Implement indexing for slices

Author: bjorn3

examples/example.rs

@@ -180,3 +180,7 @@ fn make_array() -> [u8; 3] {
 fn some_promoted_tuple() -> &'static (&'static str, &'static str) {
     &("abc", "some")
 }
+
+fn index_slice(s: &[u8]) -> u8 {
+    s[2]
+}

examples/mini_core.rs

@@ -207,3 +207,11 @@ impl<T> Index<usize> for [T; 3] {
         &self[index]
     }
 }
+
+impl<T> Index<usize> for [T] {
+    type Output = T;
+
+    fn index(&self, index: usize) -> &Self::Output {
+        &self[index]
+    }
+}

src/common.rs

@@ -433,21 +433,24 @@ impl<'a, 'tcx: 'a> CPlace<'tcx> {
         fx: &mut FunctionCx<'a, 'tcx, impl Backend>,
         index: Value,
     ) -> CPlace<'tcx> {
-        match self.layout().ty.sty {
-            ty::Array(elem_ty, _) => {
-                let elem_layout = fx.layout_of(elem_ty);
+        let (elem_layout, addr) = match self.layout().ty.sty {
+            ty::Array(elem_ty, _) => (fx.layout_of(elem_ty), self.expect_addr()),
+            ty::Slice(elem_ty) => (
+                fx.layout_of(elem_ty),
+                match self {
+                    CPlace::Addr(addr, _, _) => addr,
+                    CPlace::Var(_, _) => bug!("Expected CPlace::Addr found CPlace::Var"),
+                },
+            ),
+            _ => bug!("place_index({:?})", self.layout().ty),
+        };
 
-                let offset = fx
-                    .bcx
-                    .ins()
-                    .imul_imm(index, elem_layout.size.bytes() as i64);
+        let offset = fx
+            .bcx
+            .ins()
+            .imul_imm(index, elem_layout.size.bytes() as i64);
 
-                let addr = self.expect_addr();
-                CPlace::Addr(fx.bcx.ins().iadd(addr, offset), None, elem_layout)
-            }
-            ty::Slice(_elem_ty) => unimpl!("place_index(TySlice)"),
-            _ => bug!("place_index({:?})", self.layout().ty),
-        }
+        CPlace::Addr(fx.bcx.ins().iadd(addr, offset), None, elem_layout)
     }
 
     pub fn place_deref(self, fx: &mut FunctionCx<'a, 'tcx, impl Backend>) -> CPlace<'tcx> {