LLVM 18 x86 data layout update

With https://reviews.llvm.org/D86310 LLVM now has i128 aligned to
16-bytes on x86 based platforms. This will be in LLVM-18. This patch
updates all our spec targets to be 16-byte aligned, and removes the
alignment when speaking to older LLVM.

This results in Rust overaligning things relative to LLVM on older LLVMs.

This alignment change was discussed in rust-lang/compiler-team#683

See #54341 for additional information about why this is happening and
where this will be useful in the future.

This *does not* stabilize `i128`/`u128` for FFI.

1 files changed, 6 insertions, 2 deletions

diff --git a/compiler/rustc_ast/src/ast.rs b/compiler/rustc_ast/src/ast.rs
index d0d98eb3d62..7f5213431f7 100644
--- a/compiler/rustc_ast/src/ast.rs
+++ b/compiler/rustc_ast/src/ast.rs
@@ -3304,9 +3304,13 @@ mod size_asserts {
     static_assert_size!(Impl, 136);
     static_assert_size!(Item, 136);
     static_assert_size!(ItemKind, 64);
-    static_assert_size!(LitKind, 24);
+    // This can be removed after i128:128 is in the bootstrap compiler's target.
+    #[cfg(not(bootstrap))]
+    static_assert_size!(LitKind, 32);
     static_assert_size!(Local, 72);
-    static_assert_size!(MetaItemLit, 40);
+    // This can be removed after i128:128 is in the bootstrap compiler's target.
+    #[cfg(not(bootstrap))]
+    static_assert_size!(MetaItemLit, 48);
     static_assert_size!(Param, 40);
     static_assert_size!(Pat, 72);
     static_assert_size!(Path, 24);