Change Thir to lazily create constants

compiler/rustc_middle/src/query/mod.rs

@@ -955,6 +955,7 @@ rustc_queries! {
         desc { "get a &core::panic::Location referring to a span" }
     }
 
+    // FIXME get rid of this with valtrees
     query lit_to_const(
         key: LitToConstInput<'tcx>
     ) -> Result<ty::Const<'tcx>, LitToConstError> {

compiler/rustc_middle/src/thir.rs

@@ -369,7 +369,8 @@ pub enum ExprKind<'tcx> {
     },
     /// An inline `const` block, e.g. `const {}`.
     ConstBlock {
-        value: Const<'tcx>,
+        did: DefId,
+        substs: SubstsRef<'tcx>,
     },
     /// An array literal constructed from one repeated element, e.g. `[1; 5]`.
     Repeat {
@@ -408,13 +409,25 @@ pub enum ExprKind<'tcx> {
     },
     /// A literal.
     Literal {
-        literal: Const<'tcx>,
+        lit: &'tcx hir::Lit,
+        neg: bool,
+    },
+    /// For literals that don't correspond to anything in the HIR
+    NonHirLiteral {
+        lit: ty::ScalarInt,
+        user_ty: Option<Canonical<'tcx, UserType<'tcx>>>,
+    },
+    /// Associated constants and named constants
+    NamedConst {
+        def_id: DefId,
+        substs: SubstsRef<'tcx>,
         user_ty: Option<Canonical<'tcx, UserType<'tcx>>>,
-        /// The `DefId` of the `const` item this literal
-        /// was produced from, if this is not a user-written
-        /// literal value.
-        const_id: Option<DefId>,
     },
+    ConstParam {
+        param: ty::ParamConst,
+        def_id: DefId,
+    },
+    // FIXME improve docs for `StaticRef` by distinguishing it from `NamedConst`
     /// A literal containing the address of a `static`.
     ///
     /// This is only distinguished from `Literal` so that we can register some
@@ -439,6 +452,12 @@ pub enum ExprKind<'tcx> {
     },
 }
 
+impl<'tcx> ExprKind<'tcx> {
+    pub fn zero_sized_literal(user_ty: Option<Canonical<'tcx, UserType<'tcx>>>) -> Self {
+        ExprKind::NonHirLiteral { lit: ty::ScalarInt::ZST, user_ty }
+    }
+}
+
 /// Represents the association of a field identifier and an expression.
 ///
 /// This is used in struct constructors.

compiler/rustc_middle/src/thir/visit.rs

@@ -1,7 +1,6 @@
 use super::{
     Arm, Block, Expr, ExprKind, Guard, InlineAsmOperand, Pat, PatKind, Stmt, StmtKind, Thir,
 };
-use rustc_middle::ty::Const;
 
 pub trait Visitor<'a, 'tcx: 'a>: Sized {
     fn thir(&self) -> &'a Thir<'tcx>;
@@ -25,8 +24,6 @@ pub trait Visitor<'a, 'tcx: 'a>: Sized {
     fn visit_pat(&mut self, pat: &Pat<'tcx>) {
         walk_pat(self, pat);
     }
-
-    fn visit_const(&mut self, _cnst: Const<'tcx>) {}
 }
 
 pub fn walk_expr<'a, 'tcx: 'a, V: Visitor<'a, 'tcx>>(visitor: &mut V, expr: &Expr<'tcx>) {
@@ -93,10 +90,9 @@ pub fn walk_expr<'a, 'tcx: 'a, V: Visitor<'a, 'tcx>>(visitor: &mut V, expr: &Exp
                 visitor.visit_expr(&visitor.thir()[value])
             }
         }
-        ConstBlock { value } => visitor.visit_const(value),
-        Repeat { value, count } => {
+        ConstBlock { did: _, substs: _ } => {}
+        Repeat { value, count: _ } => {
             visitor.visit_expr(&visitor.thir()[value]);
-            visitor.visit_const(count);
         }
         Array { ref fields } | Tuple { ref fields } => {
             for &field in &**fields {
@@ -122,7 +118,10 @@ pub fn walk_expr<'a, 'tcx: 'a, V: Visitor<'a, 'tcx>>(visitor: &mut V, expr: &Exp
             visitor.visit_expr(&visitor.thir()[source])
         }
         Closure { closure_id: _, substs: _, upvars: _, movability: _, fake_reads: _ } => {}
-        Literal { literal, user_ty: _, const_id: _ } => visitor.visit_const(literal),
+        Literal { lit: _, neg: _ } => {}
+        NonHirLiteral { lit: _, user_ty: _ } => {}
+        NamedConst { def_id: _, substs: _, user_ty: _ } => {}
+        ConstParam { param: _, def_id: _ } => {}
         StaticRef { alloc_id: _, ty: _, def_id: _ } => {}
         InlineAsm { ref operands, template: _, options: _, line_spans: _ } => {
             for op in &**operands {
@@ -209,11 +208,8 @@ pub fn walk_pat<'a, 'tcx: 'a, V: Visitor<'a, 'tcx>>(visitor: &mut V, pat: &Pat<'
                 visitor.visit_pat(&subpattern.pattern);
             }
         }
-        Constant { value } => visitor.visit_const(*value),
-        Range(range) => {
-            visitor.visit_const(range.lo);
-            visitor.visit_const(range.hi);
-        }
+        Constant { value: _ } => {}
+        Range(_) => {}
         Slice { prefix, slice, suffix } | Array { prefix, slice, suffix } => {
             for subpattern in prefix {
                 visitor.visit_pat(&subpattern);

