compiler/rustc_codegen_llvm/src/llvm_util.rs - third_party/github.com/rust-lang/rust - Git at Google

 use crate::back::write::create_informational_target_machine;
 use crate::{llvm, llvm_util};
 use libc::c_int;
 use rustc_codegen_ssa::target_features::supported_target_features;
 use rustc_data_structures::fx::FxHashSet;
 use rustc_metadata::dynamic_lib::DynamicLibrary;
 use rustc_middle::bug;
 use rustc_session::config::PrintRequest;
 use rustc_session::Session;
 use rustc_span::symbol::Symbol;
 use rustc_target::spec::{MergeFunctions, PanicStrategy};
 use std::ffi::{CStr, CString};
 use tracing::debug;

 use std::mem;
 use std::path::Path;
 use std::ptr;
 use std::slice;
 use std::str;
 use std::sync::atomic::{AtomicBool, Ordering};
 use std::sync::Once;

 static POISONED: AtomicBool = AtomicBool::new(false);
 static INIT: Once = Once::new();

 pub(crate) fn init(sess: &Session) {
     unsafe {
         // Before we touch LLVM, make sure that multithreading is enabled.
         INIT.call_once(|| {
             if llvm::LLVMStartMultithreaded() != 1 {
                 // use an extra bool to make sure that all future usage of LLVM
                 // cannot proceed despite the Once not running more than once.
                 POISONED.store(true, Ordering::SeqCst);
             }

             configure_llvm(sess);
         });

         if POISONED.load(Ordering::SeqCst) {
             bug!("couldn't enable multi-threaded LLVM");
         }
     }
 }

 fn require_inited() {
     INIT.call_once(|| bug!("llvm is not initialized"));
     if POISONED.load(Ordering::SeqCst) {
         bug!("couldn't enable multi-threaded LLVM");
     }
 }

 unsafe fn configure_llvm(sess: &Session) {
     let n_args = sess.opts.cg.llvm_args.len() + sess.target.llvm_args.len();
     let mut llvm_c_strs = Vec::with_capacity(n_args + 1);
     let mut llvm_args = Vec::with_capacity(n_args + 1);

     llvm::LLVMRustInstallFatalErrorHandler();

     fn llvm_arg_to_arg_name(full_arg: &str) -> &str {
         full_arg.trim().split(|c: char| c == '=' || c.is_whitespace()).next().unwrap_or("")
     }

     let cg_opts = sess.opts.cg.llvm_args.iter();
     let tg_opts = sess.target.llvm_args.iter();
     let sess_args = cg_opts.chain(tg_opts);

     let user_specified_args: FxHashSet<_> =
         sess_args.clone().map(|s| llvm_arg_to_arg_name(s)).filter(|s| !s.is_empty()).collect();

     {
         // This adds the given argument to LLVM. Unless `force` is true
         // user specified arguments are *not* overridden.
         let mut add = |arg: &str, force: bool| {
             if force || !user_specified_args.contains(llvm_arg_to_arg_name(arg)) {
                 let s = CString::new(arg).unwrap();
                 llvm_args.push(s.as_ptr());
                 llvm_c_strs.push(s);
             }
         };
         // Set the llvm "program name" to make usage and invalid argument messages more clear.
         add("rustc -Cllvm-args=\"...\" with", true);
         if sess.time_llvm_passes() {
             add("-time-passes", false);
         }
         if sess.print_llvm_passes() {
             add("-debug-pass=Structure", false);
         }
         if !sess.opts.debugging_opts.no_generate_arange_section {
             add("-generate-arange-section", false);
         }

         // Disable the machine outliner by default in LLVM versions 11 and LLVM
         // version 12, where it leads to miscompilation.
         //
         // Ref:
         // - https://github.com/rust-lang/rust/issues/85351
         // - https://reviews.llvm.org/D103167
         let llvm_version = llvm_util::get_version();
         if llvm_version >= (11, 0, 0) && llvm_version < (13, 0, 0) {
             add("-enable-machine-outliner=never", false);
         }

         match sess.opts.debugging_opts.merge_functions.unwrap_or(sess.target.merge_functions) {
             MergeFunctions::Disabled | MergeFunctions::Trampolines => {}
             MergeFunctions::Aliases => {
                 add("-mergefunc-use-aliases", false);
             }
         }

         if sess.target.os == "emscripten" && sess.panic_strategy() == PanicStrategy::Unwind {
             add("-enable-emscripten-cxx-exceptions", false);
         }

