rollup merge of #22437: dotdash/fix_array_type

In trans_slice_vec we currently use arrayalloca, which gives us a
pointer to the element type with enough memory allocated for the
requested number of elements.  This works, but everywhere else we use
the [n x T] type for fixed size arrays and so we have to bitcast the
pointer here. Let's directly use the proper type for the allocation and
remove some code duplication along the way.

Author: alexcrichton

src/librustc_trans/trans/base.rs

@@ -1219,19 +1219,6 @@ pub fn alloca_zeroed<'blk, 'tcx>(cx: Block<'blk, 'tcx>, ty: Ty<'tcx>,
     p
 }
 
-pub fn arrayalloca(cx: Block, ty: Type, v: ValueRef) -> ValueRef {
-    let _icx = push_ctxt("arrayalloca");
-    if cx.unreachable.get() {
-        unsafe {
-            return llvm::LLVMGetUndef(ty.to_ref());
-        }
-    }
-    debuginfo::clear_source_location(cx.fcx);
-    let p = ArrayAlloca(cx, ty, v);
-    call_lifetime_start(cx, p);
-    p
-}
-
 // Creates the alloca slot which holds the pointer to the slot for the final return value
 pub fn make_return_slot_pointer<'a, 'tcx>(fcx: &FunctionContext<'a, 'tcx>,
                                           output_type: Ty<'tcx>) -> ValueRef {

src/librustc_trans/trans/tvec.rs

@@ -171,33 +171,27 @@ pub fn trans_slice_vec<'blk, 'tcx>(bcx: Block<'blk, 'tcx>,
     let vt = vec_types_from_expr(bcx, content_expr);
     let count = elements_required(bcx, content_expr);
     debug!("    vt={}, count={}", vt.to_string(ccx), count);
-    let llcount = C_uint(ccx, count);
 
     let fixed_ty = ty::mk_vec(bcx.tcx(),
                               vt.unit_ty,
                               Some(count));
-    let llfixed_ty = type_of::type_of(bcx.ccx(), fixed_ty).ptr_to();
+    let llfixed_ty = type_of::type_of(bcx.ccx(), fixed_ty);
 
-    let llfixed = if count == 0 {
-        // Just create a zero-sized alloca to preserve
-        // the non-null invariant of the inner slice ptr
-        let llfixed = base::arrayalloca(bcx, vt.llunit_ty, llcount);
-        BitCast(bcx, llfixed, llfixed_ty)
-    } else {
-        // Make a fixed-length backing array and allocate it on the stack.
-        let llfixed = base::arrayalloca(bcx, vt.llunit_ty, llcount);
+    // Always create an alloca even if zero-sized, to preserve
+    // the non-null invariant of the inner slice ptr
+    let llfixed = base::alloca(bcx, llfixed_ty, "");
 
+    if count > 0 {
         // Arrange for the backing array to be cleaned up.
-        let llfixed_casted = BitCast(bcx, llfixed, llfixed_ty);
         let cleanup_scope = cleanup::temporary_scope(bcx.tcx(), content_expr.id);
-        fcx.schedule_lifetime_end(cleanup_scope, llfixed_casted);
-        fcx.schedule_drop_mem(cleanup_scope, llfixed_casted, fixed_ty);
+        fcx.schedule_lifetime_end(cleanup_scope, llfixed);
+        fcx.schedule_drop_mem(cleanup_scope, llfixed, fixed_ty);
 
         // Generate the content into the backing array.
-        bcx = write_content(bcx, &vt, slice_expr,
-                            content_expr, SaveIn(llfixed));
-
-        llfixed_casted
+        // llfixed has type *[T x N], but we want the type *T,
+        // so use GEP to convert
+        bcx = write_content(bcx, &vt, slice_expr, content_expr,
+                            SaveIn(GEPi(bcx, llfixed, &[0, 0])));
     };
 
     immediate_rvalue_bcx(bcx, llfixed, vec_ty).to_expr_datumblock()