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.

4 files changed, 183 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]+.*}})
diff --git a/src/test/codegen/box-maybe-uninit.rs b/src/test/codegen/box-maybe-uninit.rs
index 5004f787cde..e105e26f16a 100644
--- a/src/test/codegen/box-maybe-uninit.rs
+++ b/src/test/codegen/box-maybe-uninit.rs
@@ -1,4 +1,5 @@
 // compile-flags: -O
+// min-llvm-version: 15.0
 #![crate_type="lib"]
 
 use std::mem::MaybeUninit;
@@ -16,3 +17,9 @@ pub fn box_uninitialized() -> Box<MaybeUninit<usize>> {
 
 // FIXME: add a test for a bigger box. Currently broken, see
 // https://github.com/rust-lang/rust/issues/58201.
+
+// Hide the `allocalign` attribute in the declaration of __rust_alloc
+// from the CHECK-NOT above, and also verify the attributes got set reasonably.
+// CHECK: declare noalias ptr @__rust_alloc(i{{[0-9]+}}, i{{[0-9]+}} allocalign) unnamed_addr [[RUST_ALLOC_ATTRS:#[0-9]+]]
+
+// CHECK-DAG: attributes [[RUST_ALLOC_ATTRS]] = { {{.*}} allockind("alloc,uninitialized,aligned") allocsize(0) uwtable "alloc-family"="__rust_alloc" {{.*}} }
diff --git a/src/test/codegen/vec-calloc-llvm14.rs b/src/test/codegen/vec-calloc-llvm14.rs
new file mode 100644
index 00000000000..08302796c41
--- /dev/null
+++ b/src/test/codegen/vec-calloc-llvm14.rs
@@ -0,0 +1,144 @@
+// compile-flags: -O
+// only-x86_64
+// ignore-debug
+
+#![crate_type = "lib"]
+
+// CHECK-LABEL: @vec_zero_bytes
+#[no_mangle]
+pub fn vec_zero_bytes(n: usize) -> Vec<u8> {
+    // CHECK-NOT: call {{.*}}alloc::vec::from_elem
+    // CHECK-NOT: call {{.*}}reserve
+    // CHECK-NOT: call {{.*}}__rust_alloc(
+    // CHECK-NOT: call {{.*}}llvm.memset
+
+    // CHECK: call {{.*}}__rust_alloc_zeroed(
+
+    // CHECK-NOT: call {{.*}}alloc::vec::from_elem
+    // CHECK-NOT: call {{.*}}reserve
+    // CHECK-NOT: call {{.*}}__rust_alloc(
+    // CHECK-NOT: call {{.*}}llvm.memset
+
+    // CHECK: ret void
+    vec![0; n]
+}
+
+// CHECK-LABEL: @vec_one_bytes
+#[no_mangle]
+pub fn vec_one_bytes(n: usize) -> Vec<u8> {
+    // CHECK-NOT: call {{.*}}alloc::vec::from_elem
+    // CHECK-NOT: call {{.*}}reserve
+    // CHECK-NOT: call {{.*}}__rust_alloc_zeroed(
+
+    // CHECK: call {{.*}}__rust_alloc(
+    // CHECK: call {{.*}}llvm.memset
+
+    // CHECK-NOT: call {{.*}}alloc::vec::from_elem
+    // CHECK-NOT: call {{.*}}reserve
+    // CHECK-NOT: call {{.*}}__rust_alloc_zeroed(
+
+    // CHECK: ret void
+    vec![1; n]
+}
+
+// CHECK-LABEL: @vec_zero_scalar
+#[no_mangle]
+pub fn vec_zero_scalar(n: usize) -> Vec<i32> {
+    // CHECK-NOT: call {{.*}}alloc::vec::from_elem
+    // CHECK-NOT: call {{.*}}reserve
+    // CHECK-NOT: call {{.*}}__rust_alloc(
+
+    // CHECK: call {{.*}}__rust_alloc_zeroed(
+
+    // CHECK-NOT: call {{.*}}alloc::vec::from_elem
+    // CHECK-NOT: call {{.*}}reserve
+    // CHECK-NOT: call {{.*}}__rust_alloc(
+
+    // CHECK: ret void
+    vec![0; n]
+}
+
+// CHECK-LABEL: @vec_one_scalar
+#[no_mangle]
+pub fn vec_one_scalar(n: usize) -> Vec<i32> {
+    // CHECK-NOT: call {{.*}}alloc::vec::from_elem