         // HACK(eddyb) LLVM inserts `llvm.assume` calls to preserve align attributes
         // during inlining. Unfortunately these may block other optimizations.
         add("-preserve-alignment-assumptions-during-inlining=false", false);

         // Use non-zero `import-instr-limit` multiplier for cold callsites.
         add("-import-cold-multiplier=0.1", false);

         for arg in sess_args {
             add(&(*arg), true);
         }
     }

     if sess.opts.debugging_opts.llvm_time_trace {
         // time-trace is not thread safe and running it in parallel will cause seg faults.
         if !sess.opts.debugging_opts.no_parallel_llvm {
             bug!("`-Z llvm-time-trace` requires `-Z no-parallel-llvm")
         }

         llvm::LLVMTimeTraceProfilerInitialize();
     }

     llvm::LLVMInitializePasses();

     for plugin in &sess.opts.debugging_opts.llvm_plugins {
         let path = Path::new(plugin);
         let res = DynamicLibrary::open(path);
         match res {
             Ok(_) => debug!("LLVM plugin loaded succesfully {} ({})", path.display(), plugin),
             Err(e) => bug!("couldn't load plugin: {}", e),
         }
         mem::forget(res);
     }

     rustc_llvm::initialize_available_targets();

     llvm::LLVMRustSetLLVMOptions(llvm_args.len() as c_int, llvm_args.as_ptr());
 }

 pub fn time_trace_profiler_finish(file_name: &str) {
     unsafe {
         let file_name = CString::new(file_name).unwrap();
         llvm::LLVMTimeTraceProfilerFinish(file_name.as_ptr());
     }
 }

 // WARNING: the features after applying `to_llvm_feature` must be known
 // to LLVM or the feature detection code will walk past the end of the feature
 // array, leading to crashes.
 // To find a list of LLVM's names, check llvm-project/llvm/include/llvm/Support/*TargetParser.def
 // where the * matches the architecture's name
 // Beware to not use the llvm github project for this, but check the git submodule
 // found in src/llvm-project
 // Though note that Rust can also be build with an external precompiled version of LLVM
 // which might lead to failures if the oldest tested / supported LLVM version
 // doesn't yet support the relevant intrinsics
 pub fn to_llvm_feature<'a>(sess: &Session, s: &'a str) -> Vec<&'a str> {
     let arch = if sess.target.arch == "x86_64" { "x86" } else { &*sess.target.arch };
     match (arch, s) {
         ("x86", "sse4.2") => {
             if get_version() >= (14, 0, 0) {
                 vec!["sse4.2", "crc32"]
             } else {
                 vec!["sse4.2"]
             }
         }
         ("x86", "pclmulqdq") => vec!["pclmul"],
         ("x86", "rdrand") => vec!["rdrnd"],
         ("x86", "bmi1") => vec!["bmi"],
         ("x86", "cmpxchg16b") => vec!["cx16"],
         ("x86", "avx512vaes") => vec!["vaes"],
         ("x86", "avx512gfni") => vec!["gfni"],
         ("x86", "avx512vpclmulqdq") => vec!["vpclmulqdq"],
         ("aarch64", "fp") => vec!["fp-armv8"],
         ("aarch64", "fp16") => vec!["fullfp16"],
         ("aarch64", "fhm") => vec!["fp16fml"],
         ("aarch64", "rcpc2") => vec!["rcpc-immo"],
         ("aarch64", "dpb") => vec!["ccpp"],
         ("aarch64", "dpb2") => vec!["ccdp"],
         ("aarch64", "frintts") => vec!["fptoint"],
         ("aarch64", "fcma") => vec!["complxnum"],
         (_, s) => vec![s],
     }
 }

 pub fn target_features(sess: &Session) -> Vec<Symbol> {
     let target_machine = create_informational_target_machine(sess);
     supported_target_features(sess)
         .iter()
         .filter_map(
             |&(feature, gate)| {
                 if sess.is_nightly_build() || gate.is_none() { Some(feature) } else { None }
             },
         )
         .filter(|feature| {
             for llvm_feature in to_llvm_feature(sess, feature) {
                 let cstr = CString::new(llvm_feature).unwrap();
                 if unsafe { llvm::LLVMRustHasFeature(target_machine, cstr.as_ptr()) } {
                     return true;
                 }
             }
             false
         })
         .map(|feature| Symbol::intern(feature))
         .collect()
 }

