Add fallible Scalar to ScalarInt conversion method

Author: oli-obk

compiler/rustc_middle/src/mir/interpret/value.rs

@@ -346,16 +346,13 @@ impl<'tcx, Tag> Scalar<Tag> {
     #[inline]
     fn to_bits(self, target_size: Size) -> InterpResult<'tcx, u128> {
         assert_ne!(target_size.bytes(), 0, "you should never look at the bits of a ZST");
-        match self {
-            Scalar::Int(int) => int.to_bits(target_size).map_err(|size| {
-                err_ub!(ScalarSizeMismatch {
-                    target_size: target_size.bytes(),
-                    data_size: size.bytes(),
-                })
-                .into()
-            }),
-            Scalar::Ptr(_) => throw_unsup!(ReadPointerAsBytes),
-        }
+        self.to_int()?.to_bits(target_size).map_err(|size| {
+            err_ub!(ScalarSizeMismatch {
+                target_size: target_size.bytes(),
+                data_size: size.bytes(),
+            })
+            .into()
+        })
     }
 
     #[inline(always)]
@@ -364,13 +361,18 @@ impl<'tcx, Tag> Scalar<Tag> {
     }
 
     #[inline]
-    pub fn assert_int(self) -> ScalarInt {
+    pub fn to_int(self) -> InterpResult<'tcx, ScalarInt> {
         match self {
-            Scalar::Ptr(_) => bug!("expected an int but got an abstract pointer"),
-            Scalar::Int(int) => int,
+            Scalar::Ptr(_) => throw_unsup!(ReadPointerAsBytes),
+            Scalar::Int(int) => Ok(int),
         }
     }
 
+    #[inline]
+    pub fn assert_int(self) -> ScalarInt {
+        self.to_int().expect("expected an int but got an abstract pointer")
+    }
+
     #[inline]
     pub fn assert_ptr(self) -> Pointer<Tag> {
         match self {