implement valtrees as the type-system representation for constant values

compiler/rustc_mir_build/src/build/expr/as_constant.rs

@@ -1,12 +1,16 @@
 //! See docs in build/expr/mod.rs
 
-use crate::build::{lit_to_mir_constant, Builder};
+use crate::build::{parse_float_into_constval, Builder};
+use rustc_ast as ast;
 use rustc_hir::def_id::DefId;
-use rustc_middle::mir::interpret::{ConstValue, LitToConstError, LitToConstInput, Scalar};
+use rustc_middle::mir::interpret::{
+    Allocation, ConstValue, LitToConstError, LitToConstInput, Scalar,
+};
 use rustc_middle::mir::*;
 use rustc_middle::thir::*;
 use rustc_middle::ty::subst::SubstsRef;
 use rustc_middle::ty::{self, CanonicalUserTypeAnnotation, Ty, TyCtxt};
+use rustc_target::abi::Size;
 
 impl<'a, 'tcx> Builder<'a, 'tcx> {
     /// Compile `expr`, yielding a compile-time constant. Assumes that
@@ -84,3 +88,54 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         }
     }
 }
+
+#[instrument(skip(tcx, lit_input))]
+pub(crate) fn lit_to_mir_constant<'tcx>(
+    tcx: TyCtxt<'tcx>,
+    lit_input: LitToConstInput<'tcx>,
+) -> Result<ConstantKind<'tcx>, LitToConstError> {
+    let LitToConstInput { lit, ty, neg } = lit_input;
+    let trunc = |n| {
+        let param_ty = 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(ConstValue::Scalar(Scalar::from_uint(result, width)))
+    };
+
+    let value = match (lit, &ty.kind()) {
+        (ast::LitKind::Str(s, _), ty::Ref(_, inner_ty, _)) if inner_ty.is_str() => {
+            let s = s.as_str();
+            let allocation = Allocation::from_bytes_byte_aligned_immutable(s.as_bytes());
+            let allocation = tcx.intern_const_alloc(allocation);
+            ConstValue::Slice { data: allocation, start: 0, end: s.len() }
+        }
+        (ast::LitKind::ByteStr(data), ty::Ref(_, inner_ty, _))
+            if matches!(inner_ty.kind(), ty::Slice(_)) =>
+        {
+            let allocation = Allocation::from_bytes_byte_aligned_immutable(data as &[u8]);
+            let allocation = tcx.intern_const_alloc(allocation);
+            ConstValue::Slice { data: allocation, start: 0, end: data.len() }
+        }
+        (ast::LitKind::ByteStr(data), ty::Ref(_, inner_ty, _)) if inner_ty.is_array() => {
+            let id = tcx.allocate_bytes(data);
+            ConstValue::Scalar(Scalar::from_pointer(id.into(), &tcx))
+        }
+        (ast::LitKind::Byte(n), ty::Uint(ty::UintTy::U8)) => {
+            ConstValue::Scalar(Scalar::from_uint(*n, Size::from_bytes(1)))
+        }
+        (ast::LitKind::Int(n, _), ty::Uint(_)) | (ast::LitKind::Int(n, _), ty::Int(_)) => {
+            trunc(if neg { (*n as i128).overflowing_neg().0 as u128 } else { *n })?
+        }
+        (ast::LitKind::Float(n, _), ty::Float(fty)) => {
+            parse_float_into_constval(*n, *fty, neg).ok_or(LitToConstError::Reported)?
+        }
+        (ast::LitKind::Bool(b), ty::Bool) => ConstValue::Scalar(Scalar::from_bool(*b)),
+        (ast::LitKind::Char(c), ty::Char) => ConstValue::Scalar(Scalar::from_char(*c)),
+        (ast::LitKind::Err(_), _) => return Err(LitToConstError::Reported),
+        _ => return Err(LitToConstError::TypeError),
+    };
+
+    Ok(ConstantKind::Val(value, ty))
+}