 pub fn print_version() {
     let (major, minor, patch) = get_version();
     println!("LLVM version: {}.{}.{}", major, minor, patch);
 }

 pub fn get_version() -> (u32, u32, u32) {
     // Can be called without initializing LLVM
     unsafe {
         (llvm::LLVMRustVersionMajor(), llvm::LLVMRustVersionMinor(), llvm::LLVMRustVersionPatch())
     }
 }

 pub fn print_passes() {
     // Can be called without initializing LLVM
     unsafe {
         llvm::LLVMRustPrintPasses();
     }
 }

 fn llvm_target_features(tm: &llvm::TargetMachine) -> Vec<(&str, &str)> {
     let len = unsafe { llvm::LLVMRustGetTargetFeaturesCount(tm) };
     let mut ret = Vec::with_capacity(len);
     for i in 0..len {
         unsafe {
             let mut feature = ptr::null();
             let mut desc = ptr::null();
             llvm::LLVMRustGetTargetFeature(tm, i, &mut feature, &mut desc);
             if feature.is_null() || desc.is_null() {
                 bug!("LLVM returned a `null` target feature string");
             }
             let feature = CStr::from_ptr(feature).to_str().unwrap_or_else(|e| {
                 bug!("LLVM returned a non-utf8 feature string: {}", e);
             });
             let desc = CStr::from_ptr(desc).to_str().unwrap_or_else(|e| {
                 bug!("LLVM returned a non-utf8 feature string: {}", e);
             });
             ret.push((feature, desc));
         }
     }
     ret
 }

 fn print_target_features(sess: &Session, tm: &llvm::TargetMachine) {
     let mut target_features = llvm_target_features(tm);
     let mut rustc_target_features = supported_target_features(sess)
         .iter()
         .filter_map(|(feature, _gate)| {
             for llvm_feature in to_llvm_feature(sess, *feature) {
                 // LLVM asserts that these are sorted. LLVM and Rust both use byte comparison for these strings.
                 match target_features.binary_search_by_key(&llvm_feature, |(f, _d)| (*f)).ok().map(
                     |index| {
                         let (_f, desc) = target_features.remove(index);
                         (*feature, desc)
                     },
                 ) {
                     Some(v) => return Some(v),
                     None => {}
                 }
             }
             None
         })
         .collect::<Vec<_>>();
     rustc_target_features.extend_from_slice(&[(
         "crt-static",
         "Enables C Run-time Libraries to be statically linked",
     )]);
     let max_feature_len = target_features
         .iter()
         .chain(rustc_target_features.iter())
         .map(|(feature, _desc)| feature.len())
         .max()
         .unwrap_or(0);

     println!("Features supported by rustc for this target:");
     for (feature, desc) in &rustc_target_features {
         println!("    {1:0$} - {2}.", max_feature_len, feature, desc);
     }
     println!("\nCode-generation features supported by LLVM for this target:");
     for (feature, desc) in &target_features {
         println!("    {1:0$} - {2}.", max_feature_len, feature, desc);
     }
     if target_features.is_empty() {
         println!("    Target features listing is not supported by this LLVM version.");
     }
     println!("\nUse +feature to enable a feature, or -feature to disable it.");
     println!("For example, rustc -C target-cpu=mycpu -C target-feature=+feature1,-feature2\n");
     println!("Code-generation features cannot be used in cfg or #[target_feature],");
     println!("and may be renamed or removed in a future version of LLVM or rustc.\n");
 }

 pub(crate) fn print(req: PrintRequest, sess: &Session) {
     require_inited();
     let tm = create_informational_target_machine(sess);
     match req {
         PrintRequest::TargetCPUs => unsafe { llvm::LLVMRustPrintTargetCPUs(tm) },
         PrintRequest::TargetFeatures => print_target_features(sess, tm),
         _ => bug!("rustc_codegen_llvm can't handle print request: {:?}", req),
     }
 }

 fn handle_native(name: &str) -> &str {
     if name != "native" {
         return name;
     }

     unsafe {
         let mut len = 0;
         let ptr = llvm::LLVMRustGetHostCPUName(&mut len);
         str::from_utf8(slice::from_raw_parts(ptr as *const u8, len)).unwrap()
     }
 }

 pub fn target_cpu(sess: &Session) -> &str {
     let name = sess.opts.cg.target_cpu.as_ref().unwrap_or(&sess.target.cpu);
     handle_native(name)
 }

