Rollup merge of rust-lang#140460 - heiher:issue-140455, r=Urgau

Fix handling of LoongArch target features not supported by LLVM 19

Fixes rust-lang#140455

Author: Zalathar

compiler/rustc_codegen_llvm/src/llvm_util.rs

@@ -273,6 +273,12 @@ pub(crate) fn to_llvm_features<'a>(sess: &Session, s: &'a str) -> Option<LLVMFea
         ("aarch64", "fpmr") => None, // only existed in 18
         ("arm", "fp16") => Some(LLVMFeature::new("fullfp16")),
         // Filter out features that are not supported by the current LLVM version
+        ("loongarch64", "div32" | "lam-bh" | "lamcas" | "ld-seq-sa" | "scq")
+            if get_version().0 < 20 =>
+        {
+            None
+        }
+        // Filter out features that are not supported by the current LLVM version
         ("riscv32" | "riscv64", "zacas") if get_version().0 < 20 => None,
         // Enable the evex512 target feature if an avx512 target feature is enabled.
         ("x86", s) if s.starts_with("avx512") => {

compiler/rustc_target/src/target_features.rs

@@ -102,6 +102,9 @@ impl Stability {
 // check whether they're named already elsewhere in rust
 // e.g. in stdarch and whether the given name matches LLVM's
 // if it doesn't, to_llvm_feature in llvm_util in rustc_codegen_llvm needs to be adapted.
+// Additionally, if the feature is not available in older version of LLVM supported by the current
+// rust, the same function must be updated to filter out these features to avoid triggering
+// warnings.
 //
 // Also note that all target features listed here must be purely additive: for target_feature 1.1 to
 // be sound, we can never allow features like `+soft-float` (on x86) to be controlled on a