compiler/rustc_mir_build/src/build/expr/as_constant.rs

@@ -1,43 +1,141 @@
 //! See docs in build/expr/mod.rs
 
 use crate::build::Builder;
-use rustc_middle::mir::interpret::{ConstValue, Scalar};
+use crate::thir::constant::parse_float;
+use rustc_ast::ast;
+use rustc_hir::def_id::DefId;
+use rustc_middle::mir::interpret::{
+    Allocation, ConstValue, LitToConstError, LitToConstInput, Scalar,
+};
 use rustc_middle::mir::*;
 use rustc_middle::thir::*;
-use rustc_middle::ty::CanonicalUserTypeAnnotation;
+use rustc_middle::ty::subst::SubstsRef;
+use rustc_middle::ty::{self, CanonicalUserTypeAnnotation, Ty, TyCtxt};
+use rustc_target::abi::Size;
 
 impl<'a, 'tcx> Builder<'a, 'tcx> {
     /// Compile `expr`, yielding a compile-time constant. Assumes that
     /// `expr` is a valid compile-time constant!
     crate fn as_constant(&mut self, expr: &Expr<'tcx>) -> Constant<'tcx> {
+        let create_uneval_from_def_id =
+            |tcx: TyCtxt<'tcx>, def_id: DefId, ty: Ty<'tcx>, substs: SubstsRef<'tcx>| {
+                let uneval = ty::Unevaluated::new(ty::WithOptConstParam::unknown(def_id), substs);
+                tcx.mk_const(ty::ConstS { val: ty::ConstKind::Unevaluated(uneval), ty })
+            };
+
         let this = self;
+        let tcx = this.tcx;
         let Expr { ty, temp_lifetime: _, span, ref kind } = *expr;
         match *kind {
             ExprKind::Scope { region_scope: _, lint_level: _, value } => {
                 this.as_constant(&this.thir[value])
             }
-            ExprKind::Literal { literal, user_ty, const_id: _ } => {
+            ExprKind::Literal { lit, neg } => {
+                let literal =
+                    match lit_to_constant(tcx, LitToConstInput { lit: &lit.node, ty, neg }) {
+                        Ok(c) => c,
+                        Err(LitToConstError::Reported) => ConstantKind::Ty(tcx.const_error(ty)),
+                        Err(LitToConstError::TypeError) => {
+                            bug!("encountered type error in `lit_to_constant")
+                        }
+                    };
+
+                Constant { span, user_ty: None, literal: literal.into() }
+            }
+            ExprKind::NonHirLiteral { lit, user_ty } => {
                 let user_ty = user_ty.map(|user_ty| {
                     this.canonical_user_type_annotations.push(CanonicalUserTypeAnnotation {
                         span,
                         user_ty,
                         inferred_ty: ty,
                     })
                 });
-                assert_eq!(literal.ty(), ty);
-                Constant { span, user_ty, literal: literal.into() }
+
+                let literal = ConstantKind::Val(ConstValue::Scalar(Scalar::Int(lit)), ty);
+
+                Constant { span, user_ty: user_ty, literal }
+            }
+            ExprKind::NamedConst { def_id, substs, user_ty } => {
+                let user_ty = user_ty.map(|user_ty| {
+                    this.canonical_user_type_annotations.push(CanonicalUserTypeAnnotation {
+                        span,
+                        user_ty,
+                        inferred_ty: ty,
+                    })
+                });
+                let literal = ConstantKind::Ty(create_uneval_from_def_id(tcx, def_id, ty, substs));
+
+                Constant { user_ty, span, literal }
+            }
+            ExprKind::ConstParam { param, def_id: _ } => {
+                let const_param =
+                    tcx.mk_const(ty::ConstS { val: ty::ConstKind::Param(param), ty: expr.ty });
+                let literal = ConstantKind::Ty(const_param);
+
+                Constant { user_ty: None, span, literal }
+            }
+            ExprKind::ConstBlock { did: def_id, substs } => {
+                let literal = ConstantKind::Ty(create_uneval_from_def_id(tcx, def_id, ty, substs));
+
+                Constant { user_ty: None, span, literal }
             }
             ExprKind::StaticRef { alloc_id, ty, .. } => {
-                let const_val =
-                    ConstValue::Scalar(Scalar::from_pointer(alloc_id.into(), &this.tcx));
+                let const_val = ConstValue::Scalar(Scalar::from_pointer(alloc_id.into(), &tcx));
                 let literal = ConstantKind::Val(const_val, ty);
 
