Auto merge of #30301 - michaelwoerister:mir-to-metadata2, r=nikomatsakis

This PR makes `Mir` `RustcEncodable` and `RustcDecodable` and stores it in crate metadata for inlinable items.

Some other things in here:
- `mir::visit::Visitor` is extended to also visit `Literals`, `Spans` and `DefIds`.
- It also adds `mir::visit::MutVisitor` which allows to mutate the visited `Mir` structure in place.
- Some numbers on how big MIR is in metadata (total metadata size in bytes):

|                | w/ MIR     | w/o MIR     | Rel. Size |
|----------------|-----------:|------------:|:---------:|
| libcore        | 17,695,473 |  14,263,377 |  124%     |
| liblibc        | 411,440   |  404,382    | 102%      |
| libcollections |  4,537,975 |   3,526,933 |   129%    |
| libserialize   |  2,574,769 |   2,060,798 |   125%    |
| libsyntax      | 15,262,894 |  12,075,574 |  126%     |
| librustc       | 16,984,537 |  13,692,168 |  124%     |

So, adding MIR to metadata makes it about 25% bigger. It could be worse, considering that it still uses the inefficient RBML encoding. Still, the question is whether we should put MIR emission behind a `-Z` flag.

Author: bors

src/librustc/middle/const_eval.rs

@@ -242,7 +242,7 @@ pub fn lookup_const_fn_by_id<'tcx>(tcx: &ty::ctxt<'tcx>, def_id: DefId)
     }
 }
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, RustcEncodable, RustcDecodable)]
 pub enum ConstVal {
     Float(f64),
     Int(i64),

src/librustc/middle/cstore.rs

@@ -28,6 +28,7 @@ use middle::def;
 use middle::lang_items;
 use middle::ty::{self, Ty};
 use middle::def_id::{DefId, DefIndex};
+use mir::repr::Mir;
 use session::Session;
 use session::search_paths::PathKind;
 use util::nodemap::{FnvHashMap, NodeMap, NodeSet};
@@ -100,6 +101,7 @@ pub enum InlinedItem {
 }
 
 /// A borrowed version of `hir::InlinedItem`.
+#[derive(Clone, Copy, PartialEq, Eq, Hash, Debug)]
 pub enum InlinedItemRef<'a> {
     Item(&'a hir::Item),
     TraitItem(DefId, &'a hir::TraitItem),
@@ -216,6 +218,8 @@ pub trait CrateStore<'tcx> : Any {
     // misc. metadata
     fn maybe_get_item_ast(&'tcx self, tcx: &ty::ctxt<'tcx>, def: DefId)
                           -> FoundAst<'tcx>;
+    fn maybe_get_item_mir(&self, tcx: &ty::ctxt<'tcx>, def: DefId)
+                          -> Option<Mir<'tcx>>;
     // This is basically a 1-based range of ints, which is a little
     // silly - I may fix that.
     fn crates(&self) -> Vec<ast::CrateNum>;
@@ -235,6 +239,7 @@ pub trait CrateStore<'tcx> : Any {
                        item_symbols: &RefCell<NodeMap<String>>,
                        link_meta: &LinkMeta,
                        reachable: &NodeSet,
+                       mir_map: &NodeMap<Mir<'tcx>>,
                        krate: &hir::Crate) -> Vec<u8>;
     fn metadata_encoding_version(&self) -> &[u8];
 }
@@ -383,6 +388,9 @@ impl<'tcx> CrateStore<'tcx> for DummyCrateStore {
     // misc. metadata
     fn maybe_get_item_ast(&'tcx self, tcx: &ty::ctxt<'tcx>, def: DefId)
                           -> FoundAst<'tcx> { unimplemented!() }
+    fn maybe_get_item_mir(&self, tcx: &ty::ctxt<'tcx>, def: DefId)
+                          -> Option<Mir<'tcx>> { unimplemented!() }
+
     // This is basically a 1-based range of ints, which is a little
     // silly - I may fix that.
     fn crates(&self) -> Vec<ast::CrateNum> { vec![] }
@@ -404,6 +412,7 @@ impl<'tcx> CrateStore<'tcx> for DummyCrateStore {
                        item_symbols: &RefCell<NodeMap<String>>,
                        link_meta: &LinkMeta,
                        reachable: &NodeSet,
+                       mir_map: &NodeMap<Mir<'tcx>>,
                        krate: &hir::Crate) -> Vec<u8> { vec![] }
     fn metadata_encoding_version(&self) -> &[u8] { unimplemented!() }
 }

