Fix broken codegen for [expr; n] where "expr" diverges

src/librustc_trans/trans/tvec.rs

@@ -410,8 +410,12 @@ pub fn iter_vec_loop<'blk, 'tcx, F>(bcx: Block<'blk, 'tcx>,
     F: FnOnce(Block<'blk, 'tcx>, ValueRef, Ty<'tcx>) -> Block<'blk, 'tcx>,
 {
     let _icx = push_ctxt("tvec::iter_vec_loop");
-    let fcx = bcx.fcx;
 
+    if bcx.unreachable.get() {
+        return bcx;
+    }
+
+    let fcx = bcx.fcx;
     let loop_bcx = fcx.new_temp_block("expr_repeat");
     let next_bcx = fcx.new_temp_block("expr_repeat: next");
 

src/test/run-fail/issue-23354-2.rs

@@ -0,0 +1,17 @@
+// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// error-pattern:panic evaluated
+
+#[allow(unused_variables)]
+fn main() {
+    // This used to trigger an LLVM assertion during compilation
+    let x = [panic!("panic evaluated"); 2];
+}