diff options
Diffstat (limited to 'compiler/rustc_mir_build/src/build/expr/as_constant.rs')
| -rw-r--r-- | compiler/rustc_mir_build/src/build/expr/as_constant.rs | 152 |
1 files changed, 152 insertions, 0 deletions
diff --git a/compiler/rustc_mir_build/src/build/expr/as_constant.rs b/compiler/rustc_mir_build/src/build/expr/as_constant.rs new file mode 100644 index 000000000..648d10b9e --- /dev/null +++ b/compiler/rustc_mir_build/src/build/expr/as_constant.rs @@ -0,0 +1,152 @@ +//! See docs in build/expr/mod.rs + +use crate::build::{parse_float_into_constval, Builder}; +use rustc_ast as ast; +use rustc_hir::def_id::DefId; +use rustc_middle::mir::interpret::{ + Allocation, ConstValue, LitToConstError, LitToConstInput, Scalar, +}; +use rustc_middle::mir::*; +use rustc_middle::thir::*; +use rustc_middle::ty::subst::SubstsRef; +use rustc_middle::ty::{self, CanonicalUserTypeAnnotation, Ty, TyCtxt}; +use rustc_target::abi::Size; + +impl<'a, 'tcx> Builder<'a, 'tcx> { + /// Compile `expr`, yielding a compile-time constant. Assumes that + /// `expr` is a valid compile-time constant! + pub(crate) fn as_constant(&mut self, expr: &Expr<'tcx>) -> Constant<'tcx> { + let create_uneval_from_def_id = + |tcx: TyCtxt<'tcx>, def_id: DefId, ty: Ty<'tcx>, substs: SubstsRef<'tcx>| { + let uneval = ty::Unevaluated::new(ty::WithOptConstParam::unknown(def_id), substs); + tcx.mk_const(ty::ConstS { kind: ty::ConstKind::Unevaluated(uneval), ty }) + }; + + let this = self; + let tcx = this.tcx; + let Expr { ty, temp_lifetime: _, span, ref kind } = *expr; + match *kind { + ExprKind::Scope { region_scope: _, lint_level: _, value } => { + this.as_constant(&this.thir[value]) + } + ExprKind::Literal { lit, neg } => { + let literal = + match lit_to_mir_constant(tcx, LitToConstInput { lit: &lit.node, ty, neg }) { + Ok(c) => c, + Err(LitToConstError::Reported) => ConstantKind::Ty(tcx.const_error(ty)), + Err(LitToConstError::TypeError) => { + bug!("encountered type error in `lit_to_mir_constant") + } + }; + + Constant { span, user_ty: None, literal } + } + ExprKind::NonHirLiteral { lit, user_ty } => { + let user_ty = user_ty.map(|user_ty| { + this.canonical_user_type_annotations.push(CanonicalUserTypeAnnotation { + span, + user_ty, + inferred_ty: ty, + }) + }); + let literal = ConstantKind::Val(ConstValue::Scalar(Scalar::Int(lit)), ty); + + Constant { span, user_ty: user_ty, literal } + } + ExprKind::ZstLiteral { user_ty } => { + let user_ty = user_ty.map(|user_ty| { + this.canonical_user_type_annotations.push(CanonicalUserTypeAnnotation { + span, + user_ty, + inferred_ty: ty, + }) + }); + let literal = ConstantKind::Val(ConstValue::ZeroSized, ty); + + Constant { span, user_ty: user_ty, literal } + } + ExprKind::NamedConst { def_id, substs, user_ty } => { + let user_ty = user_ty.map(|user_ty| { + this.canonical_user_type_annotations.push(CanonicalUserTypeAnnotation { + span, + user_ty, + inferred_ty: ty, + }) + }); + let literal = ConstantKind::Ty(create_uneval_from_def_id(tcx, def_id, ty, substs)); + + Constant { user_ty, span, literal } + } + ExprKind::ConstParam { param, def_id: _ } => { + let const_param = + tcx.mk_const(ty::ConstS { kind: ty::ConstKind::Param(param), ty: expr.ty }); + let literal = ConstantKind::Ty(const_param); + + Constant { user_ty: None, span, literal } + } + ExprKind::ConstBlock { did: def_id, substs } => { + let literal = ConstantKind::Ty(create_uneval_from_def_id(tcx, def_id, ty, substs)); + + Constant { user_ty: None, span, literal } + } + ExprKind::StaticRef { alloc_id, ty, .. } => { + let const_val = ConstValue::Scalar(Scalar::from_pointer(alloc_id.into(), &tcx)); + let literal = ConstantKind::Val(const_val, ty); + + Constant { span, user_ty: None, literal } + } + _ => span_bug!(span, "expression is not a valid constant {:?}", kind), + } + } +} + +#[instrument(skip(tcx, lit_input))] +pub(crate) fn lit_to_mir_constant<'tcx>( + tcx: TyCtxt<'tcx>, + lit_input: LitToConstInput<'tcx>, +) -> Result<ConstantKind<'tcx>, LitToConstError> { + let LitToConstInput { lit, ty, neg } = lit_input; + let trunc = |n| { + let param_ty = ty::ParamEnv::reveal_all().and(ty); + let width = tcx.layout_of(param_ty).map_err(|_| LitToConstError::Reported)?.size; + trace!("trunc {} with size {} and shift {}", n, width.bits(), 128 - width.bits()); + let result = width.truncate(n); + trace!("trunc result: {}", result); + Ok(ConstValue::Scalar(Scalar::from_uint(result, width))) + }; + + let value = match (lit, &ty.kind()) { + (ast::LitKind::Str(s, _), ty::Ref(_, inner_ty, _)) if inner_ty.is_str() => { + let s = s.as_str(); + let allocation = Allocation::from_bytes_byte_aligned_immutable(s.as_bytes()); + let allocation = tcx.intern_const_alloc(allocation); + ConstValue::Slice { data: allocation, start: 0, end: s.len() } + } + (ast::LitKind::ByteStr(data), ty::Ref(_, inner_ty, _)) + if matches!(inner_ty.kind(), ty::Slice(_)) => + { + let allocation = Allocation::from_bytes_byte_aligned_immutable(data as &[u8]); + let allocation = tcx.intern_const_alloc(allocation); + ConstValue::Slice { data: allocation, start: 0, end: data.len() } + } + (ast::LitKind::ByteStr(data), ty::Ref(_, inner_ty, _)) if inner_ty.is_array() => { + let id = tcx.allocate_bytes(data); + ConstValue::Scalar(Scalar::from_pointer(id.into(), &tcx)) + } + (ast::LitKind::Byte(n), ty::Uint(ty::UintTy::U8)) => { + ConstValue::Scalar(Scalar::from_uint(*n, Size::from_bytes(1))) + } + (ast::LitKind::Int(n, _), ty::Uint(_)) | (ast::LitKind::Int(n, _), ty::Int(_)) => { + trunc(if neg { (*n as i128).overflowing_neg().0 as u128 } else { *n })? + } + (ast::LitKind::Float(n, _), ty::Float(fty)) => { + parse_float_into_constval(*n, *fty, neg).ok_or(LitToConstError::Reported)? + } + (ast::LitKind::Bool(b), ty::Bool) => ConstValue::Scalar(Scalar::from_bool(*b)), + (ast::LitKind::Char(c), ty::Char) => ConstValue::Scalar(Scalar::from_char(*c)), + (ast::LitKind::Err(_), _) => return Err(LitToConstError::Reported), + _ => return Err(LitToConstError::TypeError), + }; + + Ok(ConstantKind::Val(value, ty)) +} |