rustc_codegen_llvm: Reorder conversion cases

For maintainability, this commit reorders target feature conversion
cases into four categories:

1.  Non-default, relatively simple conversion (renames w/wo dependencies),
2.  Simple filtering to ignore unsupported LLVM features,
3.  Relatively complex conversion and
4.  The default case.

For each category, clauses are sorted by the architecture.

Author: a4lg

compiler/rustc_codegen_llvm/src/llvm_util.rs

@@ -226,15 +226,9 @@ pub(crate) fn to_llvm_features<'a>(sess: &Session, s: &'a str) -> Option<LLVMFea
         _ => raw_arch,
     };
     match (arch, s) {
-        ("x86", "sse4.2") => Some(LLVMFeature::with_dependencies(
-            "sse4.2",
-            smallvec![TargetFeatureFoldStrength::EnableOnly("crc32")],
-        )),
-        ("x86", "pclmulqdq") => Some(LLVMFeature::new("pclmul")),
-        ("x86", "rdrand") => Some(LLVMFeature::new("rdrnd")),
-        ("x86", "bmi1") => Some(LLVMFeature::new("bmi")),
-        ("x86", "cmpxchg16b") => Some(LLVMFeature::new("cx16")),
-        ("x86", "lahfsahf") => Some(LLVMFeature::new("sahf")),
+        /*
+            Perform relatively simple feature conversion cases.
+        */
         ("aarch64", "rcpc2") => Some(LLVMFeature::new("rcpc-immo")),
         ("aarch64", "dpb") => Some(LLVMFeature::new("ccpp")),
         ("aarch64", "dpb2") => Some(LLVMFeature::new("ccdp")),
@@ -243,10 +237,6 @@ pub(crate) fn to_llvm_features<'a>(sess: &Session, s: &'a str) -> Option<LLVMFea
         ("aarch64", "pmuv3") => Some(LLVMFeature::new("perfmon")),
         ("aarch64", "paca") => Some(LLVMFeature::new("pauth")),
         ("aarch64", "pacg") => Some(LLVMFeature::new("pauth")),
-        // Before LLVM 20 those two features were packaged together as b16b16
-        ("aarch64", "sve-b16b16" | "sme-b16b16") if get_version().0 < 20 => {
-            Some(LLVMFeature::new("b16b16"))
-        }
         ("aarch64", "flagm2") => Some(LLVMFeature::new("altnzcv")),
         // Rust ties fp and neon together.
         ("aarch64", "neon") => Some(LLVMFeature::with_dependencies(
@@ -257,22 +247,45 @@ pub(crate) fn to_llvm_features<'a>(sess: &Session, s: &'a str) -> Option<LLVMFea
         // neon when a feature only implicitly enables fp
         ("aarch64", "fhm") => Some(LLVMFeature::new("fp16fml")),
         ("aarch64", "fp16") => Some(LLVMFeature::new("fullfp16")),
-        // Filter out features that are not supported by the current LLVM version
-        ("aarch64", "fpmr") => None, // only existed in 18
         ("arm", "fp16") => Some(LLVMFeature::new("fullfp16")),
-        // NVPTX targets added in LLVM 20
-        (
-            "nvptx64",
-            "sm_100" | "sm_100a" | "sm_101" | "sm_101a" | "sm_120" | "sm_120a" | "ptx86" | "ptx87",
-        ) if get_version().0 < 20 => None,
-        // Filter out features that are not supported by the current LLVM version
+        ("powerpc", "power8-crypto") => Some(LLVMFeature::new("crypto")),
+        ("sparc", "leoncasa") => Some(LLVMFeature::new("hasleoncasa")),
+        ("x86", "sse4.2") => Some(LLVMFeature::with_dependencies(
+            "sse4.2",
+            smallvec![TargetFeatureFoldStrength::EnableOnly("crc32")],
+        )),
+        ("x86", "pclmulqdq") => Some(LLVMFeature::new("pclmul")),
+        ("x86", "rdrand") => Some(LLVMFeature::new("rdrnd")),
+        ("x86", "bmi1") => Some(LLVMFeature::new("bmi")),
+        ("x86", "cmpxchg16b") => Some(LLVMFeature::new("cx16")),
+        ("x86", "lahfsahf") => Some(LLVMFeature::new("sahf")),
+        ("x86", "avx10.1") => Some(LLVMFeature::new("avx10.1-512")),
+        ("x86", "apxf") => Some(LLVMFeature::with_dependencies(
+            "egpr",
+            smallvec![
+                TargetFeatureFoldStrength::Both("push2pop2"),
+                TargetFeatureFoldStrength::Both("ppx"),
+                TargetFeatureFoldStrength::Both("ndd"),
+                TargetFeatureFoldStrength::Both("ccmp"),
+                TargetFeatureFoldStrength::Both("cf"),
+                TargetFeatureFoldStrength::Both("nf"),
+                TargetFeatureFoldStrength::Both("zu"),
+            ],
+        )),
