Auto merge of #46882 - oli-obk:miri3, r=eddyb

Replace all const evaluation with miri

* error reporting in constants prints a stacktrace through all called const fns
* Trivial constant propagation and folding in MIR (always active, irrelevant of the optimization level)
* can now use floating constants in patterns (previously only floating point literals were allowed)
    * the future compat lint is still produced for both cases
* can index into constant arrays during const eval (previously feature gated)
* can create a constant union value with field `a` and read from field `b`
* can dereference references into constants
* can create references inside constants (`const X: &u32 = &22`)
* Tuple struct constructors can be used in constants
* regression in const eval errors spans (some of these need improvements in mir debug info)
* can cast floats to ints and vice versa (in constants, and even nan/inf constants)
* Mir dump prints false/true instead of 0u8/1u8
* `1i8 >> [8][0]` does not lint about exceeding bitshifts anymore.
    * Needs const propagation across projections
* `foo[I]` produces a const eval lint if `foo: [T; N]` and `N < I`
    * Essentially all builtin panics produce lints if they can be statically proven to trigger at runtime. This is on a best effort basis, so there might be some complex cases that don't trigger. (The runtime panic stays there, irrelevant of whether the lint is produced or not)
* can use `union`s to implement `transmute` for `Copy` types in constants without a feature gate. With all the greatness and nasal demons that come with this.
* can convert integers to `&'static T` in constants (useful for embedded)

fixes #34997 (stack overflow with many constants)
fixes #25574 (deref byte strings in patterns)
fixes #27918 (broken mir ICE)
fixes #46114 (ICE on struct constructors in patterns)
fixes #37448 (`SomeStruct { foo } as SomeStruct`)
fixes #43754 (`return` in const fn)
fixes #41898 (tuple struct constructors)
fixes #31364 (infinite recursion with const fn, fixed by miri's recursion limit)
closes #29947 (const indexing stabilization)
fixes #45044 (pattern matching repeat expressions)
fixes #47971 (ICE on const fn + references)
fixes #48081 (ICE on cyclic assoc const error)
fixes #48746 (nonhelpful error message with unions)

r? @eddyb

even though 1k loc are added in tests, this PR reduces the loc in this repository by 700

src/doc/rustc-ux-guidelines.md

@@ -64,7 +64,6 @@ for details on how to format and write long error codes.
   [librustc](https://github.com/rust-lang/rust/blob/master/src/librustc/diagnostics.rs),
   [libsyntax](https://github.com/rust-lang/rust/blob/master/src/libsyntax/diagnostics.rs),
   [librustc_borrowck](https://github.com/rust-lang/rust/blob/master/src/librustc_borrowck/diagnostics.rs),
-  [librustc_const_eval](https://github.com/rust-lang/rust/blob/master/src/librustc_const_eval/diagnostics.rs),
   [librustc_metadata](https://github.com/rust-lang/rust/blob/master/src/librustc_metadata/diagnostics.rs),
   [librustc_mir](https://github.com/rust-lang/rust/blob/master/src/librustc_mir/diagnostics.rs),
   [librustc_passes](https://github.com/rust-lang/rust/blob/master/src/librustc_passes/diagnostics.rs),

src/libcore/cmp.rs

@@ -427,6 +427,7 @@ impl<T: Ord> Ord for Reverse<T> {
 ///     }
 /// }
 /// ```
+#[cfg_attr(not(stage0), lang = "ord")]
 #[stable(feature = "rust1", since = "1.0.0")]
 pub trait Ord: Eq + PartialOrd<Self> {
     /// This method returns an `Ordering` between `self` and `other`.
@@ -596,7 +597,8 @@ impl PartialOrd for Ordering {
 /// assert_eq!(x < y, true);
 /// assert_eq!(x.lt(&y), true);
 /// ```
-#[lang = "ord"]
+#[cfg_attr(stage0, lang = "ord")]
+#[cfg_attr(not(stage0), lang = "partial_ord")]
 #[stable(feature = "rust1", since = "1.0.0")]
 #[rustc_on_unimplemented = "can't compare `{Self}` with `{Rhs}`"]
 pub trait PartialOrd<Rhs: ?Sized = Self>: PartialEq<Rhs> {

src/librustc/dep_graph/dep_node.rs

@@ -60,15 +60,15 @@
 //! user of the `DepNode` API of having to know how to compute the expected
 //! fingerprint for a given set of node parameters.
 
