1 files changed, 52 insertions, 0 deletions
diff --git a/compiler/rustc_mir_build/src/thir/constant.rs b/compiler/rustc_mir_build/src/thir/constant.rs
new file mode 100644
index 000000000..a7e4403a2
--- /dev/null
+++ b/compiler/rustc_mir_build/src/thir/constant.rs
@@ -0,0 +1,52 @@
+use rustc_ast as ast;
+use rustc_middle::mir::interpret::{LitToConstError, LitToConstInput};
+use rustc_middle::ty::{self, ParamEnv, ScalarInt, TyCtxt};
+
+pub(crate) fn lit_to_const<'tcx>(
+    tcx: TyCtxt<'tcx>,
+    lit_input: LitToConstInput<'tcx>,
+) -> Result<ty::Const<'tcx>, LitToConstError> {
+    let LitToConstInput { lit, ty, neg } = lit_input;
+
+    let trunc = |n| {
+        let param_ty = ParamEnv::reveal_all().and(ty);
+        let width = tcx.layout_of(param_ty).map_err(|_| LitToConstError::Reported)?.size;
+        trace!("trunc {} with size {} and shift {}", n, width.bits(), 128 - width.bits());
+        let result = width.truncate(n);
+        trace!("trunc result: {}", result);
+
+        Ok(ScalarInt::try_from_uint(result, width)
+            .unwrap_or_else(|| bug!("expected to create ScalarInt from uint {:?}", result)))
+    };
+
+    let valtree = match (lit, &ty.kind()) {
+        (ast::LitKind::Str(s, _), ty::Ref(_, inner_ty, _)) if inner_ty.is_str() => {
+            let str_bytes = s.as_str().as_bytes();
+            ty::ValTree::from_raw_bytes(tcx, str_bytes)
+        }
+        (ast::LitKind::ByteStr(data), ty::Ref(_, inner_ty, _))
+            if matches!(inner_ty.kind(), ty::Slice(_)) =>
+        {
+            let bytes = data as &[u8];
+            ty::ValTree::from_raw_bytes(tcx, bytes)
+        }
+        (ast::LitKind::ByteStr(data), ty::Ref(_, inner_ty, _)) if inner_ty.is_array() => {
+            let bytes = data as &[u8];
+            ty::ValTree::from_raw_bytes(tcx, bytes)
+        }
+        (ast::LitKind::Byte(n), ty::Uint(ty::UintTy::U8)) => {
+            ty::ValTree::from_scalar_int((*n).into())
+        }
+        (ast::LitKind::Int(n, _), ty::Uint(_)) | (ast::LitKind::Int(n, _), ty::Int(_)) => {
+            let scalar_int =
+                trunc(if neg { (*n as i128).overflowing_neg().0 as u128 } else { *n })?;
+            ty::ValTree::from_scalar_int(scalar_int)
+        }
+        (ast::LitKind::Bool(b), ty::Bool) => ty::ValTree::from_scalar_int((*b).into()),
+        (ast::LitKind::Char(c), ty::Char) => ty::ValTree::from_scalar_int((*c).into()),
+        (ast::LitKind::Err(_), _) => return Err(LitToConstError::Reported),
+        _ => return Err(LitToConstError::TypeError),
+    };
+
+    Ok(ty::Const::from_value(tcx, valtree, ty))
+}