src/librustc_codegen_ssa/mir/constant.rs

   1 use crate::mir::operand::OperandRef;
   2 use crate::traits::*;
   3 use rustc::mir;
   4 use rustc::mir::interpret::ErrorHandled;
   5 use rustc::ty::layout::{self, HasTyCtxt};
   6 use rustc::ty::{self, Ty};
   7 use rustc_index::vec::Idx;
   8 use rustc_span::source_map::Span;
   9
  10 use super::FunctionCx;
  11
  12 impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
  13     pub fn eval_mir_constant_to_operand(
  14         &mut self,
  15         bx: &mut Bx,
  16         constant: &mir::Constant<'tcx>,
  17     ) -> Result<OperandRef<'tcx, Bx::Value>, ErrorHandled> {
  18         match constant.literal.val {
  19             // Special case unevaluated statics, because statics have an identity and thus should
  20             // use `get_static` to get at their id.
  21             // FIXME(oli-obk): can we unify this somehow, maybe by making const eval of statics
  22             // always produce `&STATIC`. This may also simplify how const eval works with statics.
  23             ty::ConstKind::Unevaluated(def_id, substs, None) if self.cx.tcx().is_static(def_id) => {
  24                 assert!(substs.is_empty(), "we don't support generic statics yet");
  25                 let static_ = bx.get_static(def_id);
  26                 // we treat operands referring to statics as if they were `&STATIC` instead
  27                 let ptr_ty = self.cx.tcx().mk_mut_ptr(self.monomorphize(&constant.literal.ty));
  28                 let layout = bx.layout_of(ptr_ty);
  29                 Ok(OperandRef::from_immediate_or_packed_pair(bx, static_, layout))
  30             }
  31             _ => {
  32                 let val = self.eval_mir_constant(constant)?;
  33                 Ok(OperandRef::from_const(bx, val))
  34             }
  35         }
  36     }
  37
  38     pub fn eval_mir_constant(
  39         &mut self,
  40         constant: &mir::Constant<'tcx>,
  41     ) -> Result<&'tcx ty::Const<'tcx>, ErrorHandled> {
  42         match constant.literal.val {
  43             ty::ConstKind::Unevaluated(def_id, substs, promoted) => {
  44                 let substs = self.monomorphize(&substs);
  45                 self.cx
  46                     .tcx()
  47                     .const_eval_resolve(ty::ParamEnv::reveal_all(), def_id, substs, promoted, None)
  48                     .map_err(|err| {
  49                         if promoted.is_none() {
  50                             self.cx
  51                                 .tcx()
  52                                 .sess
  53                                 .span_err(constant.span, "erroneous constant encountered");
  54                         }
  55                         err
  56                     })
  57             }
  58             _ => Ok(self.monomorphize(&constant.literal)),
  59         }
  60     }
  61
  62     /// process constant containing SIMD shuffle indices
  63     pub fn simd_shuffle_indices(
  64         &mut self,
  65         bx: &Bx,
  66         span: Span,
  67         ty: Ty<'tcx>,
  68         constant: Result<&'tcx ty::Const<'tcx>, ErrorHandled>,
  69     ) -> (Bx::Value, Ty<'tcx>) {
  70         constant
  71             .map(|c| {
  72                 let field_ty = c.ty.builtin_index().unwrap();
  73                 let fields = match c.ty.kind {
  74                     ty::Array(_, n) => n.eval_usize(bx.tcx(), ty::ParamEnv::reveal_all()),
  75                     _ => bug!("invalid simd shuffle type: {}", c.ty),
  76                 };
  77                 let values: Vec<_> = (0..fields)
  78                     .map(|field| {
  79                         let field = bx.tcx().const_field(
  80                             ty::ParamEnv::reveal_all().and((&c, mir::Field::new(field as usize))),
  81                         );
  82                         if let Some(prim) = field.val.try_to_scalar() {
  83                             let layout = bx.layout_of(field_ty);
  84                             let scalar = match layout.abi {
  85                                 layout::Abi::Scalar(ref x) => x,
  86                                 _ => bug!("from_const: invalid ByVal layout: {:#?}", layout),
  87                             };
  88                             bx.scalar_to_backend(prim, scalar, bx.immediate_backend_type(layout))
  89                         } else {
  90                             bug!("simd shuffle field {:?}", field)
  91                         }
  92                     })
  93                     .collect();
  94                 let llval = bx.const_struct(&values, false);
  95                 (llval, c.ty)
  96             })
  97             .unwrap_or_else(|_| {
  98                 bx.tcx().sess.span_err(span, "could not evaluate shuffle_indices at compile time");
  99                 // We've errored, so we don't have to produce working code.
 100                 let ty = self.monomorphize(&ty);
 101                 let llty = bx.backend_type(bx.layout_of(ty));
 102                 (bx.const_undef(llty), ty)
 103             })
 104     }
 105 }