Merge branch 'master' into feature/print-msg-from-elf-entrypoint

Author: Pagten

src/libcore/intrinsics.rs

@@ -939,6 +939,7 @@ extern "rust-intrinsic" {
     /// }
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
+    #[rustc_const_unstable(feature = "const_transmute")]
     pub fn transmute<T, U>(e: T) -> U;
 
     /// Returns `true` if the actual type given as `T` requires drop

src/librustc/ty/constness.rs

@@ -2,7 +2,8 @@ use crate::ty::query::Providers;
 use crate::hir::def_id::DefId;
 use crate::hir;
 use crate::ty::TyCtxt;
-use syntax_pos::symbol::Symbol;
+use syntax_pos::symbol::{sym, Symbol};
+use rustc_target::spec::abi::Abi;
 use crate::hir::map::blocks::FnLikeNode;
 use syntax::attr;
 
@@ -35,12 +36,51 @@ impl<'tcx> TyCtxt<'tcx> {
         }
     }
 
+    /// Returns `true` if the `def_id` refers to an intrisic which we've whitelisted
+    /// for being called from stable `const fn`s (`min_const_fn`).
+    ///
+    /// Adding more intrinsics requires sign-off from @rust-lang/lang.
+    ///
+    /// This list differs from the list in `is_const_intrinsic` in the sense that any item on this
+    /// list must be on the `is_const_intrinsic` list, too, because if an intrinsic is callable from
+    /// stable, it must be callable at all.
+    fn is_intrinsic_min_const_fn(self, def_id: DefId) -> bool {
+        match self.item_name(def_id) {
+            | sym::size_of
+            | sym::min_align_of
+            | sym::needs_drop
+            // Arithmetic:
+            | sym::add_with_overflow // ~> .overflowing_add
+            | sym::sub_with_overflow // ~> .overflowing_sub
+            | sym::mul_with_overflow // ~> .overflowing_mul
+            | sym::wrapping_add // ~> .wrapping_add
+            | sym::wrapping_sub // ~> .wrapping_sub
+            | sym::wrapping_mul // ~> .wrapping_mul
+            | sym::saturating_add // ~> .saturating_add
+            | sym::saturating_sub // ~> .saturating_sub
+            | sym::unchecked_shl // ~> .wrapping_shl
+            | sym::unchecked_shr // ~> .wrapping_shr
+            | sym::rotate_left // ~> .rotate_left
+            | sym::rotate_right // ~> .rotate_right
+            | sym::ctpop // ~> .count_ones
+            | sym::ctlz // ~> .leading_zeros
+            | sym::cttz // ~> .trailing_zeros
+            | sym::bswap // ~> .swap_bytes
+            | sym::bitreverse // ~> .reverse_bits
+            => true,
+            _ => false,
+        }
+    }
+
     /// Returns `true` if this function must conform to `min_const_fn`
     pub fn is_min_const_fn(self, def_id: DefId) -> bool {
         // Bail out if the signature doesn't contain `const`
         if !self.is_const_fn_raw(def_id) {
             return false;
         }
+        if let Abi::RustIntrinsic = self.fn_sig(def_id).abi() {
+            return self.is_intrinsic_min_const_fn(def_id);
+        }
 
         if self.features().staged_api {
             // in order for a libstd function to be considered min_const_fn
@@ -63,13 +103,82 @@ impl<'tcx> TyCtxt<'tcx> {
 
