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Do not materialise X in [X; 0] when X is unsizing a const #145277
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dingxiangfei2009
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
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@@ -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}; | ||
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@@ -656,6 +657,27 @@ impl<'a, 'tcx> Builder<'a, 'tcx> { | |
| block.and(rvalue) | ||
| } | ||
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| /// Recursively inspect a THIR expression and probe through unsizing | ||
| /// operations that can be const-folded today. | ||
|
There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. What does this have to do with const-folding (which usually refers to the constant propagation optimization pass)? |
||
| 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)), | ||
| } | ||
| } | ||
| } | ||
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| fn build_zero_repeat( | ||
| &mut self, | ||
| mut block: BasicBlock, | ||
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@@ -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` | ||
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46 changes: 46 additions & 0 deletions
tests/ui/coercion/no_local_for_coerced_const-issue-143671.rs
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,46 @@ | ||
| //@ run-pass | ||
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| #![feature(unsize)] | ||
| #![feature(coerce_unsized)] | ||
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| use std::fmt::Display; | ||
| use std::marker::Unsize; | ||
| use std::ops::CoerceUnsized; | ||
| use std::rc::Weak; | ||
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| #[repr(transparent)] | ||
| struct X<'a, T: ?Sized> { | ||
| f: &'a T, | ||
| } | ||
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| impl<'a, T: ?Sized> Drop for X<'a, T> { | ||
| fn drop(&mut self) { | ||
| panic!() | ||
| } | ||
| } | ||
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| impl<'a, T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<X<'a, U>> for X<'a, T> where | ||
| &'a T: CoerceUnsized<&'a U> | ||
| { | ||
| } | ||
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| const Y: X<'static, i32> = X { f: &0 }; | ||
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| fn main() { | ||
| let _: [X<'static, dyn Display>; 0] = [Y; 0]; | ||
| coercion_on_weak_in_const(); | ||
| coercion_on_weak_as_cast(); | ||
| } | ||
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| fn coercion_on_weak_in_const() { | ||
| const X: Weak<i32> = Weak::new(); | ||
| const Y: [Weak<dyn Send>; 0] = [X; 0]; | ||
| let _ = Y; | ||
| } | ||
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| fn coercion_on_weak_as_cast() { | ||
| const Y: X<'static, i32> = X { f: &0 }; | ||
| // What happens in the following code is that | ||
| // a constant is explicitly coerced into | ||
| let _a: [X<'static, dyn Display>; 0] = [Y as X<'static, dyn Display>; 0]; | ||
| } |
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