Auto merge of #52712 - oli-obk:const_eval_cleanups, r=RalfJung

Reintroduce `Undef` and properly check constant value sizes

r? @RalfJung

cc @eddyb

basically all kinds of silent failures that never occurred are assertions now

2 files changed, 17 insertions, 11 deletions

diff --git a/src/librustc_codegen_llvm/mir/constant.rs b/src/librustc_codegen_llvm/mir/constant.rs
index 341ed9df64b..267db4467c2 100644
--- a/src/librustc_codegen_llvm/mir/constant.rs
+++ b/src/librustc_codegen_llvm/mir/constant.rs
@@ -39,10 +39,12 @@ pub fn scalar_to_llvm(
 ) -> &'ll Value {
     let bitsize = if layout.is_bool() { 1 } else { layout.value.size(cx).bits() };
     match cv {
-        Scalar::Bits { defined, .. } if (defined as u64) < bitsize || defined == 0 => {
-            C_undef(Type::ix(cx, bitsize))
+        Scalar::Bits { size: 0, .. } => {
+            assert_eq!(0, layout.value.size(cx).bytes());
+            C_undef(Type::ix(cx, 0))
         },
-        Scalar::Bits { bits, .. } => {
+        Scalar::Bits { bits, size } => {
+            assert_eq!(size as u64, layout.value.size(cx).bytes());
             let llval = C_uint_big(Type::ix(cx, bitsize), bits);
             if layout.value == layout::Pointer {
                 unsafe { llvm::LLVMConstIntToPtr(llval, llty) }
@@ -192,7 +194,7 @@ impl FunctionCx<'a, 'll, 'tcx> {
                         mir::Field::new(field as usize),
                         c,
                     )?;
-                    if let Some(prim) = field.to_scalar() {
+                    if let Some(prim) = field.val.try_to_scalar() {
                         let layout = bx.cx.layout_of(field_ty);
                         let scalar = match layout.abi {
                             layout::Abi::Scalar(ref x) => x,
diff --git a/src/librustc_codegen_llvm/mir/operand.rs b/src/librustc_codegen_llvm/mir/operand.rs
index 1296f5e4b14..f8166ee6491 100644
--- a/src/librustc_codegen_llvm/mir/operand.rs
+++ b/src/librustc_codegen_llvm/mir/operand.rs
@@ -10,7 +10,7 @@
 
 use rustc::mir::interpret::ConstEvalErr;
 use rustc::mir;
-use rustc::mir::interpret::ConstValue;
+use rustc::mir::interpret::{ConstValue, ScalarMaybeUndef};
 use rustc::ty;
 use rustc::ty::layout::{self, Align, LayoutOf, TyLayout};
 use rustc_data_structures::indexed_vec::Idx;
@@ -110,12 +110,16 @@ impl OperandRef<'ll, 'tcx> {
                     a_scalar,
                     layout.scalar_pair_element_llvm_type(bx.cx, 0, true),
                 );
-                let b_llval = scalar_to_llvm(
-                    bx.cx,
-                    b,
-                    b_scalar,
-                    layout.scalar_pair_element_llvm_type(bx.cx, 1, true),
-                );
+                let b_layout = layout.scalar_pair_element_llvm_type(bx.cx, 1, true);
+                let b_llval = match b {
+                    ScalarMaybeUndef::Scalar(b) => scalar_to_llvm(
+                        bx.cx,
+                        b,
+                        b_scalar,
+                        b_layout,
+                    ),
+                    ScalarMaybeUndef::Undef => C_undef(b_layout),
+                };
                 OperandValue::Pair(a_llval, b_llval)
             },
             ConstValue::ByRef(alloc, offset) => {