 
 pub fn provide(providers: &mut Providers<'_>) {
-    /// only checks whether the function has a `const` modifier
+    /// Const evaluability whitelist is here to check evaluability at the
+    /// top level beforehand.
+    fn is_const_intrinsic(tcx: TyCtxt<'_>, def_id: DefId) -> Option<bool> {
+        match tcx.fn_sig(def_id).abi() {
+            Abi::RustIntrinsic |
+            Abi::PlatformIntrinsic => {
+                // FIXME: deduplicate these two lists as much as possible
+                match tcx.item_name(def_id) {
+                    // Keep this list in the same order as the match patterns in
+                    // `librustc_mir/interpret/intrinsics.rs`
+
+                    // This whitelist is a list of intrinsics that have a miri-engine implementation
+                    // and can thus be called when enabling enough feature gates. The similar
+                    // whitelist in `is_intrinsic_min_const_fn` (in this file), exists for allowing
+                    // the intrinsics to be called by stable const fns.
+                    | sym::caller_location
+
+                    | sym::min_align_of
+                    | sym::pref_align_of
+                    | sym::needs_drop
+                    | sym::size_of
+                    | sym::type_id
+                    | sym::type_name
+
+                    | sym::ctpop
+                    | sym::cttz
+                    | sym::cttz_nonzero
+                    | sym::ctlz
+                    | sym::ctlz_nonzero
+                    | sym::bswap
+                    | sym::bitreverse
+
+                    | sym::wrapping_add
+                    | sym::wrapping_sub
+                    | sym::wrapping_mul
+                    | sym::add_with_overflow
+                    | sym::sub_with_overflow
+                    | sym::mul_with_overflow
+
+                    | sym::saturating_add
+                    | sym::saturating_sub
+
+                    | sym::unchecked_shl
+                    | sym::unchecked_shr
+
+                    | sym::rotate_left
+                    | sym::rotate_right
+
+                    | sym::ptr_offset_from
+
+                    | sym::transmute
+
+                    | sym::simd_insert
+
+                    | sym::simd_extract
+
+                    => Some(true),
+
+                    _ => Some(false)
+                }
+            }
+            _ => None
+        }
+    }
+
+    /// Checks whether the function has a `const` modifier or, in case it is an intrinsic, whether
+    /// said intrinsic is on the whitelist for being const callable.
     fn is_const_fn_raw(tcx: TyCtxt<'_>, def_id: DefId) -> bool {
         let hir_id = tcx.hir().as_local_hir_id(def_id)
                               .expect("Non-local call to local provider is_const_fn");
 
         let node = tcx.hir().get(hir_id);
-        if let Some(fn_like) = FnLikeNode::from_node(node) {
+
+        if let Some(whitelisted) = is_const_intrinsic(tcx, def_id) {
+            whitelisted
+        } else if let Some(fn_like) = FnLikeNode::from_node(node) {
             fn_like.constness() == hir::Constness::Const
         } else if let hir::Node::Ctor(_) = node {
             true

src/librustc_data_structures/obligation_forest/mod.rs

@@ -395,7 +395,16 @@ impl<O: ForestObligation> ObligationForest<O> {
         let mut errors = vec![];
         let mut stalled = true;
 
-        for index in 0..self.nodes.len() {
+        // Note that the loop body can append new nodes, and those new nodes
+        // will then be processed by subsequent iterations of the loop.
+        //
+        // We can't use an iterator for the loop because `self.nodes` is
+        // appended to and the borrow checker would complain. We also can't use
+        // `for index in 0..self.nodes.len() { ... }` because the range would
+        // be computed with the initial length, and we would miss the appended
+        // nodes. Therefore we use a `while` loop.
+        let mut index = 0;
+        while index < self.nodes.len() {
             let node = &mut self.nodes[index];
 
             debug!("process_obligations: node {} == {:?}", index, node);
@@ -406,6 +415,7 @@ impl<O: ForestObligation> ObligationForest<O> {
             // out of sync with `nodes`. It's not very common, but it does
             // happen, and code in `compress` has to allow for it.
             if node.state.get() != NodeState::Pending {
+                index += 1;
                 continue;
             }
             let result = processor.process_obligation(&mut node.obligation);
@@ -441,6 +451,7 @@ impl<O: ForestObligation> ObligationForest<O> {
                     });
                 }
             }
+            index += 1;
         }
 
         if stalled {

src/librustc_data_structures/obligation_forest/tests.rs

@@ -70,6 +70,7 @@ fn push_pop() {
                 "A" => ProcessResult::Changed(vec!["A.1", "A.2", "A.3"]),
                 "B" => ProcessResult::Error("B is for broken"),
                 "C" => ProcessResult::Changed(vec![]),
+                "A.1" | "A.2" | "A.3" => ProcessResult::Unchanged,
                 _ => unreachable!(),
             }
         }, |_| {}), DoCompleted::Yes);
@@ -94,6 +95,7 @@ fn push_pop() {
                 "A.2" => ProcessResult::Unchanged,
                 "A.3" => ProcessResult::Changed(vec!["A.3.i"]),
                 "D" => ProcessResult::Changed(vec!["D.1", "D.2"]),
+                "A.3.i" | "D.1" | "D.2" => ProcessResult::Unchanged,
                 _ => unreachable!(),
             }
         }, |_| {}), DoCompleted::Yes);
@@ -113,6 +115,7 @@ fn push_pop() {
                 "A.3.i" => ProcessResult::Changed(vec![]),
                 "D.1" => ProcessResult::Changed(vec!["D.1.i"]),
                 "D.2" => ProcessResult::Changed(vec!["D.2.i"]),
+                "D.1.i" | "D.2.i" => ProcessResult::Unchanged,
                 _ => unreachable!(),
             }
         }, |_| {}), DoCompleted::Yes);
@@ -161,35 +164,38 @@ fn success_in_grandchildren() {
         forest.process_obligations(&mut C(|obligation| {
             match *obligation {
                 "A" => ProcessResult::Changed(vec!["A.1", "A.2", "A.3"]),
+                "A.1" => ProcessResult::Changed(vec![]),
+                "A.2" => ProcessResult::Changed(vec!["A.2.i", "A.2.ii"]),
+                "A.3" => ProcessResult::Changed(vec![]),
+                "A.2.i" | "A.2.ii" => ProcessResult::Unchanged,
                 _ => unreachable!(),
             }
         }, |_| {}), DoCompleted::Yes);
-    assert!(ok.unwrap().is_empty());
+    let mut ok = ok.unwrap();
+    ok.sort();
+    assert_eq!(ok, vec!["A.1", "A.3"]);
     assert!(err.is_empty());
 
