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Rollup merge of #78351 - RalfJung:validity-unsafe-cell, r=oli-obk

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Move "mutable thing in const" check from interning to validity

This moves the check for mutable things (such as `UnsafeCell` or `&mut`) in a`const` from interning to validity. That means we can give more targeted error messages (pointing out *where* the problem lies), and we can simplify interning a bit.

Also fix the interning mode used for promoteds in statics.

r? @oli-obk
This commit is contained in:
Dylan DPC 2020-10-28 01:21:18 +01:00 • committed by GitHub
commit 54ea0f9ccd
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10 changed files with 135 additions and 144 deletions
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12
compiler/rustc_middle/src/mir/mod.rs
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@ -210,16 +210,6 @@ pub struct Body<'tcx> {
/// We hold in this field all the constants we are not able to evaluate yet.
pub required_consts: Vec<Constant<'tcx>>,
/// The user may be writing e.g. `&[(SOME_CELL, 42)][i].1` and this would get promoted, because
/// we'd statically know that no thing with interior mutability will ever be available to the
/// user without some serious unsafe code. Now this means that our promoted is actually
/// `&[(SOME_CELL, 42)]` and the MIR using it will do the `&promoted[i].1` projection because
/// the index may be a runtime value. Such a promoted value is illegal because it has reachable
/// interior mutability. This flag just makes this situation very obvious where the previous
/// implementation without the flag hid this situation silently.
/// FIXME(oli-obk): rewrite the promoted during promotion to eliminate the cell components.
pub ignore_interior_mut_in_const_validation: bool,
/// Does this body use generic parameters. This is used for the `ConstEvaluatable` check.
///
/// Note that this does not actually mean that this body is not computable right now.
@ -276,7 +266,6 @@ impl<'tcx> Body<'tcx> {
var_debug_info,
span,
required_consts: Vec::new(),
ignore_interior_mut_in_const_validation: false,
is_polymorphic: false,
predecessor_cache: PredecessorCache::new(),
};
@ -306,7 +295,6 @@ impl<'tcx> Body<'tcx> {
required_consts: Vec::new(),
generator_kind: None,
var_debug_info: Vec::new(),
ignore_interior_mut_in_const_validation: false,
is_polymorphic: false,
predecessor_cache: PredecessorCache::new(),
};