Lower inline const down to MIR

compiler/rustc_hir/src/hir.rs

@@ -1361,6 +1361,7 @@ impl Expr<'_> {
     pub fn precedence(&self) -> ExprPrecedence {
         match self.kind {
             ExprKind::Box(_) => ExprPrecedence::Box,
+            ExprKind::ConstBlock(_) => ExprPrecedence::ConstBlock,
             ExprKind::Array(_) => ExprPrecedence::Array,
             ExprKind::Call(..) => ExprPrecedence::Call,
             ExprKind::MethodCall(..) => ExprPrecedence::MethodCall,
@@ -1446,6 +1447,7 @@ impl Expr<'_> {
             | ExprKind::LlvmInlineAsm(..)
             | ExprKind::AssignOp(..)
             | ExprKind::Lit(_)
+            | ExprKind::ConstBlock(..)
             | ExprKind::Unary(..)
             | ExprKind::Box(..)
             | ExprKind::AddrOf(..)
@@ -1501,6 +1503,8 @@ pub fn is_range_literal(expr: &Expr<'_>) -> bool {
 pub enum ExprKind<'hir> {
     /// A `box x` expression.
     Box(&'hir Expr<'hir>),
+    /// Allow anonymous constants from an inline `const` block
+    ConstBlock(AnonConst),
     /// An array (e.g., `[a, b, c, d]`).
     Array(&'hir [Expr<'hir>]),
     /// A function call.

compiler/rustc_hir/src/intravisit.rs

@@ -1068,6 +1068,7 @@ pub fn walk_expr<'v, V: Visitor<'v>>(visitor: &mut V, expression: &'v Expr<'v>)
         ExprKind::Array(subexpressions) => {
             walk_list!(visitor, visit_expr, subexpressions);
         }
+        ExprKind::ConstBlock(ref anon_const) => visitor.visit_anon_const(anon_const),
         ExprKind::Repeat(ref element, ref count) => {
             visitor.visit_expr(element);
             visitor.visit_anon_const(count)

compiler/rustc_hir_pretty/src/lib.rs

@@ -1135,6 +1135,15 @@ impl<'a> State<'a> {
         self.end()
     }
 
+    fn print_expr_anon_const(&mut self, anon_const: &hir::AnonConst) {
+        self.ibox(INDENT_UNIT);
+        self.s.word_space("const");
+        self.s.word("{");
+        self.print_anon_const(anon_const);
+        self.s.word("}");
+        self.end()
+    }
+
     fn print_expr_repeat(&mut self, element: &hir::Expr<'_>, count: &hir::AnonConst) {
         self.ibox(INDENT_UNIT);
         self.s.word("[");
@@ -1287,6 +1296,9 @@ impl<'a> State<'a> {
             hir::ExprKind::Array(ref exprs) => {
                 self.print_expr_vec(exprs);
             }
+            hir::ExprKind::ConstBlock(ref anon_const) => {
+                self.print_expr_anon_const(anon_const);
+            }
             hir::ExprKind::Repeat(ref element, ref count) => {
                 self.print_expr_repeat(&element, count);
             }

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

@@ -33,6 +33,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                 Constant { span, user_ty, literal }
             }
             ExprKind::StaticRef { literal, .. } => Constant { span, user_ty: None, literal },
+            ExprKind::ConstBlock { value } => Constant { span, user_ty: None, literal: value },
             _ => span_bug!(span, "expression is not a valid constant {:?}", kind),
         }
     }

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

@@ -254,6 +254,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
             | ExprKind::Continue { .. }
             | ExprKind::Return { .. }
             | ExprKind::Literal { .. }
+            | ExprKind::ConstBlock { .. }
             | ExprKind::StaticRef { .. }
             | ExprKind::InlineAsm { .. }
             | ExprKind::LlvmInlineAsm { .. }

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

@@ -234,6 +234,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
             }
             ExprKind::Yield { .. }
             | ExprKind::Literal { .. }
+            | ExprKind::ConstBlock { .. }
             | ExprKind::StaticRef { .. }
             | ExprKind::Block { .. }
             | ExprKind::Match { .. }

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

@@ -68,7 +68,9 @@ impl Category {
             | ExprKind::ThreadLocalRef(_)
             | ExprKind::LlvmInlineAsm { .. } => Some(Category::Rvalue(RvalueFunc::AsRvalue)),
 