+use mir::interpret::{GlobalId};
 use hir::def_id::{CrateNum, DefId, DefIndex, CRATE_DEF_INDEX};
 use hir::map::DefPathHash;
 use hir::{HirId, ItemLocalId};
 
-use ich::Fingerprint;
+use ich::{Fingerprint, StableHashingContext};
+use rustc_data_structures::stable_hasher::{StableHasher, HashStable};
 use ty::{TyCtxt, Instance, InstanceDef, ParamEnv, ParamEnvAnd, PolyTraitRef, Ty};
 use ty::subst::Substs;
-use rustc_data_structures::stable_hasher::{StableHasher, HashStable};
-use ich::StableHashingContext;
 use std::fmt;
 use std::hash::Hash;
 use syntax_pos::symbol::InternedString;
@@ -518,7 +518,7 @@ define_dep_nodes!( <'tcx>
     [] TypeckTables(DefId),
     [] UsedTraitImports(DefId),
     [] HasTypeckTables(DefId),
-    [] ConstEval { param_env: ParamEnvAnd<'tcx, (DefId, &'tcx Substs<'tcx>)> },
+    [] ConstEval { param_env: ParamEnvAnd<'tcx, GlobalId<'tcx>> },
     [] CheckMatch(DefId),
     [] SymbolName(DefId),
     [] InstanceSymbolName { instance: Instance<'tcx> },
@@ -663,7 +663,7 @@ trait DepNodeParams<'a, 'gcx: 'tcx + 'a, 'tcx: 'a> : fmt::Debug {
 }
 
 impl<'a, 'gcx: 'tcx + 'a, 'tcx: 'a, T> DepNodeParams<'a, 'gcx, 'tcx> for T
-    where T: HashStable<StableHashingContext<'gcx>> + fmt::Debug
+    where T: HashStable<StableHashingContext<'a>> + fmt::Debug
 {
     default const CAN_RECONSTRUCT_QUERY_KEY: bool = false;
 

src/librustc/diagnostics.rs

@@ -14,19 +14,6 @@
 // Each message should start and end with a new line, and be wrapped to 80 characters.
 // In vim you can `:set tw=80` and use `gq` to wrap paragraphs. Use `:set tw=0` to disable.
 register_long_diagnostics! {
-E0020: r##"
-This error indicates that an attempt was made to divide by zero (or take the
-remainder of a zero divisor) in a static or constant expression. Erroneous
-code example:
-
-```compile_fail
-#[deny(const_err)]
-
-const X: i32 = 42 / 0;
-// error: attempt to divide by zero in a constant expression
-```
-"##,
-
 E0038: r##"
 Trait objects like `Box<Trait>` can only be constructed when certain
 requirements are satisfied by the trait in question.

src/librustc/hir/def_id.rs

@@ -220,7 +220,6 @@ impl serialize::UseSpecializedDecodable for DefId {}
 pub struct LocalDefId(DefIndex);
 
 impl LocalDefId {
-
     #[inline]
     pub fn from_def_id(def_id: DefId) -> LocalDefId {
         assert!(def_id.is_local());

src/librustc/hir/map/collector.rs

@@ -529,7 +529,7 @@ struct HirItemLike<T> {
     hash_bodies: bool,
 }
 
-impl<'hir, T> HashStable<StableHashingContext<'hir>> for HirItemLike<T>
+impl<'a, 'hir, T> HashStable<StableHashingContext<'hir>> for HirItemLike<T>
     where T: HashStable<StableHashingContext<'hir>>
 {
     fn hash_stable<W: StableHasherResult>(&self,

src/librustc/ich/hcx.rs

@@ -46,19 +46,19 @@ pub fn compute_ignored_attr_names() -> FxHashSet<Symbol> {
 /// a reference to the TyCtxt) and it holds a few caches for speeding up various
 /// things (e.g. each DefId/DefPath is only hashed once).
 #[derive(Clone)]
-pub struct StableHashingContext<'gcx> {
-    sess: &'gcx Session,
-    definitions: &'gcx Definitions,
-    cstore: &'gcx dyn CrateStore,
-    body_resolver: BodyResolver<'gcx>,
+pub struct StableHashingContext<'a> {
+    sess: &'a Session,
+    definitions: &'a Definitions,
+    cstore: &'a dyn CrateStore,
+    body_resolver: BodyResolver<'a>,
     hash_spans: bool,
     hash_bodies: bool,
     node_id_hashing_mode: NodeIdHashingMode,
 