src/librustc/middle/ty/sty.rs

@@ -10,6 +10,7 @@
 
 //! This module contains TypeVariants and its major components
 
+use middle::cstore;
 use middle::def_id::DefId;
 use middle::region;
 use middle::subst::{self, Substs};
@@ -26,6 +27,8 @@ use syntax::abi;
 use syntax::ast::{self, Name};
 use syntax::parse::token::special_idents;
 
+use serialize::{Decodable, Decoder};
+
 use rustc_front::hir;
 
 use self::FnOutput::*;
@@ -233,7 +236,7 @@ pub enum TypeVariants<'tcx> {
 /// closure C wind up influencing the decisions we ought to make for
 /// closure C (which would then require fixed point iteration to
 /// handle). Plus it fixes an ICE. :P
-#[derive(Clone, PartialEq, Eq, Hash, Debug)]
+#[derive(Clone, PartialEq, Eq, Hash, Debug, RustcEncodable, RustcDecodable)]
 pub struct ClosureSubsts<'tcx> {
     /// Lifetime and type parameters from the enclosing function.
     /// These are separated out because trans wants to pass them around
@@ -246,6 +249,23 @@ pub struct ClosureSubsts<'tcx> {
     pub upvar_tys: Vec<Ty<'tcx>>
 }
 
+impl<'tcx> Decodable for &'tcx ClosureSubsts<'tcx> {
+    fn decode<S: Decoder>(s: &mut S) -> Result<&'tcx ClosureSubsts<'tcx>, S::Error> {
+        let closure_substs = try! { Decodable::decode(s) };
+        let dummy_def_id: DefId = unsafe { mem::zeroed() };
+
+        cstore::tls::with_decoding_context(s, |dcx, _| {
+            // Intern the value
+            let ty = dcx.tcx().mk_closure_from_closure_substs(dummy_def_id,
+                                                              Box::new(closure_substs));
+            match ty.sty {
+                TyClosure(_, ref closure_substs) => Ok(&**closure_substs),
+                _ => unreachable!()
+            }
+        })
+    }
+}
+
 #[derive(Clone, PartialEq, Eq, Hash)]
 pub struct TraitTy<'tcx> {
     pub principal: ty::PolyTraitRef<'tcx>,
@@ -434,7 +454,7 @@ pub struct ClosureTy<'tcx> {
     pub sig: PolyFnSig<'tcx>,
 }
 
-#[derive(Clone, Copy, PartialEq, Eq, Hash, Debug)]
+#[derive(Clone, Copy, PartialEq, Eq, Hash, Debug, RustcEncodable, RustcDecodable)]
 pub enum FnOutput<'tcx> {
     FnConverging(Ty<'tcx>),
     FnDiverging
@@ -632,7 +652,7 @@ pub struct DebruijnIndex {
 ///
 /// [1] http://smallcultfollowing.com/babysteps/blog/2013/10/29/intermingled-parameter-lists/
 /// [2] http://smallcultfollowing.com/babysteps/blog/2013/11/04/intermingled-parameter-lists/
-#[derive(Clone, PartialEq, Eq, Hash, Copy)]
+#[derive(Clone, PartialEq, Eq, Hash, Copy, RustcEncodable, RustcDecodable)]
 pub enum Region {
     // Region bound in a type or fn declaration which will be
     // substituted 'early' -- that is, at the same time when type
@@ -701,7 +721,7 @@ pub struct RegionVid {
     pub index: u32
 }
 
-#[derive(Clone, Copy, PartialEq, Eq, Hash)]
+#[derive(Clone, Copy, PartialEq, Eq, Hash, RustcEncodable, RustcDecodable)]
 pub struct SkolemizedRegionVid {
     pub index: u32
 }