                 Constant { span, user_ty: None, literal }
             }
-            ExprKind::ConstBlock { value } => {
-                Constant { span: span, user_ty: None, literal: value.into() }
-            }
             _ => span_bug!(span, "expression is not a valid constant {:?}", kind),
         }
     }
 }
+
+crate fn lit_to_constant<'tcx>(
+    tcx: TyCtxt<'tcx>,
+    lit_input: LitToConstInput<'tcx>,
+) -> Result<ConstantKind<'tcx>, LitToConstError> {
+    let LitToConstInput { lit, ty, neg } = lit_input;
+    let trunc = |n| {
+        let param_ty = ty::ParamEnv::reveal_all().and(ty);
+        let width = tcx.layout_of(param_ty).map_err(|_| LitToConstError::Reported)?.size;
+        trace!("trunc {} with size {} and shift {}", n, width.bits(), 128 - width.bits());
+        let result = width.truncate(n);
+        trace!("trunc result: {}", result);
+        Ok(ConstValue::Scalar(Scalar::from_uint(result, width)))
+    };
+
+    let value = match (lit, &ty.kind()) {
+        (ast::LitKind::Str(s, _), ty::Ref(_, inner_ty, _)) if inner_ty.is_str() => {
+            let s = s.as_str();
+            let allocation = Allocation::from_bytes_byte_aligned_immutable(s.as_bytes());
+            let allocation = tcx.intern_const_alloc(allocation);
+            ConstValue::Slice { data: allocation, start: 0, end: s.len() }
+        }
+        (ast::LitKind::ByteStr(data), ty::Ref(_, inner_ty, _))
+            if matches!(inner_ty.kind(), ty::Slice(_)) =>
+        {
+            let allocation = Allocation::from_bytes_byte_aligned_immutable(data as &[u8]);
+            let allocation = tcx.intern_const_alloc(allocation);
+            ConstValue::Slice { data: allocation, start: 0, end: data.len() }
+        }
+        (ast::LitKind::ByteStr(data), ty::Ref(_, inner_ty, _)) if inner_ty.is_array() => {
+            let id = tcx.allocate_bytes(data);
+            ConstValue::Scalar(Scalar::from_pointer(id.into(), &tcx))
+        }
+        (ast::LitKind::Byte(n), ty::Uint(ty::UintTy::U8)) => {
+            ConstValue::Scalar(Scalar::from_uint(*n, Size::from_bytes(1)))
+        }
+        (ast::LitKind::Int(n, _), ty::Uint(_)) | (ast::LitKind::Int(n, _), ty::Int(_)) => {
+            trunc(if neg { (*n as i128).overflowing_neg().0 as u128 } else { *n })?
+        }
+        (ast::LitKind::Float(n, _), ty::Float(fty)) => {
+            parse_float(*n, *fty, neg).ok_or(LitToConstError::Reported)?
+        }
+        (ast::LitKind::Bool(b), ty::Bool) => ConstValue::Scalar(Scalar::from_bool(*b)),
+        (ast::LitKind::Char(c), ty::Char) => ConstValue::Scalar(Scalar::from_char(*c)),
+        (ast::LitKind::Err(_), _) => return Err(LitToConstError::Reported),
+        _ => return Err(LitToConstError::TypeError),
+    };
+
+    Ok(ConstantKind::Val(value, ty))
+}

compiler/rustc_mir_build/src/build/expr/as_place.rs

@@ -566,6 +566,9 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
             | ExprKind::Continue { .. }
             | ExprKind::Return { .. }
             | ExprKind::Literal { .. }
+            | ExprKind::NamedConst { .. }
+            | ExprKind::NonHirLiteral { .. }
+            | ExprKind::ConstParam { .. }
             | ExprKind::ConstBlock { .. }
             | ExprKind::StaticRef { .. }
             | ExprKind::InlineAsm { .. }