 /// The list of LLVM features computed from CLI flags (`-Ctarget-cpu`, `-Ctarget-feature`,
 /// `--target` and similar).
 // FIXME(nagisa): Cache the output of this somehow? Maybe make this a query? We're calling this
 // for every function that has `#[target_feature]` on it. The global features won't change between
 // the functions; only crates, maybe…
 pub fn llvm_global_features(sess: &Session) -> Vec<String> {
     // FIXME(nagisa): this should definitely be available more centrally and to other codegen backends.
     /// These features control behaviour of rustc rather than llvm.
     const RUSTC_SPECIFIC_FEATURES: &[&str] = &["crt-static"];

     // Features that come earlier are overriden by conflicting features later in the string.
     // Typically we'll want more explicit settings to override the implicit ones, so:
     //
     // * Features from -Ctarget-cpu=*; are overriden by [^1]
     // * Features implied by --target; are overriden by
     // * Features from -Ctarget-feature; are overriden by
     // * function specific features.
     //
     // [^1]: target-cpu=native is handled here, other target-cpu values are handled implicitly
     // through LLVM TargetMachine implementation.
     //
     // FIXME(nagisa): it isn't clear what's the best interaction between features implied by
     // `-Ctarget-cpu` and `--target` are. On one hand, you'd expect CLI arguments to always
     // override anything that's implicit, so e.g. when there's no `--target` flag, features implied
     // the host target are overriden by `-Ctarget-cpu=*`. On the other hand, what about when both
     // `--target` and `-Ctarget-cpu=*` are specified? Both then imply some target features and both
     // flags are specified by the user on the CLI. It isn't as clear-cut which order of precedence
     // should be taken in cases like these.
     let mut features = vec![];

     // -Ctarget-cpu=native
     match sess.opts.cg.target_cpu {
         Some(ref s) if s == "native" => {
             let features_string = unsafe {
                 let ptr = llvm::LLVMGetHostCPUFeatures();
                 let features_string = if !ptr.is_null() {
                     CStr::from_ptr(ptr)
                         .to_str()
                         .unwrap_or_else(|e| {
                             bug!("LLVM returned a non-utf8 features string: {}", e);
                         })
                         .to_owned()
                 } else {
                     bug!("could not allocate host CPU features, LLVM returned a `null` string");
                 };

                 llvm::LLVMDisposeMessage(ptr);

                 features_string
             };
             features.extend(features_string.split(',').map(String::from));
         }
         Some(_) | None => {}
     };

     let filter = |s: &str| {
         if s.is_empty() {
             return vec![];
         }
         let feature = if s.starts_with('+') || s.starts_with('-') {
             &s[1..]
         } else {
             return vec![s.to_string()];
         };
         // Rustc-specific feature requests like `+crt-static` or `-crt-static`
         // are not passed down to LLVM.
         if RUSTC_SPECIFIC_FEATURES.contains(&feature) {
             return vec![];
         }
         // ... otherwise though we run through `to_llvm_feature` feature when
         // passing requests down to LLVM. This means that all in-language
         // features also work on the command line instead of having two
         // different names when the LLVM name and the Rust name differ.
         to_llvm_feature(sess, feature).iter().map(|f| format!("{}{}", &s[..1], f)).collect()
     };

     // Features implied by an implicit or explicit `--target`.
     features.extend(sess.target.features.split(',').flat_map(&filter));

     // -Ctarget-features
     features.extend(sess.opts.cg.target_feature.split(',').flat_map(&filter));

     // FIXME: Move outline-atomics to target definition when earliest supported LLVM is 12.
     if get_version() >= (12, 0, 0)
         && sess.target.llvm_target.contains("aarch64-unknown-linux")
         && sess.target.llvm_target != "aarch64-unknown-linux-musl"
     {
         features.push("+outline-atomics".to_string());
     }

     features
 }

 pub fn tune_cpu(sess: &Session) -> Option<&str> {
     let name = sess.opts.debugging_opts.tune_cpu.as_ref()?;
     Some(handle_native(name))
 }
	use crate::back::write::create_informational_target_machine;
	use crate::{llvm, llvm_util};
	use libc::c_int;
	use rustc_codegen_ssa::target_features::supported_target_features;
	use rustc_data_structures::fx::FxHashSet;
	use rustc_metadata::dynamic_lib::DynamicLibrary;
	use rustc_middle::bug;
	use rustc_session::config::PrintRequest;
	use rustc_session::Session;
	use rustc_span::symbol::Symbol;
	use rustc_target::spec::{MergeFunctions, PanicStrategy};
	use std::ffi::{CStr, CString};
	use tracing::debug;