-            ExprKind::Literal { .. } | ExprKind::StaticRef { .. } => Some(Category::Constant),
+            ExprKind::ConstBlock { .. } | ExprKind::Literal { .. } | ExprKind::StaticRef { .. } => {
+                Some(Category::Constant)
+            }
 
             ExprKind::Loop { .. }
             | ExprKind::Block { .. }

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

@@ -454,6 +454,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
             | ExprKind::Array { .. }
             | ExprKind::Tuple { .. }
             | ExprKind::Closure { .. }
+            | ExprKind::ConstBlock { .. }
             | ExprKind::Literal { .. }
             | ExprKind::ThreadLocalRef(_)
             | ExprKind::StaticRef { .. } => {

compiler/rustc_mir_build/src/thir/cx/expr.rs

@@ -511,6 +511,12 @@ fn make_mirror_unadjusted<'a, 'tcx>(
             inputs: asm.inputs_exprs.to_ref(),
         },
 
+        hir::ExprKind::ConstBlock(ref anon_const) => {
+            let anon_const_def_id = cx.tcx.hir().local_def_id(anon_const.hir_id);
+            let value = ty::Const::from_anon_const(cx.tcx, anon_const_def_id);
+
+            ExprKind::ConstBlock { value }
+        }
         // Now comes the rote stuff:
         hir::ExprKind::Repeat(ref v, ref count) => {
             let count_def_id = cx.tcx.hir().local_def_id(count.hir_id);

compiler/rustc_mir_build/src/thir/mod.rs

@@ -232,6 +232,9 @@ crate enum ExprKind<'tcx> {
     Return {
         value: Option<ExprRef<'tcx>>,
     },
+    ConstBlock {
+        value: &'tcx Const<'tcx>,
+    },
     Repeat {
         value: ExprRef<'tcx>,
         count: &'tcx Const<'tcx>,

compiler/rustc_mir_build/src/thir/pattern/mod.rs

@@ -856,6 +856,11 @@ impl<'a, 'tcx> PatCtxt<'a, 'tcx> {
             *self.lower_path(qpath, expr.hir_id, expr.span).kind
         } else {
             let (lit, neg) = match expr.kind {
+                hir::ExprKind::ConstBlock(ref anon_const) => {
+                    let anon_const_def_id = self.tcx.hir().local_def_id(anon_const.hir_id);
+                    let value = ty::Const::from_anon_const(self.tcx, anon_const_def_id);
+                    return *self.const_to_pat(value, expr.hir_id, expr.span, false).kind;
+                }
                 hir::ExprKind::Lit(ref lit) => (lit, false),
                 hir::ExprKind::Unary(hir::UnOp::UnNeg, ref expr) => {
                     let lit = match expr.kind {

compiler/rustc_passes/src/liveness.rs

@@ -432,6 +432,7 @@ impl<'tcx> Visitor<'tcx> for IrMaps<'tcx> {
             | hir::ExprKind::Break(..)
             | hir::ExprKind::Continue(_)
             | hir::ExprKind::Lit(_)
+            | hir::ExprKind::ConstBlock(..)
             | hir::ExprKind::Ret(..)
             | hir::ExprKind::Block(..)
             | hir::ExprKind::Assign(..)
@@ -1232,6 +1233,7 @@ impl<'a, 'tcx> Liveness<'a, 'tcx> {
             }
 
             hir::ExprKind::Lit(..)
+            | hir::ExprKind::ConstBlock(..)
             | hir::ExprKind::Err
             | hir::ExprKind::Path(hir::QPath::TypeRelative(..))
             | hir::ExprKind::Path(hir::QPath::LangItem(..)) => succ,
@@ -1478,6 +1480,7 @@ fn check_expr<'tcx>(this: &mut Liveness<'_, 'tcx>, expr: &'tcx Expr<'tcx>) {
         | hir::ExprKind::Break(..)
         | hir::ExprKind::Continue(..)
         | hir::ExprKind::Lit(_)
+        | hir::ExprKind::ConstBlock(..)
         | hir::ExprKind::Block(..)
         | hir::ExprKind::AddrOf(..)
         | hir::ExprKind::Struct(..)