Disable f16 on Aarch64 without neon for llvm < 20.1.1

This check was added unconditionally in c51b229140 ("Disable f16 on
Aarch64 without `neon`") and reverted in 4a8d35709e ("Revert "Disable
`f16` on Aarch64 without `neon`"") since it did not fail in Rust's
build. However, it is still possible to hit this crash if using LLVM 19
built with assertions, so disable the type conditionally based on
version here.

Note that for these builds, a similar patch is needed in the build
script for `compiler-builtins` since it does not yet use
`cfg(target_has_reliable_f16)` (hopefully to be resolved in the near
future).

Report: https://www.github.com/rust-lang/rust/pull/139276#issuecomment-3014781652
Original LLVM issue: https://www.github.com/llvm/llvm-project/issues/129394

1 files changed, 8 insertions, 0 deletions

diff --git a/compiler/rustc_codegen_llvm/src/llvm_util.rs b/compiler/rustc_codegen_llvm/src/llvm_util.rs
index 6fd07d562af..0fb987bdf82 100644
--- a/compiler/rustc_codegen_llvm/src/llvm_util.rs
+++ b/compiler/rustc_codegen_llvm/src/llvm_util.rs
@@ -370,10 +370,18 @@ fn update_target_reliable_float_cfg(sess: &Session, cfg: &mut TargetConfig) {
     let target_env = sess.target.options.env.as_ref();
     let target_abi = sess.target.options.abi.as_ref();
     let target_pointer_width = sess.target.pointer_width;
+    let version = get_version();
 
     cfg.has_reliable_f16 = match (target_arch, target_os) {
         // Selection failure <https://github.com/llvm/llvm-project/issues/50374>
         ("s390x", _) => false,
+        // LLVM crash without neon <https://github.com/llvm/llvm-project/issues/129394> (now fixed)
+        ("aarch64", _)
+            if !cfg.target_features.iter().any(|f| f.as_str() == "neon")
+                && version < (20, 1, 1) =>
+        {
+            false
+        }
         // Unsupported <https://github.com/llvm/llvm-project/issues/94434>
         ("arm64ec", _) => false,
         // MinGW ABI bugs <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115054>