Stop turning transmutes into discriminants in mir-opt

Partially reverts 109612, as after 109993 these aren't actually equivalent any more, and I'm no longer confident this was ever an improvement in the first place.

1 files changed, 0 insertions, 13 deletions

diff --git a/compiler/rustc_mir_transform/src/instsimplify.rs b/compiler/rustc_mir_transform/src/instsimplify.rs
index 6bff535586a..e4dc617620e 100644
--- a/compiler/rustc_mir_transform/src/instsimplify.rs
+++ b/compiler/rustc_mir_transform/src/instsimplify.rs
@@ -5,7 +5,6 @@ use crate::MirPass;
 use rustc_hir::Mutability;
 use rustc_middle::mir::*;
 use rustc_middle::ty::layout::ValidityRequirement;
-use rustc_middle::ty::util::IntTypeExt;
 use rustc_middle::ty::{self, ParamEnv, SubstsRef, Ty, TyCtxt};
 use rustc_span::symbol::Symbol;
 use rustc_target::abi::FieldIdx;
@@ -163,18 +162,6 @@ impl<'tcx> InstSimplifyContext<'tcx, '_> {
                     return;
                 }
 
-                // Transmuting a fieldless enum to its repr is a discriminant read
-                if let ty::Adt(adt_def, ..) = operand_ty.kind()
-                    && adt_def.is_enum()
-                    && adt_def.is_payloadfree()
-                    && let Some(place) = operand.place()
-                    && let Some(repr_int) = adt_def.repr().int
-                    && repr_int.to_ty(self.tcx) == *cast_ty
-                {
-                    *rvalue = Rvalue::Discriminant(place);
-                    return;
-                }
-
                 // Transmuting a transparent struct/union to a field's type is a projection
                 if let ty::Adt(adt_def, substs) = operand_ty.kind()
                     && adt_def.repr().transparent()