bjoernager/rust
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Auto merge of #111913 - oli-obk:valtrees2, r=lcnr

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Only rewrite valtree-constants to patterns and keep other constants opaque

Now that we can reliably fall back to comparing constants with `PartialEq::eq` to the match scrutinee, we can

1. eagerly try to convert constants to valtrees
2. then deeply convert the valtree to a pattern
3. if the to-valtree conversion failed, create an "opaque constant" pattern.

This PR specifically avoids any behavioral changes or major cleanups. What we can now do as follow ups is

* move the two remaining call sites to `destructure_mir_constant` off that query
* make valtree to pattern conversion infallible
    * this needs to be done after careful analysis of the effects. There may be user visible changes from that.

based on https://github.com/rust-lang/rust/pull/111768
This commit is contained in:
bors 2023-05-31 16:36:51 +00:00
commit 871b595202
21 changed files with 300 additions and 323 deletions
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39
compiler/rustc_const_eval/src/const_eval/mod.rs
View file

@ -2,10 +2,8 @@
use crate::errors::MaxNumNodesInConstErr;
use crate::interpret::{
intern_const_alloc_recursive, ConstValue, InternKind, InterpCx, InterpResult, MemPlaceMeta,
Scalar,
intern_const_alloc_recursive, ConstValue, InternKind, InterpCx, InterpResult, Scalar,
};
use rustc_hir::Mutability;
use rustc_middle::mir;
use rustc_middle::mir::interpret::{EvalToValTreeResult, GlobalId};
use rustc_middle::ty::{self, TyCtxt};
@ -131,38 +129,3 @@ pub(crate) fn try_destructure_mir_constant<'tcx>(
Ok(mir::DestructuredConstant { variant, fields })
}
#[instrument(skip(tcx), level = "debug")]
pub(crate) fn deref_mir_constant<'tcx>(
tcx: TyCtxt<'tcx>,
param_env: ty::ParamEnv<'tcx>,
val: mir::ConstantKind<'tcx>,
) -> mir::ConstantKind<'tcx> {
let ecx = mk_eval_cx(tcx, DUMMY_SP, param_env, false);
let op = ecx.eval_mir_constant(&val, None, None).unwrap();
let mplace = ecx.deref_operand(&op).unwrap();
if let Some(alloc_id) = mplace.ptr.provenance {
assert_eq!(
tcx.global_alloc(alloc_id).unwrap_memory().0.0.mutability,
Mutability::Not,
"deref_mir_constant cannot be used with mutable allocations as \
that could allow pattern matching to observe mutable statics",
);
}
let ty = match mplace.meta {
MemPlaceMeta::None => mplace.layout.ty,
// In case of unsized types, figure out the real type behind.
MemPlaceMeta::Meta(scalar) => match mplace.layout.ty.kind() {
ty::Str => bug!("there's no sized equivalent of a `str`"),
ty::Slice(elem_ty) => tcx.mk_array(*elem_ty, scalar.to_target_usize(&tcx).unwrap()),
_ => bug!(
"type {} should not have metadata, but had {:?}",
mplace.layout.ty,
mplace.meta
),
},
};
mir::ConstantKind::Val(op_to_const(&ecx, &mplace.into()), ty)
}

4
compiler/rustc_const_eval/src/lib.rs
View file

@ -56,10 +56,6 @@ pub fn provide(providers: &mut Providers) {
providers.valtree_to_const_val = |tcx, (ty, valtree)| {
const_eval::valtree_to_const_value(tcx, ty::ParamEnv::empty().and(ty), valtree)
};
providers.deref_mir_constant = |tcx, param_env_and_value| {
let (param_env, value) = param_env_and_value.into_parts();
const_eval::deref_mir_constant(tcx, param_env, value)
};
providers.check_validity_requirement = |tcx, (init_kind, param_env_and_ty)| {
util::check_validity_requirement(tcx, init_kind, param_env_and_ty)
};