+        /*
+            Filter out features that are not supported by the current LLVM version.
+        */
+        ("aarch64", "fpmr") => None, // only existed in 18
+        ("loongarch32" | "loongarch64", "32s") if get_version().0 < 21 => None,
         ("loongarch64", "div32" | "lam-bh" | "lamcas" | "ld-seq-sa" | "scq")
             if get_version().0 < 20 =>
         {
             None
         }
-        ("loongarch32" | "loongarch64", "32s") if get_version().0 < 21 => None,
-        // Filter out features that are not supported by the current LLVM version
+        (
+            "nvptx64",
+            "sm_100" | "sm_100a" | "sm_101" | "sm_101a" | "sm_120" | "sm_120a" | "ptx86" | "ptx87",
+        ) if get_version().0 < 20 => None,
         ("riscv32" | "riscv64", "zacas" | "rva23u64" | "supm") if get_version().0 < 20 => None,
         (
             "s390x",
@@ -282,40 +295,32 @@ pub(crate) fn to_llvm_features<'a>(sess: &Session, s: &'a str) -> Option<LLVMFea
             | "vector-enhancements-3"
             | "vector-packed-decimal-enhancement-3",
         ) 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") => Some(LLVMFeature::with_dependencies(
-            s,
-            smallvec![TargetFeatureFoldStrength::EnableOnly("evex512")],
-        )),
-        // Support for `wide-arithmetic` will first land in LLVM 20 as part of
-        // llvm/llvm-project#111598
         ("wasm32" | "wasm64", "wide-arithmetic") if get_version().0 < 20 => None,
-        ("sparc", "leoncasa") => Some(LLVMFeature::new("hasleoncasa")),
+        (
+            "x86",
+            "amx-avx512" | "amx-fp8" | "amx-movrs" | "amx-tf32" | "amx-transpose" | "movrs",
+        ) if get_version().0 < 20 => None,
+        /*
+            Perform relatively complex feature conversion cases.
+        */
+        // Before LLVM 20 those two features were packaged together as b16b16
+        ("aarch64", "sve-b16b16" | "sme-b16b16") if get_version().0 < 20 => {
+            Some(LLVMFeature::new("b16b16"))
+        }
         // In LLVM 19, there is no `v8plus` feature and `v9` means "SPARC-V9 instruction available and SPARC-V8+ ABI used".
         // https://github.com/llvm/llvm-project/blob/llvmorg-19.1.0/llvm/lib/Target/Sparc/MCTargetDesc/SparcELFObjectWriter.cpp#L27-L28
         // Before LLVM 19, there was no `v8plus` feature and `v9` means "SPARC-V9 instruction available".
         // https://github.com/llvm/llvm-project/blob/llvmorg-18.1.0/llvm/lib/Target/Sparc/MCTargetDesc/SparcELFObjectWriter.cpp#L26
         ("sparc", "v8plus") if get_version().0 == 19 => Some(LLVMFeature::new("v9")),
-        ("powerpc", "power8-crypto") => Some(LLVMFeature::new("crypto")),
-        // These new `amx` variants and `movrs` were introduced in LLVM20
-        (
-            "x86",
-            "amx-avx512" | "amx-fp8" | "amx-movrs" | "amx-tf32" | "amx-transpose" | "movrs",
-        ) if get_version().0 < 20 => None,
-        ("x86", "avx10.1") => Some(LLVMFeature::new("avx10.1-512")),
-        ("x86", "avx10.2") => (get_version().0 >= 20).then(|| LLVMFeature::new("avx10.2-512")),
-        ("x86", "apxf") => Some(LLVMFeature::with_dependencies(
-            "egpr",
-            smallvec![
-                TargetFeatureFoldStrength::Both("push2pop2"),
-                TargetFeatureFoldStrength::Both("ppx"),
-                TargetFeatureFoldStrength::Both("ndd"),
-                TargetFeatureFoldStrength::Both("ccmp"),
-                TargetFeatureFoldStrength::Both("cf"),
-                TargetFeatureFoldStrength::Both("nf"),
-                TargetFeatureFoldStrength::Both("zu"),
-            ],
+        // Enable the evex512 target feature if an avx512 target feature is enabled.
+        ("x86", s) if s.starts_with("avx512") => Some(LLVMFeature::with_dependencies(
+            s,
+            smallvec![TargetFeatureFoldStrength::EnableOnly("evex512")],
         )),
+        ("x86", "avx10.2") => (get_version().0 >= 20).then(|| LLVMFeature::new("avx10.2-512")),
+        /*
+            By default, use the Rust's target feature name as-is.
+        */
         (_, s) => Some(LLVMFeature::new(s)),
     }
 }