	use std::mem;
	use std::path::Path;
	use std::ptr;
	use std::slice;
	use std::str;
	use std::sync::atomic::{AtomicBool, Ordering};
	use std::sync::Once;

	static POISONED: AtomicBool = AtomicBool::new(false);
	static INIT: Once = Once::new();

	pub(crate) fn init(sess: &Session) {
	unsafe {
	// Before we touch LLVM, make sure that multithreading is enabled.
	INIT.call_once(\|\| {
	if llvm::LLVMStartMultithreaded() != 1 {
	// use an extra bool to make sure that all future usage of LLVM
	// cannot proceed despite the Once not running more than once.
	POISONED.store(true, Ordering::SeqCst);
	}

	configure_llvm(sess);
	});

	if POISONED.load(Ordering::SeqCst) {
	bug!("couldn't enable multi-threaded LLVM");
	}
	}
	}

	fn require_inited() {
	INIT.call_once(\|\| bug!("llvm is not initialized"));
	if POISONED.load(Ordering::SeqCst) {
	bug!("couldn't enable multi-threaded LLVM");
	}
	}

	unsafe fn configure_llvm(sess: &Session) {
	let n_args = sess.opts.cg.llvm_args.len() + sess.target.llvm_args.len();
	let mut llvm_c_strs = Vec::with_capacity(n_args + 1);
	let mut llvm_args = Vec::with_capacity(n_args + 1);

	llvm::LLVMRustInstallFatalErrorHandler();

	fn llvm_arg_to_arg_name(full_arg: &str) -> &str {
	full_arg.trim().split(\|c: char\| c == '=' \|\| c.is_whitespace()).next().unwrap_or("")
	}

	let cg_opts = sess.opts.cg.llvm_args.iter();
	let tg_opts = sess.target.llvm_args.iter();
	let sess_args = cg_opts.chain(tg_opts);

	let user_specified_args: FxHashSet<_> =
	sess_args.clone().map(\|s\| llvm_arg_to_arg_name(s)).filter(\|s\| !s.is_empty()).collect();

	{
	// This adds the given argument to LLVM. Unless `force` is true
	// user specified arguments are not overridden.
	let mut add = \|arg: &str, force: bool\| {
	if force \|\| !user_specified_args.contains(llvm_arg_to_arg_name(arg)) {
	let s = CString::new(arg).unwrap();
	llvm_args.push(s.as_ptr());
	llvm_c_strs.push(s);
	}
	};
	// Set the llvm "program name" to make usage and invalid argument messages more clear.
	add("rustc -Cllvm-args=\"...\" with", true);
	if sess.time_llvm_passes() {
	add("-time-passes", false);
	}
	if sess.print_llvm_passes() {
	add("-debug-pass=Structure", false);
	}
	if !sess.opts.debugging_opts.no_generate_arange_section {
	add("-generate-arange-section", false);
	}

	// Disable the machine outliner by default in LLVM versions 11 and LLVM
	// version 12, where it leads to miscompilation.
	//
	// Ref:
	// - https://github.com/rust-lang/rust/issues/85351
	// - https://reviews.llvm.org/D103167
	let llvm_version = llvm_util::get_version();
	if llvm_version >= (11, 0, 0) && llvm_version < (13, 0, 0) {
	add("-enable-machine-outliner=never", false);
	}

	match sess.opts.debugging_opts.merge_functions.unwrap_or(sess.target.merge_functions) {
	MergeFunctions::Disabled \| MergeFunctions::Trampolines => {}
	MergeFunctions::Aliases => {
	add("-mergefunc-use-aliases", false);
	}
	}

	if sess.target.os == "emscripten" && sess.panic_strategy() == PanicStrategy::Unwind {
	add("-enable-emscripten-cxx-exceptions", false);
	}

	// HACK(eddyb) LLVM inserts `llvm.assume` calls to preserve align attributes
	// during inlining. Unfortunately these may block other optimizations.
	add("-preserve-alignment-assumptions-during-inlining=false", false);

