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

use crate::errors;
use crate::mir::operand::OperandRef;
use crate::traits::*;
use rustc_middle::mir;
use rustc_middle::mir::interpret::{ConstValue, ErrorHandled};
use rustc_middle::ty::layout::HasTyCtxt;
use rustc_middle::ty::{self, Ty};
use rustc_target::abi::Abi;

use super::FunctionCx;

impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
    pub fn eval_mir_constant_to_operand(
        &self,
        bx: &mut Bx,
        constant: &mir::Constant<'tcx>,
    ) -> Result<OperandRef<'tcx, Bx::Value>, ErrorHandled> {
        let val = self.eval_mir_constant(constant)?;
        let ty = self.monomorphize(constant.ty());
        Ok(OperandRef::from_const(bx, val, ty))
    }

    pub fn eval_mir_constant(
        &self,
        constant: &mir::Constant<'tcx>,
    ) -> Result<ConstValue<'tcx>, ErrorHandled> {
        let ct = self.monomorphize(constant.literal);
        let uv = match ct {
            mir::ConstantKind::Ty(ct) => match ct.kind() {
                ty::ConstKind::Unevaluated(uv) => uv.expand(),
                ty::ConstKind::Value(val) => {
                    return Ok(self.cx.tcx().valtree_to_const_val((ct.ty(), val)));
                }
                err => span_bug!(
                    constant.span,
                    "encountered bad ConstKind after monomorphizing: {:?}",
                    err
                ),
            },
            mir::ConstantKind::Unevaluated(uv, _) => uv,
            mir::ConstantKind::Val(val, _) => return Ok(val),
        };

        self.cx.tcx().const_eval_resolve(ty::ParamEnv::reveal_all(), uv, None).map_err(|err| {
            match err {
                ErrorHandled::Reported(_) => {
                    self.cx.tcx().sess.emit_err(errors::ErroneousConstant { span: constant.span });
                }
                ErrorHandled::TooGeneric => {
                    self.cx
                        .tcx()
                        .sess
                        .diagnostic()
                        .emit_bug(errors::PolymorphicConstantTooGeneric { span: constant.span });
                }
            }
            err
        })
    }

    /// This is a convenience helper for `simd_shuffle_indices`. It has the precondition
    /// that the given `constant` is an `ConstantKind::Unevaluated` and must be convertible to
    /// a `ValTree`. If you want a more general version of this, talk to `wg-const-eval` on zulip.
    pub fn eval_unevaluated_mir_constant_to_valtree(
        &self,
        constant: &mir::Constant<'tcx>,
    ) -> Result<Option<ty::ValTree<'tcx>>, ErrorHandled> {
        let uv = match self.monomorphize(constant.literal) {
            mir::ConstantKind::Unevaluated(uv, _) => uv.shrink(),
            mir::ConstantKind::Ty(c) => match c.kind() {
                // A constant that came from a const generic but was then used as an argument to old-style
                // simd_shuffle (passing as argument instead of as a generic param).
                rustc_type_ir::ConstKind::Value(valtree) => return Ok(Some(valtree)),
                other => span_bug!(constant.span, "{other:#?}"),
            },
            // We should never encounter `ConstantKind::Val` unless MIR opts (like const prop) evaluate
            // a constant and write that value back into `Operand`s. This could happen, but is unlikely.
            // Also: all users of `simd_shuffle` are on unstable and already need to take a lot of care
            // around intrinsics. For an issue to happen here, it would require a macro expanding to a
            // `simd_shuffle` call without wrapping the constant argument in a `const {}` block, but
            // the user pass through arbitrary expressions.
            // FIXME(oli-obk): replace the magic const generic argument of `simd_shuffle` with a real
            // const generic.
            other => span_bug!(constant.span, "{other:#?}"),
        };
        let uv = self.monomorphize(uv);
        self.cx.tcx().const_eval_resolve_for_typeck(
            ty::ParamEnv::reveal_all(),
            uv,
            Some(constant.span),
        )
    }

    /// process constant containing SIMD shuffle indices
    pub fn simd_shuffle_indices(
        &mut self,
        bx: &Bx,
        constant: &mir::Constant<'tcx>,
    ) -> (Bx::Value, Ty<'tcx>) {
        let ty = self.monomorphize(constant.ty());
        let val = self
            .eval_unevaluated_mir_constant_to_valtree(constant)
            .ok()
            .flatten()
            .map(|val| {
                let field_ty = ty.builtin_index().unwrap();
                let values: Vec<_> = val
                    .unwrap_branch()
                    .iter()
                    .map(|field| {
                        if let Some(prim) = field.try_to_scalar() {
                            let layout = bx.layout_of(field_ty);
                            let Abi::Scalar(scalar) = layout.abi else {
                                bug!("from_const: invalid ByVal layout: {:#?}", layout);
                            };
                            bx.scalar_to_backend(prim, scalar, bx.immediate_backend_type(layout))
                        } else {
                            bug!("simd shuffle field {:?}", field)
                        }
                    })
                    .collect();
                bx.const_struct(&values, false)
            })
            .unwrap_or_else(|| {
                bx.tcx().sess.emit_err(errors::ShuffleIndicesEvaluation { span: constant.span });
                // We've errored, so we don't have to produce working code.
                let llty = bx.backend_type(bx.layout_of(ty));
                bx.const_undef(llty)
            });
        (val, ty)
    }
}