     // Very often, we are hashing something that does not need the
     // CachingCodemapView, so we initialize it lazily.
-    raw_codemap: &'gcx CodeMap,
-    caching_codemap: Option<CachingCodemapView<'gcx>>,
+    raw_codemap: &'a CodeMap,
+    caching_codemap: Option<CachingCodemapView<'a>>,
 }
 
 #[derive(PartialEq, Eq, Clone, Copy)]
@@ -81,14 +81,14 @@ impl<'gcx> BodyResolver<'gcx> {
     }
 }
 
-impl<'gcx> StableHashingContext<'gcx> {
+impl<'a> StableHashingContext<'a> {
     // The `krate` here is only used for mapping BodyIds to Bodies.
     // Don't use it for anything else or you'll run the risk of
     // leaking data out of the tracking system.
-    pub fn new(sess: &'gcx Session,
-               krate: &'gcx hir::Crate,
-               definitions: &'gcx Definitions,
-               cstore: &'gcx dyn CrateStore)
+    pub fn new(sess: &'a Session,
+               krate: &'a hir::Crate,
+               definitions: &'a Definitions,
+               cstore: &'a dyn CrateStore)
                -> Self {
         let hash_spans_initial = !sess.opts.debugging_opts.incremental_ignore_spans;
 
@@ -106,7 +106,7 @@ impl<'gcx> StableHashingContext<'gcx> {
     }
 
     #[inline]
-    pub fn sess(&self) -> &'gcx Session {
+    pub fn sess(&self) -> &'a Session {
         self.sess
     }
 
@@ -165,7 +165,7 @@ impl<'gcx> StableHashingContext<'gcx> {
     }
 
     #[inline]
-    pub fn codemap(&mut self) -> &mut CachingCodemapView<'gcx> {
+    pub fn codemap(&mut self) -> &mut CachingCodemapView<'a> {
         match self.caching_codemap {
             Some(ref mut cm) => {
                 cm
@@ -193,38 +193,38 @@ impl<'gcx> StableHashingContext<'gcx> {
 }
 
 impl<'a, 'gcx, 'lcx> StableHashingContextProvider for TyCtxt<'a, 'gcx, 'lcx> {
-    type ContextType = StableHashingContext<'gcx>;
+    type ContextType = StableHashingContext<'a>;
     fn create_stable_hashing_context(&self) -> Self::ContextType {
         (*self).create_stable_hashing_context()
     }
 }
 
 
-impl<'gcx> StableHashingContextProvider for StableHashingContext<'gcx> {
-    type ContextType = StableHashingContext<'gcx>;
+impl<'a> StableHashingContextProvider for StableHashingContext<'a> {
+    type ContextType = StableHashingContext<'a>;
     fn create_stable_hashing_context(&self) -> Self::ContextType {
         self.clone()
     }
 }
 
-impl<'gcx> ::dep_graph::DepGraphSafe for StableHashingContext<'gcx> {
+impl<'a> ::dep_graph::DepGraphSafe for StableHashingContext<'a> {
 }
 
 
-impl<'gcx> HashStable<StableHashingContext<'gcx>> for hir::BodyId {
+impl<'a> HashStable<StableHashingContext<'a>> for hir::BodyId {
     fn hash_stable<W: StableHasherResult>(&self,
-                                          hcx: &mut StableHashingContext<'gcx>,
+                                          hcx: &mut StableHashingContext<'a>,
                                           hasher: &mut StableHasher<W>) {
         if hcx.hash_bodies() {
             hcx.body_resolver.body(*self).hash_stable(hcx, hasher);
         }
     }
 }
 
