Adjust 64-bit ARM data layouts for LLVM update

LLVM has updated data layouts to specify `Fn32` on 64-bit ARM to avoid
C++ accidentally underaligning functions when trying to comply with
member function ABIs.

This should only affect Rust in cases where we had a similar bug (I
don't believe we have one), but our data layout must match to generate
code.

As a compatibility adaptatation, if LLVM is not version 19 yet, `Fn32`
gets voided from the data layout.

See llvm/llvm-project#90415

1 files changed, 9 insertions, 0 deletions

diff --git a/compiler/rustc_codegen_llvm/src/context.rs b/compiler/rustc_codegen_llvm/src/context.rs
index 653abb4e41b..53a098d178e 100644
--- a/compiler/rustc_codegen_llvm/src/context.rs
+++ b/compiler/rustc_codegen_llvm/src/context.rs
@@ -133,6 +133,15 @@ pub unsafe fn create_module<'ll>(
         }
     }
 
+    if llvm_version < (19, 0, 0) {
+        if sess.target.arch == "aarch64" || sess.target.arch.starts_with("arm64") {
+            // LLVM 19 sets -Fn32 in its data layout string for 64-bit ARM
+            // Earlier LLVMs leave this default, so remove it.
+            // See https://github.com/llvm/llvm-project/pull/90702
+            target_data_layout = target_data_layout.replace("-Fn32", "");
+        }
+    }
+
     // Ensure the data-layout values hardcoded remain the defaults.
     {
         let tm = crate::back::write::create_informational_target_machine(tcx.sess);