     let Outcome { completed: ok, errors: err, .. } =
         forest.process_obligations(&mut C(|obligation| {
             match *obligation {
-                "A.1" => ProcessResult::Changed(vec![]),
-                "A.2" => ProcessResult::Changed(vec!["A.2.i", "A.2.ii"]),
-                "A.3" => ProcessResult::Changed(vec![]),
+                "A.2.i" => ProcessResult::Unchanged,
+                "A.2.ii" => ProcessResult::Changed(vec![]),
                 _ => unreachable!(),
             }
         }, |_| {}), DoCompleted::Yes);
-    let mut ok = ok.unwrap();
-    ok.sort();
-    assert_eq!(ok, vec!["A.1", "A.3"]);
+    assert_eq!(ok.unwrap(), vec!["A.2.ii"]);
     assert!(err.is_empty());
 
     let Outcome { completed: ok, errors: err, .. } =
         forest.process_obligations(&mut C(|obligation| {
             match *obligation {
                 "A.2.i" => ProcessResult::Changed(vec!["A.2.i.a"]),
-                "A.2.ii" => ProcessResult::Changed(vec![]),
+                "A.2.i.a" => ProcessResult::Unchanged,
                 _ => unreachable!(),
             }
         }, |_| {}), DoCompleted::Yes);
-    assert_eq!(ok.unwrap(), vec!["A.2.ii"]);
+    assert!(ok.unwrap().is_empty());
     assert!(err.is_empty());
 
     let Outcome { completed: ok, errors: err, .. } =
@@ -222,6 +228,7 @@ fn to_errors_no_throw() {
         forest.process_obligations(&mut C(|obligation| {
             match *obligation {
                 "A" => ProcessResult::Changed(vec!["A.1", "A.2", "A.3"]),
+                "A.1" | "A.2" | "A.3" => ProcessResult::Unchanged,
                 _ => unreachable!(),
             }
         }, |_|{}), DoCompleted::Yes);
@@ -243,6 +250,7 @@ fn diamond() {
         forest.process_obligations(&mut C(|obligation| {
             match *obligation {
                 "A" => ProcessResult::Changed(vec!["A.1", "A.2"]),
+                "A.1" | "A.2" => ProcessResult::Unchanged,
                 _ => unreachable!(),
             }
         }, |_|{}), DoCompleted::Yes);
@@ -254,6 +262,7 @@ fn diamond() {
             match *obligation {
                 "A.1" => ProcessResult::Changed(vec!["D"]),
                 "A.2" => ProcessResult::Changed(vec!["D"]),
+                "D" => ProcessResult::Unchanged,
                 _ => unreachable!(),
             }
         }, |_|{}), DoCompleted::Yes);
@@ -282,6 +291,7 @@ fn diamond() {
         forest.process_obligations(&mut C(|obligation| {
             match *obligation {
                 "A'" => ProcessResult::Changed(vec!["A'.1", "A'.2"]),
+                "A'.1" | "A'.2" => ProcessResult::Unchanged,
                 _ => unreachable!(),
             }
         }, |_|{}), DoCompleted::Yes);
@@ -293,6 +303,7 @@ fn diamond() {
             match *obligation {
                 "A'.1" => ProcessResult::Changed(vec!["D'", "A'"]),
                 "A'.2" => ProcessResult::Changed(vec!["D'"]),
+                "D'" | "A'" => ProcessResult::Unchanged,
                 _ => unreachable!(),
             }
         }, |_|{}), DoCompleted::Yes);
@@ -370,6 +381,7 @@ fn orphan() {
                 "B" => ProcessResult::Unchanged,
                 "C1" => ProcessResult::Changed(vec![]),
                 "C2" => ProcessResult::Changed(vec![]),
+                "D" | "E" => ProcessResult::Unchanged,
                 _ => unreachable!(),
             }
         }, |_|{}), DoCompleted::Yes);