-impl<'gcx> HashStable<StableHashingContext<'gcx>> for hir::HirId {
+impl<'a> HashStable<StableHashingContext<'a>> for hir::HirId {
     #[inline]
     fn hash_stable<W: StableHasherResult>(&self,
-                                          hcx: &mut StableHashingContext<'gcx>,
+                                          hcx: &mut StableHashingContext<'a>,
                                           hasher: &mut StableHasher<W>) {
         match hcx.node_id_hashing_mode {
             NodeIdHashingMode::Ignore => {
@@ -243,21 +243,21 @@ impl<'gcx> HashStable<StableHashingContext<'gcx>> for hir::HirId {
     }
 }
 
-impl<'gcx> ToStableHashKey<StableHashingContext<'gcx>> for hir::HirId {
+impl<'a> ToStableHashKey<StableHashingContext<'a>> for hir::HirId {
     type KeyType = (DefPathHash, hir::ItemLocalId);
 
     #[inline]
     fn to_stable_hash_key(&self,
-                          hcx: &StableHashingContext<'gcx>)
+                          hcx: &StableHashingContext<'a>)
                           -> (DefPathHash, hir::ItemLocalId) {
         let def_path_hash = hcx.local_def_path_hash(self.owner);
         (def_path_hash, self.local_id)
     }
 }
 
-impl<'gcx> HashStable<StableHashingContext<'gcx>> for ast::NodeId {
+impl<'a> HashStable<StableHashingContext<'a>> for ast::NodeId {
     fn hash_stable<W: StableHasherResult>(&self,
-                                          hcx: &mut StableHashingContext<'gcx>,
+                                          hcx: &mut StableHashingContext<'a>,
                                           hasher: &mut StableHasher<W>) {
         match hcx.node_id_hashing_mode {
             NodeIdHashingMode::Ignore => {
@@ -270,18 +270,18 @@ impl<'gcx> HashStable<StableHashingContext<'gcx>> for ast::NodeId {
     }
 }
 
-impl<'gcx> ToStableHashKey<StableHashingContext<'gcx>> for ast::NodeId {
+impl<'a> ToStableHashKey<StableHashingContext<'a>> for ast::NodeId {
     type KeyType = (DefPathHash, hir::ItemLocalId);
 
     #[inline]
     fn to_stable_hash_key(&self,
-                          hcx: &StableHashingContext<'gcx>)
+                          hcx: &StableHashingContext<'a>)
                           -> (DefPathHash, hir::ItemLocalId) {
         hcx.definitions.node_to_hir_id(*self).to_stable_hash_key(hcx)
     }
 }
 
-impl<'gcx> HashStable<StableHashingContext<'gcx>> for Span {
+impl<'a> HashStable<StableHashingContext<'a>> for Span {
 
     // Hash a span in a stable way. We can't directly hash the span's BytePos
     // fields (that would be similar to hashing pointers, since those are just
@@ -293,7 +293,7 @@ impl<'gcx> HashStable<StableHashingContext<'gcx>> for Span {
     // Also, hashing filenames is expensive so we avoid doing it twice when the
     // span starts and ends in the same file, which is almost always the case.
     fn hash_stable<W: StableHasherResult>(&self,
-                                          hcx: &mut StableHashingContext<'gcx>,
+                                          hcx: &mut StableHashingContext<'a>,
                                           hasher: &mut StableHasher<W>) {
         const TAG_VALID_SPAN: u8 = 0;
         const TAG_INVALID_SPAN: u8 = 1;
@@ -373,8 +373,8 @@ impl<'gcx> HashStable<StableHashingContext<'gcx>> for Span {
     }
 }
 
-pub fn hash_stable_trait_impls<'gcx, W, R>(
-    hcx: &mut StableHashingContext<'gcx>,
+pub fn hash_stable_trait_impls<'a, 'gcx, W, R>(
+    hcx: &mut StableHashingContext<'a>,
     hasher: &mut StableHasher<W>,
     blanket_impls: &Vec<DefId>,
     non_blanket_impls: &HashMap<fast_reject::SimplifiedType, Vec<DefId>, R>)