diff options
Diffstat (limited to 'compiler')
| -rw-r--r-- | compiler/rustc_mir_build/src/builder/expr/as_rvalue.rs | 24 |
1 files changed, 23 insertions, 1 deletions
diff --git a/compiler/rustc_mir_build/src/builder/expr/as_rvalue.rs b/compiler/rustc_mir_build/src/builder/expr/as_rvalue.rs index a4ef6e92739..3a5839f2d40 100644 --- a/compiler/rustc_mir_build/src/builder/expr/as_rvalue.rs +++ b/compiler/rustc_mir_build/src/builder/expr/as_rvalue.rs @@ -8,6 +8,7 @@ use rustc_middle::middle::region; use rustc_middle::mir::interpret::Scalar; use rustc_middle::mir::*; use rustc_middle::thir::*; +use rustc_middle::ty::adjustment::PointerCoercion; use rustc_middle::ty::cast::{CastTy, mir_cast_kind}; use rustc_middle::ty::util::IntTypeExt; use rustc_middle::ty::{self, Ty, UpvarArgs}; @@ -656,6 +657,27 @@ impl<'a, 'tcx> Builder<'a, 'tcx> { block.and(rvalue) } + /// Recursively inspect a THIR expression and probe through unsizing + /// operations that can be const-folded today. + fn check_constness(&self, mut kind: &'a ExprKind<'tcx>) -> bool { + loop { + debug!(?kind, "check_constness"); + match kind { + &ExprKind::ValueTypeAscription { source: eid, user_ty: _, user_ty_span: _ } + | &ExprKind::Use { source: eid } + | &ExprKind::PointerCoercion { + cast: PointerCoercion::Unsize, + source: eid, + is_from_as_cast: _, + } + | &ExprKind::Scope { region_scope: _, lint_level: _, value: eid } => { + kind = &self.thir[eid].kind + } + _ => return matches!(Category::of(&kind), Some(Category::Constant)), + } + } + } + fn build_zero_repeat( &mut self, mut block: BasicBlock, @@ -666,7 +688,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> { let this = self; let value_expr = &this.thir[value]; let elem_ty = value_expr.ty; - if let Some(Category::Constant) = Category::of(&value_expr.kind) { + if this.check_constness(&value_expr.kind) { // Repeating a const does nothing } else { // For a non-const, we may need to generate an appropriate `Drop` |