Rollup merge of #41361 - arielb1:move-mir-init, r=pnkfelix

lower `move_val_init` during MIR construction

Because of its "magic" order-of-evaluation semantics, `move_val_init` must be lowered during MIR construction in order to work without needing a temporary.

r? @eddyb

1 files changed, 29 insertions, 0 deletions

diff --git a/src/test/codegen/move-val-init.rs b/src/test/codegen/move-val-init.rs
new file mode 100644
index 00000000000..98b7db60b68
--- /dev/null
+++ b/src/test/codegen/move-val-init.rs
@@ -0,0 +1,29 @@
+// Copyright 2017 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.
+
+// compile-flags: -C no-prepopulate-passes
+
+#![feature(core_intrinsics)]
+#![crate_type = "lib"]
+
+// test that `move_val_init` actually avoids big allocas
+
+use std::intrinsics::move_val_init;
+
+pub struct Big {
+    pub data: [u8; 65536]
+}
+
+// CHECK-LABEL: @test_mvi
+#[no_mangle]
+pub unsafe fn test_mvi(target: *mut Big, make_big: fn() -> Big) {
+    // CHECK: call void %1(%Big*{{[^%]*}} %0)
+    move_val_init(target, make_big());
+}