Rollup merge of rust-lang#88709 - BoxyUwU:thir-abstract-const, r=lcnr

generic_const_exprs: use thir for abstract consts instead of mir

Changes `AbstractConst` building to use `thir` instead of `mir` so that there's less chance of consts unifying when they shouldn't because lowering to mir dropped information (see `abstract-consts-as-cast-5.rs` test)

r? `@lcnr`

Author: Manishearth

compiler/rustc_metadata/src/rmeta/decoder.rs

@@ -26,6 +26,7 @@ use rustc_middle::middle::cstore::{ForeignModule, LinkagePreference, NativeLib};
 use rustc_middle::middle::exported_symbols::{ExportedSymbol, SymbolExportLevel};
 use rustc_middle::mir::interpret::{AllocDecodingSession, AllocDecodingState};
 use rustc_middle::mir::{self, Body, Promoted};
+use rustc_middle::thir;
 use rustc_middle::ty::codec::TyDecoder;
 use rustc_middle::ty::{self, Ty, TyCtxt, Visibility};
 use rustc_serialize::{opaque, Decodable, Decoder};
@@ -541,7 +542,7 @@ impl<'a, 'tcx> Decodable<DecodeContext<'a, 'tcx>> for Span {
     }
 }
 
-impl<'a, 'tcx> Decodable<DecodeContext<'a, 'tcx>> for &'tcx [mir::abstract_const::Node<'tcx>] {
+impl<'a, 'tcx> Decodable<DecodeContext<'a, 'tcx>> for &'tcx [thir::abstract_const::Node<'tcx>] {
     fn decode(d: &mut DecodeContext<'a, 'tcx>) -> Result<Self, String> {
         ty::codec::RefDecodable::decode(d)
     }
@@ -1196,14 +1197,14 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
             .decode((self, tcx))
     }
 
-    fn get_mir_abstract_const(
+    fn get_thir_abstract_const(
         &self,
         tcx: TyCtxt<'tcx>,
         id: DefIndex,
-    ) -> Result<Option<&'tcx [mir::abstract_const::Node<'tcx>]>, ErrorReported> {
+    ) -> Result<Option<&'tcx [thir::abstract_const::Node<'tcx>]>, ErrorReported> {
         self.root
             .tables
-            .mir_abstract_consts
+            .thir_abstract_consts
             .get(self, id)
             .map_or(Ok(None), |v| Ok(Some(v.decode((self, tcx)))))
     }

compiler/rustc_metadata/src/rmeta/decoder/cstore_impl.rs

@@ -116,7 +116,7 @@ provide! { <'tcx> tcx, def_id, other, cdata,
     optimized_mir => { tcx.arena.alloc(cdata.get_optimized_mir(tcx, def_id.index)) }
     mir_for_ctfe => { tcx.arena.alloc(cdata.get_mir_for_ctfe(tcx, def_id.index)) }
     promoted_mir => { tcx.arena.alloc(cdata.get_promoted_mir(tcx, def_id.index)) }
-    mir_abstract_const => { cdata.get_mir_abstract_const(tcx, def_id.index) }
+    thir_abstract_const => { cdata.get_thir_abstract_const(tcx, def_id.index) }
     unused_generic_params => { cdata.get_unused_generic_params(def_id.index) }
     const_param_default => { tcx.mk_const(cdata.get_const_param_default(tcx, def_id.index)) }
     mir_const_qualif => { cdata.mir_const_qualif(def_id.index) }

compiler/rustc_metadata/src/rmeta/encoder.rs

@@ -23,6 +23,7 @@ use rustc_middle::middle::exported_symbols::{
     metadata_symbol_name, ExportedSymbol, SymbolExportLevel,
 };
 use rustc_middle::mir::interpret;
+use rustc_middle::thir;
 use rustc_middle::traits::specialization_graph;
 use rustc_middle::ty::codec::TyEncoder;
 use rustc_middle::ty::{self, SymbolName, Ty, TyCtxt};
@@ -344,7 +345,7 @@ impl<'a, 'tcx> TyEncoder<'tcx> for EncodeContext<'a, 'tcx> {
     }
 }
 
