Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Factor out niche value computation #2368

Closed
wants to merge 1 commit into from
Closed

Factor out niche value computation #2368

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
31 changes: 13 additions & 18 deletions kani-compiler/src/codegen_cprover_gotoc/codegen/statement.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -16,7 +16,7 @@ use rustc_middle::ty;
use rustc_middle::ty::layout::LayoutOf;
use rustc_middle::ty::{Instance, InstanceDef, Ty};
use rustc_span::Span;
use rustc_target::abi::{FieldsShape, Primitive, TagEncoding, Variants};
use rustc_target::abi::{FieldsShape, TagEncoding, Variants};
use tracing::{debug, debug_span, trace};

impl<'tcx> GotocCtx<'tcx> {
Expand Down Expand Up @@ -88,28 +88,23 @@ impl<'tcx> GotocCtx<'tcx> {
}
TagEncoding::Niche { untagged_variant, niche_variants, niche_start } => {
if untagged_variant != variant_index {
let offset = match &layout.fields {
FieldsShape::Arbitrary { offsets, .. } => offsets[0],
_ => unreachable!("niche encoding must have arbitrary fields"),
};
let discr_ty = self.codegen_enum_discr_typ(pt);
let discr_ty = self.codegen_ty(discr_ty);
let niche_value =
variant_index.as_u32() - niche_variants.start().as_u32();
let niche_value = (niche_value as u128).wrapping_add(*niche_start);
let value = if niche_value == 0
&& matches!(tag.primitive(), Primitive::Pointer(_))
{
discr_ty.null()
} else {
Expr::int_constant(niche_value, discr_ty.clone())
};
let value = self.compute_enum_niche_value(
pt,
variant_index,
tag,
niche_variants,
niche_start,
);
let place = unwrap_or_return_codegen_unimplemented_stmt!(
self,
self.codegen_place(place)
)
.goto_expr;
self.codegen_get_niche(place, offset, discr_ty)
let offset = match &layout.fields {
FieldsShape::Arbitrary { offsets, .. } => offsets[0],
_ => unreachable!("niche encoding must have arbitrary fields"),
};
self.codegen_get_niche(place, offset, value.typ().clone())
.assign(value, location)
} else {
Stmt::skip(location)
Expand Down
27 changes: 26 additions & 1 deletion kani-compiler/src/codegen_cprover_gotoc/codegen/typ.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -20,11 +20,12 @@ use rustc_middle::ty::{
use rustc_middle::ty::{List, TypeFoldable};
use rustc_span::def_id::DefId;
use rustc_target::abi::{
Abi::Vector, FieldsShape, Integer, LayoutS, Primitive, Size, TagEncoding, TyAndLayout,
Abi::Vector, FieldsShape, Integer, LayoutS, Primitive, Scalar, Size, TagEncoding, TyAndLayout,
VariantIdx, Variants,
};
use rustc_target::spec::abi::Abi;
use std::iter;
use std::ops::RangeInclusive;
use tracing::{debug, trace, warn};
use ty::layout::HasParamEnv;

Expand Down Expand Up @@ -1572,6 +1573,30 @@ impl<'tcx> GotocCtx<'tcx> {
}
}

/// Compute the discriminant expression for an enum that uses niche optimization.
///
/// We follow the logic of the SSA and Cranelift back-ends in doing the computation:
/// https://github.com/rust-lang/rust/blob/master/compiler/rustc_codegen_ssa/src/mir/place.rs#L455
/// https://github.com/rust-lang/rust/blob/d37e2f74afd131cda7b08520d37426bfbb622b5c/compiler/rustc_codegen_cranelift/src/discriminant.rs#L52
pub fn compute_enum_niche_value(
&mut self,
enum_ty: Ty<'tcx>,
variant_index: &VariantIdx,
tag: &Scalar,
niche_variants: &RangeInclusive<VariantIdx>,
niche_start: &u128,
) -> Expr {
let discr_ty = self.codegen_enum_discr_typ(enum_ty);
let discr_ty = self.codegen_ty(discr_ty);
let niche_value = variant_index.as_u32() - niche_variants.start().as_u32();
let niche_value = (niche_value as u128).wrapping_add(*niche_start);
if niche_value == 0 && matches!(tag.primitive(), Primitive::Pointer(_)) {
discr_ty.null()
} else {
Expr::int_constant(niche_value, discr_ty.clone())
}
}

pub(crate) fn variant_min_offset(
&self,
variants: &IndexVec<VariantIdx, LayoutS<VariantIdx>>,
Expand Down