1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
//! See docs in build/expr/mod.rs

use rustc_ast as ast;
use rustc_hir::LangItem;
use rustc_middle::mir::interpret::{
    Allocation, LitToConstError, LitToConstInput, Scalar, CTFE_ALLOC_SALT,
};
use rustc_middle::mir::*;
use rustc_middle::thir::*;
use rustc_middle::ty::{
    self, CanonicalUserType, CanonicalUserTypeAnnotation, Ty, TyCtxt, UserTypeAnnotationIndex,
};
use rustc_middle::{bug, mir, span_bug};
use rustc_target::abi::Size;
use tracing::{instrument, trace};

use crate::build::{parse_float_into_constval, Builder};

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>) -> ConstOperand<'tcx> {
        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])
            }
            _ => as_constant_inner(
                expr,
                |user_ty| {
                    Some(this.canonical_user_type_annotations.push(CanonicalUserTypeAnnotation {
                        span,
                        user_ty: user_ty.clone(),
                        inferred_ty: ty,
                    }))
                },
                tcx,
            ),
        }
    }
}

pub(crate) fn as_constant_inner<'tcx>(
    expr: &Expr<'tcx>,
    push_cuta: impl FnMut(&Box<CanonicalUserType<'tcx>>) -> Option<UserTypeAnnotationIndex>,
    tcx: TyCtxt<'tcx>,
) -> ConstOperand<'tcx> {
    let Expr { ty, temp_lifetime: _, span, ref kind } = *expr;
    match *kind {
        ExprKind::Literal { lit, neg } => {
            let const_ = match lit_to_mir_constant(tcx, LitToConstInput { lit: &lit.node, ty, neg })
            {
                Ok(c) => c,
                Err(LitToConstError::Reported(guar)) => {
                    Const::Ty(Ty::new_error(tcx, guar), ty::Const::new_error(tcx, guar))
                }
                Err(LitToConstError::TypeError) => {
                    bug!("encountered type error in `lit_to_mir_constant`")
                }
            };

            ConstOperand { span, user_ty: None, const_ }
        }
        ExprKind::NonHirLiteral { lit, ref user_ty } => {
            let user_ty = user_ty.as_ref().and_then(push_cuta);

            let const_ = Const::Val(ConstValue::Scalar(Scalar::Int(lit)), ty);

            ConstOperand { span, user_ty, const_ }
        }
        ExprKind::ZstLiteral { ref user_ty } => {
            let user_ty = user_ty.as_ref().and_then(push_cuta);

            let const_ = Const::Val(ConstValue::ZeroSized, ty);

            ConstOperand { span, user_ty, const_ }
        }
        ExprKind::NamedConst { def_id, args, ref user_ty } => {
            let user_ty = user_ty.as_ref().and_then(push_cuta);

            let uneval = mir::UnevaluatedConst::new(def_id, args);
            let const_ = Const::Unevaluated(uneval, ty);

            ConstOperand { user_ty, span, const_ }
        }
        ExprKind::ConstParam { param, def_id: _ } => {
            let const_param = ty::Const::new_param(tcx, param);
            let const_ = Const::Ty(expr.ty, const_param);

            ConstOperand { user_ty: None, span, const_ }
        }
        ExprKind::ConstBlock { did: def_id, args } => {
            let uneval = mir::UnevaluatedConst::new(def_id, args);
            let const_ = Const::Unevaluated(uneval, ty);

            ConstOperand { user_ty: None, span, const_ }
        }
        ExprKind::StaticRef { alloc_id, ty, .. } => {
            let const_val = ConstValue::Scalar(Scalar::from_pointer(alloc_id.into(), &tcx));
            let const_ = Const::Val(const_val, ty);

            ConstOperand { span, user_ty: None, const_ }
        }
        _ => span_bug!(span, "expression is not a valid constant {:?}", kind),
    }
}

#[instrument(skip(tcx, lit_input))]
fn lit_to_mir_constant<'tcx>(
    tcx: TyCtxt<'tcx>,
    lit_input: LitToConstInput<'tcx>,
) -> Result<Const<'tcx>, LitToConstError> {
    let LitToConstInput { lit, ty, neg } = lit_input;
    let trunc = |n| {
        let param_ty = ty::ParamEnv::reveal_all().and(ty);
        let width = match tcx.layout_of(param_ty) {
            Ok(layout) => layout.size,
            Err(_) => {
                tcx.dcx().bug(format!("couldn't compute width of literal: {:?}", lit_input.lit))
            }
        };
        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.mk_const_alloc(allocation);
            ConstValue::Slice { data: allocation, meta: allocation.inner().size().bytes() }
        }
        (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.mk_const_alloc(allocation);
            ConstValue::Slice { data: allocation, meta: allocation.inner().size().bytes() }
        }
        (ast::LitKind::ByteStr(data, _), ty::Ref(_, inner_ty, _)) if inner_ty.is_array() => {
            let id = tcx.allocate_bytes_dedup(data, CTFE_ALLOC_SALT);
            ConstValue::Scalar(Scalar::from_pointer(id.into(), &tcx))
        }
        (ast::LitKind::CStr(data, _), ty::Ref(_, inner_ty, _)) if matches!(inner_ty.kind(), ty::Adt(def, _) if tcx.is_lang_item(def.did(), LangItem::CStr)) =>
        {
            let allocation = Allocation::from_bytes_byte_aligned_immutable(data as &[u8]);
            let allocation = tcx.mk_const_alloc(allocation);
            ConstValue::Slice { data: allocation, meta: allocation.inner().size().bytes() }
        }
        (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.get() as i128).overflowing_neg().0 as u128 } else { n.get() })?
        }
        (ast::LitKind::Float(n, _), ty::Float(fty)) => parse_float_into_constval(*n, *fty, neg)
            .ok_or_else(|| {
                LitToConstError::Reported(
                    tcx.dcx()
                        .delayed_bug(format!("couldn't parse float literal: {:?}", lit_input.lit)),
                )
            })?,
        (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(guar), _) => return Err(LitToConstError::Reported(*guar)),
        _ => return Err(LitToConstError::TypeError),
    };

    Ok(Const::Val(value, ty))
}