-impl<'a, 'tcx> Encodable<EncodeContext<'a, 'tcx>> for &'tcx [mir::abstract_const::Node<'tcx>] {
+impl<'a, 'tcx> Encodable<EncodeContext<'a, 'tcx>> for &'tcx [thir::abstract_const::Node<'tcx>] {
     fn encode(&self, s: &mut EncodeContext<'a, 'tcx>) -> opaque::EncodeResult {
         (**self).encode(s)
     }
@@ -1297,9 +1298,10 @@ impl EncodeContext<'a, 'tcx> {
             if encode_const {
                 record!(self.tables.mir_for_ctfe[def_id.to_def_id()] <- self.tcx.mir_for_ctfe(def_id));
 
-                let abstract_const = self.tcx.mir_abstract_const(def_id);
+                // FIXME(generic_const_exprs): this feels wrong to have in `encode_mir`
+                let abstract_const = self.tcx.thir_abstract_const(def_id);
                 if let Ok(Some(abstract_const)) = abstract_const {
-                    record!(self.tables.mir_abstract_consts[def_id.to_def_id()] <- abstract_const);
+                    record!(self.tables.thir_abstract_consts[def_id.to_def_id()] <- abstract_const);
                 }
             }
             record!(self.tables.promoted_mir[def_id.to_def_id()] <- self.tcx.promoted_mir(def_id));

compiler/rustc_metadata/src/rmeta/mod.rs

@@ -15,6 +15,7 @@ use rustc_middle::hir::exports::Export;
 use rustc_middle::middle::cstore::{CrateDepKind, ForeignModule, LinkagePreference, NativeLib};
 use rustc_middle::middle::exported_symbols::{ExportedSymbol, SymbolExportLevel};
 use rustc_middle::mir;
+use rustc_middle::thir;
 use rustc_middle::ty::{self, ReprOptions, Ty};
 use rustc_serialize::opaque::Encoder;
 use rustc_session::config::SymbolManglingVersion;
@@ -305,7 +306,7 @@ define_tables! {
     mir: Table<DefIndex, Lazy!(mir::Body<'tcx>)>,
     mir_for_ctfe: Table<DefIndex, Lazy!(mir::Body<'tcx>)>,
     promoted_mir: Table<DefIndex, Lazy!(IndexVec<mir::Promoted, mir::Body<'tcx>>)>,
-    mir_abstract_consts: Table<DefIndex, Lazy!(&'tcx [mir::abstract_const::Node<'tcx>])>,
+    thir_abstract_consts: Table<DefIndex, Lazy!(&'tcx [thir::abstract_const::Node<'tcx>])>,
     const_defaults: Table<DefIndex, Lazy<rustc_middle::ty::Const<'tcx>>>,
     unused_generic_params: Table<DefIndex, Lazy<FiniteBitSet<u32>>>,
     // `def_keys` and `def_path_hashes` represent a lazy version of a

compiler/rustc_middle/src/mir/abstract_const.rs

@@ -40,7 +40,6 @@ use self::graph_cyclic_cache::GraphIsCyclicCache;
 use self::predecessors::{PredecessorCache, Predecessors};
 pub use self::query::*;
 
-pub mod abstract_const;
 pub mod coverage;
 mod generic_graph;
 pub mod generic_graphviz;

compiler/rustc_middle/src/mir/mod.rs

@@ -1,6 +1,6 @@
 //! Values computed by queries that use MIR.
 
-use crate::mir::{abstract_const, Body, Promoted};
+use crate::mir::{Body, Promoted};
 use crate::ty::{self, Ty, TyCtxt};
 use rustc_data_structures::sync::Lrc;
 use rustc_data_structures::vec_map::VecMap;
@@ -431,16 +431,4 @@ impl<'tcx> TyCtxt<'tcx> {
             self.mir_for_ctfe(def.did)
         }
     }
-
-    #[inline]
-    pub fn mir_abstract_const_opt_const_arg(
-        self,
-        def: ty::WithOptConstParam<DefId>,
-    ) -> Result<Option<&'tcx [abstract_const::Node<'tcx>]>, ErrorReported> {
-        if let Some((did, param_did)) = def.as_const_arg() {
-            self.mir_abstract_const_of_const_arg((did, param_did))
-        } else {
-            self.mir_abstract_const(def.did)
-        }
-    }
 }

