diff options
| -rw-r--r-- | src/librustc_mir/const_eval.rs | 13 |
1 files changed, 13 insertions, 0 deletions
diff --git a/src/librustc_mir/const_eval.rs b/src/librustc_mir/const_eval.rs index 9b62743e9c6..594496fe972 100644 --- a/src/librustc_mir/const_eval.rs +++ b/src/librustc_mir/const_eval.rs @@ -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>, |