src/librustc_feature/active.rs

@@ -408,10 +408,6 @@ declare_features! (
     /// Allows using `#[doc(keyword = "...")]`.
     (active, doc_keyword, "1.28.0", Some(51315), None),
 
-    /// Allows reinterpretation of the bits of a value of one type as another
-    /// type during const eval.
-    (active, const_transmute, "1.29.0", Some(53605), None),
-
     /// Allows using `try {...}` expressions.
     (active, try_blocks, "1.29.0", Some(31436), None),
 

src/librustc_metadata/rmeta/decoder.rs

@@ -1360,10 +1360,16 @@ impl<'a, 'tcx> CrateMetadata {
         }
     }
 
+    // This replicates some of the logic of the crate-local `is_const_fn_raw` query, because we
+    // don't serialize constness for tuple variant and tuple struct constructors.
     fn is_const_fn_raw(&self, id: DefIndex) -> bool {
         let constness = match self.kind(id) {
             EntryKind::Method(data) => data.decode(self).fn_data.constness,
             EntryKind::Fn(data) => data.decode(self).constness,
+            // Some intrinsics can be const fn. While we could recompute this (at least until we
+            // stop having hardcoded whitelists and move to stability attributes), it seems cleaner
+            // to treat all const fns equally.
+            EntryKind::ForeignFn(data) => data.decode(self).constness,
             EntryKind::Variant(..) | EntryKind::Struct(..) => hir::Constness::Const,
             _ => hir::Constness::NotConst,
         };

src/librustc_metadata/rmeta/encoder.rs

@@ -1525,7 +1525,11 @@ impl EncodeContext<'tcx> {
             hir::ForeignItemKind::Fn(_, ref names, _) => {
                 let data = FnData {
                     asyncness: hir::IsAsync::NotAsync,
-                    constness: hir::Constness::NotConst,
+                    constness: if self.tcx.is_const_fn_raw(def_id) {
+                        hir::Constness::Const
+                    } else {
+                        hir::Constness::NotConst
+                    },
                     param_names: self.encode_fn_param_names(names),
                 };
                 EntryKind::ForeignFn(self.lazy(data))

src/librustc_mir/const_eval.rs

@@ -328,20 +328,32 @@ impl<'mir, 'tcx> interpret::Machine<'mir, 'tcx> for CompileTimeInterpreter<'mir,
         false // for now, we don't enforce validity
     }
 
-    fn find_fn(
+    fn find_mir_or_eval_fn(
         ecx: &mut InterpCx<'mir, 'tcx, Self>,
         instance: ty::Instance<'tcx>,
         args: &[OpTy<'tcx>],
         ret: Option<(PlaceTy<'tcx>, mir::BasicBlock)>,
         _unwind: Option<mir::BasicBlock> // unwinding is not supported in consts
     ) -> InterpResult<'tcx, Option<&'mir mir::Body<'tcx>>> {
-        debug!("eval_fn_call: {:?}", instance);
+        debug!("find_mir_or_eval_fn: {:?}", instance);
+
         // Only check non-glue functions
         if let ty::InstanceDef::Item(def_id) = instance.def {
             // Execution might have wandered off into other crates, so we cannot do a stability-
             // sensitive check here.  But we can at least rule out functions that are not const
             // at all.
-            if !ecx.tcx.is_const_fn_raw(def_id) {
+            if ecx.tcx.is_const_fn_raw(def_id) {
+                // If this function is a `const fn` then as an optimization we can query this
+                // evaluation immediately.
+                //
+                // For the moment we only do this for functions which take no arguments
+                // (or all arguments are ZSTs) so that we don't memoize too much.
+                if args.iter().all(|a| a.layout.is_zst()) {
+                    let gid = GlobalId { instance, promoted: None };
+                    ecx.eval_const_fn_call(gid, ret)?;
+                    return Ok(None);
+                }
+            } else {
                 // Some functions we support even if they are non-const -- but avoid testing
                 // that for const fn!  We certainly do *not* want to actually call the fn
                 // though, so be sure we return here.