compiler/rustc_middle/src/mir/query.rs

@@ -303,17 +303,17 @@ rustc_queries! {
     }
 
     /// Try to build an abstract representation of the given constant.
-    query mir_abstract_const(
+    query thir_abstract_const(
         key: DefId
-    ) -> Result<Option<&'tcx [mir::abstract_const::Node<'tcx>]>, ErrorReported> {
+    ) -> Result<Option<&'tcx [thir::abstract_const::Node<'tcx>]>, ErrorReported> {
         desc {
             |tcx| "building an abstract representation for {}", tcx.def_path_str(key),
         }
     }
     /// Try to build an abstract representation of the given constant.
-    query mir_abstract_const_of_const_arg(
+    query thir_abstract_const_of_const_arg(
         key: (LocalDefId, DefId)
-    ) -> Result<Option<&'tcx [mir::abstract_const::Node<'tcx>]>, ErrorReported> {
+    ) -> Result<Option<&'tcx [thir::abstract_const::Node<'tcx>]>, ErrorReported> {
         desc {
             |tcx|
             "building an abstract representation for the const argument {}",

compiler/rustc_middle/src/query/mod.rs

@@ -33,6 +33,9 @@ use rustc_target::asm::InlineAsmRegOrRegClass;
 use std::fmt;
 use std::ops::Index;
 
+pub mod abstract_const;
+pub mod visit;
+
 newtype_index! {
     /// An index to an [`Arm`] stored in [`Thir::arms`]
     #[derive(HashStable)]

compiler/rustc_middle/src/thir.rs

@@ -0,0 +1,61 @@
+//! A subset of a mir body used for const evaluatability checking.
+use crate::mir;
+use crate::ty::{self, Ty, TyCtxt};
+use rustc_errors::ErrorReported;
+
+rustc_index::newtype_index! {
+    /// An index into an `AbstractConst`.
+    pub struct NodeId {
+        derive [HashStable]
+        DEBUG_FORMAT = "n{}",
+    }
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq, HashStable, TyEncodable, TyDecodable)]
+pub enum CastKind {
+    /// thir::ExprKind::As
+    As,
+    /// thir::ExprKind::Use
+    Use,
+}
+
+/// A node of an `AbstractConst`.
+#[derive(Debug, Clone, Copy, PartialEq, Eq, HashStable, TyEncodable, TyDecodable)]
+pub enum Node<'tcx> {
+    Leaf(&'tcx ty::Const<'tcx>),
+    Binop(mir::BinOp, NodeId, NodeId),
+    UnaryOp(mir::UnOp, NodeId),
+    FunctionCall(NodeId, &'tcx [NodeId]),
+    Cast(CastKind, NodeId, Ty<'tcx>),
+}
+
+#[derive(Debug, Copy, Clone, PartialEq, Eq, HashStable, TyEncodable, TyDecodable)]
+pub enum NotConstEvaluatable {
+    Error(ErrorReported),
+    MentionsInfer,
+    MentionsParam,
+}
+
+impl From<ErrorReported> for NotConstEvaluatable {
+    fn from(e: ErrorReported) -> NotConstEvaluatable {
+        NotConstEvaluatable::Error(e)
+    }
+}
+
+TrivialTypeFoldableAndLiftImpls! {
+    NotConstEvaluatable,
+}
+
+impl<'tcx> TyCtxt<'tcx> {
+    #[inline]
+    pub fn thir_abstract_const_opt_const_arg(
+        self,
+        def: ty::WithOptConstParam<rustc_hir::def_id::DefId>,
+    ) -> Result<Option<&'tcx [Node<'tcx>]>, ErrorReported> {
+        if let Some((did, param_did)) = def.as_const_arg() {
+            self.thir_abstract_const_of_const_arg((did, param_did))
+        } else {
+            self.thir_abstract_const(def.did)
+        }
+    }
+}