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Auto merge of #83207 - oli-obk:valtree2, r=lcnr

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normalize mir::Constant differently from ty::Const in preparation for valtrees

Valtrees are unable to represent many kind of constant values (this is on purpose). For constants that are used at runtime, we do not need a valtree representation and can thus use a different form of evaluation. In order to make this explicit and less fragile, I added a `fold_constant` method to `TypeFolder` and implemented it for normalization. Normalization can now, when it wants to eagerly evaluate a constant, normalize `mir::Constant` directly into a `mir::ConstantKind::Val` instead of relying on the `ty::Const` evaluation.

In the future we can get rid of the `ty::Const` in there entirely and add our own `Unevaluated` variant to `mir::ConstantKind`. This would allow us to remove the `promoted` field from `ty::ConstKind::Unevaluated`, as promoteds can never occur in the type system.

cc `@rust-lang/wg-const-eval`

r? `@lcnr`
This commit is contained in:
bors 2021-04-02 10:28:12 +00:00
commit 0978a9eb99
41 changed files with 183 additions and 55 deletions
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11
compiler/rustc_middle/src/mir/mod.rs
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@ -2392,7 +2392,8 @@ pub struct Constant<'tcx> {
pub literal: ConstantKind<'tcx>,
}
#[derive(Clone, Copy, PartialEq, PartialOrd, TyEncodable, TyDecodable, Hash, HashStable, Debug)]
#[derive(Clone, Copy, PartialEq, Eq, PartialOrd, TyEncodable, TyDecodable, Hash, HashStable, Debug)]
#[derive(Lift)]
pub enum ConstantKind<'tcx> {
/// This constant came from the type system
Ty(&'tcx ty::Const<'tcx>),
@ -2691,7 +2692,13 @@ impl<'tcx> Display for Constant<'tcx> {
ty::FnDef(..) => {}
_ => write!(fmt, "const ")?,
}
match self.literal {
Display::fmt(&self.literal, fmt)
}
}
impl<'tcx> Display for ConstantKind<'tcx> {
fn fmt(&self, fmt: &mut Formatter<'_>) -> fmt::Result {
match *self {
ConstantKind::Ty(c) => pretty_print_const(c, fmt, true),
ConstantKind::Val(val, ty) => pretty_print_const_value(val, ty, fmt, true),
}