u128 truncation and sign extension are not just interpreter related

compiler/rustc_symbol_mangling/src/v0.rs

@@ -4,7 +4,6 @@ use rustc_data_structures::fx::{FxHashMap, FxHashSet};
 use rustc_hir as hir;
 use rustc_hir::def_id::{CrateNum, DefId};
 use rustc_hir::definitions::{DefPathData, DisambiguatedDefPathData};
-use rustc_middle::mir::interpret::sign_extend;
 use rustc_middle::ty::print::{Print, Printer};
 use rustc_middle::ty::subst::{GenericArg, GenericArgKind, Subst};
 use rustc_middle::ty::{self, Instance, Ty, TyCtxt, TypeFoldable};
@@ -527,7 +526,7 @@ impl Printer<'tcx> for SymbolMangler<'tcx> {
                 let param_env = ty::ParamEnv::reveal_all();
                 ct.try_eval_bits(self.tcx, param_env, ct.ty).and_then(|b| {
                     let sz = self.tcx.layout_of(param_env.and(ct.ty)).ok()?.size;
-                    let val = sign_extend(b, sz) as i128;
+                    let val = sz.sign_extend(b) as i128;
                     if val < 0 {
                         neg = true;
                     }