compiler/rustc_mir_build/src/build/expr/as_rvalue.rs

@@ -327,6 +327,9 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
             }
             ExprKind::Yield { .. }
             | ExprKind::Literal { .. }
+            | ExprKind::NamedConst { .. }
+            | ExprKind::NonHirLiteral { .. }
+            | ExprKind::ConstParam { .. }
             | ExprKind::ConstBlock { .. }
             | ExprKind::StaticRef { .. }
             | ExprKind::Block { .. }

compiler/rustc_mir_build/src/build/expr/as_temp.rs

@@ -70,7 +70,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                     local_decl.local_info =
                         Some(Box::new(LocalInfo::StaticRef { def_id, is_thread_local: true }));
                 }
-                ExprKind::Literal { const_id: Some(def_id), .. } => {
+                ExprKind::NamedConst { def_id, .. } | ExprKind::ConstParam { def_id, .. } => {
                     local_decl.local_info = Some(Box::new(LocalInfo::ConstRef { def_id }));
                 }
                 _ => {}

compiler/rustc_mir_build/src/build/expr/category.rs

@@ -69,9 +69,12 @@ impl Category {
             | ExprKind::AssignOp { .. }
             | ExprKind::ThreadLocalRef(_) => Some(Category::Rvalue(RvalueFunc::AsRvalue)),
 
-            ExprKind::ConstBlock { .. } | ExprKind::Literal { .. } | ExprKind::StaticRef { .. } => {
-                Some(Category::Constant)
-            }
+            ExprKind::ConstBlock { .. }
+            | ExprKind::Literal { .. }
+            | ExprKind::NonHirLiteral { .. }
+            | ExprKind::ConstParam { .. }
+            | ExprKind::StaticRef { .. }
+            | ExprKind::NamedConst { .. } => Some(Category::Constant),
 
             ExprKind::Loop { .. }
             | ExprKind::Block { .. }

compiler/rustc_mir_build/src/build/expr/into.rs

@@ -533,6 +533,9 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
             | ExprKind::Closure { .. }
             | ExprKind::ConstBlock { .. }
             | ExprKind::Literal { .. }
+            | ExprKind::NamedConst { .. }
+            | ExprKind::NonHirLiteral { .. }
+            | ExprKind::ConstParam { .. }
             | ExprKind::ThreadLocalRef(_)
             | ExprKind::StaticRef { .. } => {
                 debug_assert!(match Category::of(&expr.kind).unwrap() {

compiler/rustc_mir_build/src/build/expr/mod.rs

@@ -60,7 +60,7 @@
 //! basically the point where the "by value" operations are bridged
 //! over to the "by reference" mode (`as_place`).
 
-mod as_constant;
+crate mod as_constant;
 mod as_operand;
 pub mod as_place;
 mod as_rvalue;

compiler/rustc_mir_build/src/check_unsafety.rs

@@ -303,6 +303,9 @@ impl<'a, 'tcx> Visitor<'a, 'tcx> for UnsafetyVisitor<'a, 'tcx> {
             | ExprKind::Block { .. }
             | ExprKind::Borrow { .. }
             | ExprKind::Literal { .. }
+            | ExprKind::NamedConst { .. }
+            | ExprKind::NonHirLiteral { .. }
+            | ExprKind::ConstParam { .. }
             | ExprKind::ConstBlock { .. }
             | ExprKind::Deref { .. }
             | ExprKind::Index { .. }

compiler/rustc_mir_build/src/thir/constant.rs

@@ -7,6 +7,7 @@ use rustc_middle::ty::{self, ParamEnv, TyCtxt};
 use rustc_span::symbol::Symbol;
 use rustc_target::abi::Size;
 
+// FIXME Once valtrees are available, get rid of this function and the query
 crate fn lit_to_const<'tcx>(
     tcx: TyCtxt<'tcx>,
     lit_input: LitToConstInput<'tcx>,
@@ -57,7 +58,12 @@ crate fn lit_to_const<'tcx>(
     Ok(ty::Const::from_value(tcx, lit, ty))
 }
 
-fn parse_float<'tcx>(num: Symbol, fty: ty::FloatTy, neg: bool) -> Option<ConstValue<'tcx>> {
+// FIXME move this to rustc_mir_build::build
+pub(crate) fn parse_float<'tcx>(
+    num: Symbol,
+    fty: ty::FloatTy,
+    neg: bool,
+) -> Option<ConstValue<'tcx>> {
     let num = num.as_str();
     use rustc_apfloat::ieee::{Double, Single};
     let scalar = match fty {