span(&self, tcx: TyCtxt) -> Span {
+        self.1.default_span(tcx)
+    }
+}
+
+impl Key for (MirPassSet, MirPassIndex, DefId) {
+    fn map_crate(&self) -> CrateNum {
+        self.2.map_crate()
+    }
+    fn default_span(&self, tcx: TyCtxt) -> Span {
+        self.2.default_span(tcx)
+    }
+}
+
 trait Value<'tcx>: Sized {
     fn from_cycle_error<'a>(tcx: TyCtxt<'a, 'tcx, 'tcx>) -> Self;
 }
@@ -318,6 +337,18 @@ impl<'tcx> QueryDescription for queries::is_item_mir_available<'tcx> {
     }
 }
 
+impl<'tcx> QueryDescription for queries::mir_pass_set<'tcx> {
+    fn describe(_: TyCtxt, (pass_set, _): (MirPassSet, DefId)) -> String {
+        format!("MIR passes #{}.*", pass_set.0)
+    }
+}
+
+impl<'tcx> QueryDescription for queries::mir_pass<'tcx> {
+    fn describe(_: TyCtxt, (pass_set, pass_num, _): (MirPassSet, MirPassIndex, DefId)) -> String {
+        format!("MIR pass #{}.{}", pass_set.0, pass_num.0)
+    }
+}
+
 macro_rules! define_maps {
     (<$tcx:tt>
      $($(#[$attr:meta])*
@@ -542,15 +573,6 @@ define_maps! { <'tcx>
     /// Methods in these implementations don't need to be exported.
     [] inherent_impls: InherentImpls(DefId) -> Rc<Vec<DefId>>,
 
-    /// Maps from the def-id of a function/method or const/static
-    /// to its MIR. Mutation is done at an item granularity to
-    /// allow MIR optimization passes to function and still
-    /// access cross-crate MIR (e.g. inlining or const eval).
-    ///
-    /// Note that cross-crate MIR appears to be always borrowed
-    /// (in the `RefCell` sense) to prevent accidental mutation.
-    [] mir: Mir(DefId) -> &'tcx RefCell<mir::Mir<'tcx>>,
-
     /// Set of all the def-ids in this crate that have MIR associated with
     /// them. This includes all the body owners, but also things like struct
     /// constructors.
@@ -561,6 +583,26 @@ define_maps! { <'tcx>
     /// the value isn't known except to the pass itself.
     [] mir_const_qualif: Mir(DefId) -> u8,
 
+    /// Performs the initial MIR construction. You almost certainly do not
+    /// want to use this query, because its output is intended to be stolen
+    /// immediately by the MIR passes below. Consider `optimized_mir` instead.
+    [] mir_build: Mir(DefId) -> &'tcx RefCell<mir::Mir<'tcx>>,
+
+    /// Fetch the MIR for a given def-id after the given set of passes has ben
+    /// applied to it. This is mostly an "intermediate" query. Normally, you would
+    /// prefer to use `optimized_mir(def_id)`, which will fetch the MIR after all
+    /// optimizations and so forth.
+    [] mir_pass_set: mir_pass_set((MirPassSet, DefId)) -> &'tcx RefCell<mir::Mir<'tcx>>,
+
+    /// Fetch the MIR for a given def-id after a given pass has been executed. This is
+    /// **only** intended to be used by the `mir_pass_set` provider -- if you are using it
+    /// manually, you're doing it wrong.
+    [] mir_pass: mir_pass((MirPassSet, MirPassIndex, DefId)) -> &'tcx RefCell<mir::Mir<'tcx>>,
+
+    /// MIR after our optimization passes have run. This is MIR that is ready
+    /// for trans. This is also the only query that can fetch non-local MIR, at present.
+    [] optimized_mir: Mir(DefId) -> &'tcx RefCell<mir::Mir<'tcx>>,
+
     /// Records the type of each closure. The def ID is the ID of the
     /// expression defining the closure.
     [] closure_kind: ItemSignature(DefId) -> ty::ClosureKind,
@@ -658,3 +700,11 @@ fn const_eval_dep_node((def_id, _): (DefId, &Substs)) -> DepNode<DefId> {
 fn mir_keys(_: CrateNum) -> DepNode<DefId> {
     DepNode::MirKeys
 }
+
+fn mir_pass_set((_pass_set, def_id): (MirPassSet, DefId)) -> DepNode<DefId> {
+    DepNode::Mir(def_id)
+}
+
+fn mir_pass((_pass_set, _pass_num, def_id): (MirPassSet, MirPassIndex, DefId)) -> DepNode<DefId> {
+    DepNode::Mir(def_id)
+}

src/librustc/ty/mod.rs

@@ -2323,9 +2323,9 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
         }
     }
 
-    /// Given the did of an item, returns its MIR, borrowed immutably.
+    /// Given the did of an item, returns its (optimized) MIR, borrowed immutably.
     pub fn item_mir(self, did: DefId) -> Ref<'gcx, Mir<'gcx>> {
-        self.mir(did).borrow()
+        self.optimized_mir(did).borrow()
     }
 
     /// Return the possibly-auto-generated MIR of a (DefId, Subst) pair.
@@ -2333,8 +2333,16 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
                         -> Ref<'gcx, Mir<'gcx>>
     {
         match instance {
-            ty::InstanceDef::Item(did) if true => self.item_mir(did),
-            _ => self.mir_shims(instance).borrow(),
+            ty::InstanceDef::Item(did) => {
+                self.item_mir(did)
+            }
+            ty::InstanceDef::Intrinsic(..) |
+            ty::InstanceDef::FnPtrShim(..) |
+            ty::InstanceDef::Virtual(..) |
+            ty::InstanceDef::ClosureOnceShim { .. } |
+            ty::InstanceDef::DropGlue(..) => {
+                self.mir_shims(instance).borrow()
+            }
         }
     }