codegen: use new {re,de,}allocator annotations in llvm

This obviates the patch that teaches LLVM internals about
_rust_{re,de}alloc functions by putting annotations directly in the IR
for the optimizer.

The sole test change is required to anchor FileCheck to the body of the
`box_uninitialized` method, so it doesn't see the `allocalign` on
`__rust_alloc` and get mad about the string `alloca` showing up. Since I
was there anyway, I added some checks on the attributes to prove the
right attributes got set.

While we're here, we also emit allocator attributes on
__rust_alloc_zeroed. This should allow LLVM to perform more
optimizations for zeroed blocks, and probably fixes #90032. [This
comment](https://github.com/rust-lang/rust/issues/24194#issuecomment-308791157)
mentions "weird UB-like behaviour with bitvec iterators in
rustc_data_structures" so we may need to back this change out if things
go wrong.

The new test cases require LLVM 15, so we copy them into LLVM
14-supporting versions, which we can delete when we drop LLVM 14.

1 files changed, 26 insertions, 0 deletions

diff --git a/src/test/codegen/box-maybe-uninit-llvm14.rs b/src/test/codegen/box-maybe-uninit-llvm14.rs
new file mode 100644
index 00000000000..bd1a6599c33
--- /dev/null
+++ b/src/test/codegen/box-maybe-uninit-llvm14.rs
@@ -0,0 +1,26 @@
+// compile-flags: -O
+
+// Once we're done with llvm 14 and earlier, this test can be deleted.
+
+#![crate_type="lib"]
+
+use std::mem::MaybeUninit;
+
+// Boxing a `MaybeUninit` value should not copy junk from the stack
+#[no_mangle]
+pub fn box_uninitialized() -> Box<MaybeUninit<usize>> {
+    // CHECK-LABEL: @box_uninitialized
+    // CHECK-NOT: store
+    // CHECK-NOT: alloca
+    // CHECK-NOT: memcpy
+    // CHECK-NOT: memset
+    Box::new(MaybeUninit::uninit())
+}
+
+// FIXME: add a test for a bigger box. Currently broken, see
+// https://github.com/rust-lang/rust/issues/58201.
+
+// Hide the LLVM 15+ `allocalign` attribute in the declaration of __rust_alloc
+// from the CHECK-NOT above. We don't check the attributes here because we can't rely
+// on all of them being set until LLVM 15.
+// CHECK: declare noalias{{.*}} @__rust_alloc(i{{[0-9]+}}, i{{[0-9]+.*}})