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Explain the arguments of the mk_*_eval_cx functions

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This commit is contained in:
Oliver Scherer 2019-01-09 16:27:33 +01:00
parent f174b73caf
commit cd5a9e04da
1 changed files with 13 additions and 0 deletions
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13
src/librustc_mir/const_eval.rs
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@ -37,6 +37,14 @@ const DETECTOR_SNAPSHOT_PERIOD: isize = 256;
/// Warning: do not use this function if you expect to start interpreting the given `Mir`.
/// The `EvalContext` is only meant to be used to query values from constants and statics.
///
/// This function is used during const propagation. We cannot use `mk_eval_cx`, because copy
/// propagation happens *during* the computation of the MIR of the current function. So if we
/// tried to call the `optimized_mir` query, we'd get a cycle error because we are (transitively)
/// inside the `optimized_mir` query of the `Instance` given.
///
/// Since we are looking at the MIR of the function in an abstract manner, we don't have a
/// `ParamEnv` available to us. This function creates a `ParamEnv` for the given instance.
pub fn mk_borrowck_eval_cx<'a, 'mir, 'tcx>(
tcx: TyCtxt<'a, 'tcx, 'tcx>,
instance: Instance<'tcx>,
@ -78,6 +86,11 @@ fn mk_eval_cx_inner<'a, 'mir, 'tcx>(
/// Warning: do not use this function if you expect to start interpreting the given `Mir`.
/// The `EvalContext` is only meant to be used to do field and index projections into constants for
/// `simd_shuffle` and const patterns in match arms.
///
/// The function containing the `match` that is currently being analyzed may have generic bounds
/// that inform us about the generic bounds of the constant. E.g. using an associated constant
/// of a function's generic parameter will require knowledge about the bounds on the generic
/// parameter.
fn mk_eval_cx<'a, 'tcx>(
tcx: TyCtxt<'a, 'tcx, 'tcx>,
instance: Instance<'tcx>,