From efd203aa0b7d748bcf5a76efe810f025306fd901 Mon Sep 17 00:00:00 2001
From: bjorn3 <bjorn3@users.noreply.github.com>
Date: Wed, 8 Aug 2018 12:22:16 +0200
Subject: [PATCH] Implement indexing for arrays

---
 examples/example.rs   |  4 ++++
 examples/mini_core.rs | 14 ++++++++++++++
 src/base.rs           |  3 ++-
 src/common.rs         | 15 +++++++++++++++
 4 files changed, 35 insertions(+), 1 deletion(-)

diff --git a/examples/example.rs b/examples/example.rs
index 0537db405d3e..74735c6a12de 100644
--- a/examples/example.rs
+++ b/examples/example.rs
@@ -142,3 +142,7 @@ unsafe fn call_uninit() -> u8 {
 /*unsafe fn deref_str_ptr(s: *const str) -> &'static str {
     &*s
 }*/
+
+fn use_array(arr: [u8; 3]) -> u8 {
+    arr[1]
+}
diff --git a/examples/mini_core.rs b/examples/mini_core.rs
index ff22aad5a65d..dc19d66b2144 100644
--- a/examples/mini_core.rs
+++ b/examples/mini_core.rs
@@ -141,3 +141,17 @@ pub mod intrinsics {
         pub fn uninit<T>() -> T;
     }
 }
+
+#[lang = "index"]
+pub trait Index<Idx: ?Sized> {
+    type Output: ?Sized;
+    fn index(&self, index: Idx) -> &Self::Output;
+}
+
+impl<T> Index<usize> for [T; 3] {
+    type Output = T;
+
+    fn index(&self, index: usize) -> &Self::Output {
+        &self[index]
+    }
+}
diff --git a/src/base.rs b/src/base.rs
index e0c4b80afcc4..723eb8cdc766 100644
--- a/src/base.rs
+++ b/src/base.rs
@@ -800,7 +800,8 @@ pub fn trans_place<'a, 'tcx: 'a>(
                 ),
                 ProjectionElem::Field(field, _ty) => base.place_field(fx, field),
                 ProjectionElem::Index(local) => {
-                    unimplemented!("projection index {:?} {:?}", projection.base, local)
+                    let index = fx.get_local_place(local).to_cvalue(fx).load_value(fx);
+                    base.place_index(fx, index)
                 }
                 ProjectionElem::ConstantIndex {
                     offset,
diff --git a/src/common.rs b/src/common.rs
index f49827b3a977..c3398a9e9f39 100644
--- a/src/common.rs
+++ b/src/common.rs
@@ -297,6 +297,21 @@ impl<'a, 'tcx: 'a> CPlace<'tcx> {
         CPlace::Addr(field_ptr, field_layout)
     }
 
+    pub fn place_index(self, fx: &mut FunctionCx<'a, 'tcx>, index: Value) -> CPlace<'tcx> {
+        let addr = self.expect_addr();
+        let layout = self.layout();
+        match layout.ty.sty {
+            TypeVariants::TyArray(elem_ty, _) => {
+                let elem_layout = fx.layout_of(elem_ty);
+                let size = fx.bcx.ins().iconst(types::I64, elem_layout.size.bytes() as i64);
+                let offset = fx.bcx.ins().imul(size, index);
+                CPlace::Addr(fx.bcx.ins().iadd(addr, offset), elem_layout)
+            }
+            TypeVariants::TySlice(_elem_ty) => unimplemented!("place_index(TySlice)"),
+            _ => bug!("place_index({:?})", layout.ty),
+        }
+    }
+
     pub fn unchecked_cast_to(self, layout: TyLayout<'tcx>) -> Self {
         match self {
             CPlace::Var(var, _) => CPlace::Var(var, layout),