+    // CHECK-NOT: call {{.*}}reserve
+    // CHECK-NOT: call {{.*}}__rust_alloc_zeroed(
+
+    // CHECK: call {{.*}}__rust_alloc(
+
+    // CHECK-NOT: call {{.*}}alloc::vec::from_elem
+    // CHECK-NOT: call {{.*}}reserve
+    // CHECK-NOT: call {{.*}}__rust_alloc_zeroed(
+
+    // CHECK: ret void
+    vec![1; n]
+}
+
+// CHECK-LABEL: @vec_zero_rgb48
+#[no_mangle]
+pub fn vec_zero_rgb48(n: usize) -> Vec<[u16; 3]> {
+    // CHECK-NOT: call {{.*}}alloc::vec::from_elem
+    // CHECK-NOT: call {{.*}}reserve
+    // CHECK-NOT: call {{.*}}__rust_alloc(
+
+    // CHECK: call {{.*}}__rust_alloc_zeroed(
+
+    // CHECK-NOT: call {{.*}}alloc::vec::from_elem
+    // CHECK-NOT: call {{.*}}reserve
+    // CHECK-NOT: call {{.*}}__rust_alloc(
+
+    // CHECK: ret void
+    vec![[0, 0, 0]; n]
+}
+
+// CHECK-LABEL: @vec_zero_array_16
+#[no_mangle]
+pub fn vec_zero_array_16(n: usize) -> Vec<[i64; 16]> {
+    // CHECK-NOT: call {{.*}}alloc::vec::from_elem
+    // CHECK-NOT: call {{.*}}reserve
+    // CHECK-NOT: call {{.*}}__rust_alloc(
+
+    // CHECK: call {{.*}}__rust_alloc_zeroed(
+
+    // CHECK-NOT: call {{.*}}alloc::vec::from_elem
+    // CHECK-NOT: call {{.*}}reserve
+    // CHECK-NOT: call {{.*}}__rust_alloc(
+
+    // CHECK: ret void
+    vec![[0_i64; 16]; n]
+}
+
+// CHECK-LABEL: @vec_zero_tuple
+#[no_mangle]
+pub fn vec_zero_tuple(n: usize) -> Vec<(i16, u8, char)> {
+    // CHECK-NOT: call {{.*}}alloc::vec::from_elem
+    // CHECK-NOT: call {{.*}}reserve
+    // CHECK-NOT: call {{.*}}__rust_alloc(
+
+    // CHECK: call {{.*}}__rust_alloc_zeroed(
+
+    // CHECK-NOT: call {{.*}}alloc::vec::from_elem
+    // CHECK-NOT: call {{.*}}reserve
+    // CHECK-NOT: call {{.*}}__rust_alloc(
+
+    // CHECK: ret void
+    vec![(0, 0, '\0'); n]
+}
+
+// CHECK-LABEL: @vec_non_zero_tuple
+#[no_mangle]
+pub fn vec_non_zero_tuple(n: usize) -> Vec<(i16, u8, char)> {
+    // CHECK-NOT: call {{.*}}alloc::vec::from_elem
+    // CHECK-NOT: call {{.*}}reserve
+    // CHECK-NOT: call {{.*}}__rust_alloc_zeroed(
+
+    // CHECK: call {{.*}}__rust_alloc(
+
+    // CHECK-NOT: call {{.*}}alloc::vec::from_elem
+    // CHECK-NOT: call {{.*}}reserve
+    // CHECK-NOT: call {{.*}}__rust_alloc_zeroed(
+
+    // CHECK: ret void
+    vec![(0, 0, 'A'); n]
+}
diff --git a/src/test/codegen/vec-calloc.rs b/src/test/codegen/vec-calloc.rs
index 08302796c41..435a4ab5187 100644
--- a/src/test/codegen/vec-calloc.rs
+++ b/src/test/codegen/vec-calloc.rs
@@ -1,6 +1,7 @@
 // compile-flags: -O
 // only-x86_64
 // ignore-debug
+// min-llvm-version: 15.0
 
 #![crate_type = "lib"]
 
@@ -142,3 +143,8 @@ pub fn vec_non_zero_tuple(n: usize) -> Vec<(i16, u8, char)> {
     // CHECK: ret void
     vec![(0, 0, 'A'); n]
 }
+
+// Ensure that __rust_alloc_zeroed gets the right attributes for LLVM to optimize it away.
+// CHECK: declare noalias ptr @__rust_alloc_zeroed(i64, i64 allocalign) unnamed_addr [[RUST_ALLOC_ZEROED_ATTRS:#[0-9]+]]
+
+// CHECK-DAG: attributes [[RUST_ALLOC_ZEROED_ATTRS]] = { {{.*}} allockind("alloc,zeroed,aligned") allocsize(0) uwtable "alloc-family"="__rust_alloc" {{.*}} }