	// Use non-zero `import-instr-limit` multiplier for cold callsites.
	add("-import-cold-multiplier=0.1", false);

	for arg in sess_args {
	add(&(*arg), true);
	}
	}

	if sess.opts.debugging_opts.llvm_time_trace {
	// time-trace is not thread safe and running it in parallel will cause seg faults.
	if !sess.opts.debugging_opts.no_parallel_llvm {
	bug!("`-Z llvm-time-trace` requires `-Z no-parallel-llvm")
	}

	llvm::LLVMTimeTraceProfilerInitialize();
	}

	llvm::LLVMInitializePasses();

	for plugin in &sess.opts.debugging_opts.llvm_plugins {
	let path = Path::new(plugin);
	let res = DynamicLibrary::open(path);
	match res {
	Ok(_) => debug!("LLVM plugin loaded succesfully {} ({})", path.display(), plugin),
	Err(e) => bug!("couldn't load plugin: {}", e),
	}
	mem::forget(res);
	}

	rustc_llvm::initialize_available_targets();

	llvm::LLVMRustSetLLVMOptions(llvm_args.len() as c_int, llvm_args.as_ptr());
	}

	pub fn time_trace_profiler_finish(file_name: &str) {
	unsafe {
	let file_name = CString::new(file_name).unwrap();
	llvm::LLVMTimeTraceProfilerFinish(file_name.as_ptr());
	}
	}

	// WARNING: the features after applying `to_llvm_feature` must be known
	// to LLVM or the feature detection code will walk past the end of the feature
	// array, leading to crashes.
	// To find a list of LLVM's names, check llvm-project/llvm/include/llvm/Support/*TargetParser.def
	// where the * matches the architecture's name
	// Beware to not use the llvm github project for this, but check the git submodule
	// found in src/llvm-project
	// Though note that Rust can also be build with an external precompiled version of LLVM
	// which might lead to failures if the oldest tested / supported LLVM version
	// doesn't yet support the relevant intrinsics
	pub fn to_llvm_feature<'a>(sess: &Session, s: &'a str) -> Vec<&'a str> {
	let arch = if sess.target.arch == "x86_64" { "x86" } else { &*sess.target.arch };
	match (arch, s) {
	("x86", "sse4.2") => {
	if get_version() >= (14, 0, 0) {
	vec!["sse4.2", "crc32"]
	} else {
	vec!["sse4.2"]
	}
	}
	("x86", "pclmulqdq") => vec!["pclmul"],
	("x86", "rdrand") => vec!["rdrnd"],
	("x86", "bmi1") => vec!["bmi"],
	("x86", "cmpxchg16b") => vec!["cx16"],
	("x86", "avx512vaes") => vec!["vaes"],
	("x86", "avx512gfni") => vec!["gfni"],
	("x86", "avx512vpclmulqdq") => vec!["vpclmulqdq"],
	("aarch64", "fp") => vec!["fp-armv8"],
	("aarch64", "fp16") => vec!["fullfp16"],
	("aarch64", "fhm") => vec!["fp16fml"],
	("aarch64", "rcpc2") => vec!["rcpc-immo"],
	("aarch64", "dpb") => vec!["ccpp"],
	("aarch64", "dpb2") => vec!["ccdp"],
	("aarch64", "frintts") => vec!["fptoint"],
	("aarch64", "fcma") => vec!["complxnum"],
	(_, s) => vec![s],
	}
	}

	pub fn target_features(sess: &Session) -> Vec<Symbol> {
	let target_machine = create_informational_target_machine(sess);
	supported_target_features(sess)
	.iter()
	.filter_map(
	\|&(feature, gate)\| {
	if sess.is_nightly_build() \|\| gate.is_none() { Some(feature) } else { None }
	},
	)
	.filter(\|feature\| {
	for llvm_feature in to_llvm_feature(sess, feature) {
	let cstr = CString::new(llvm_feature).unwrap();
	if unsafe { llvm::LLVMRustHasFeature(target_machine, cstr.as_ptr()) } {
	return true;
	}
	}
	false
	})
	.map(\|feature\| Symbol::intern(feature))
	.collect()
	}

	pub fn print_version() {
	let (major, minor, patch) = get_version();
	println!("LLVM version: {}.{}.{}", major, minor, patch);
	}

	pub fn get_version() -> (u32, u32, u32) {
	// Can be called without initializing LLVM
	unsafe {
	(llvm::LLVMRustVersionMajor(), llvm::LLVMRustVersionMinor(), llvm::LLVMRustVersionPatch())
	}
	}

	pub fn print_passes() {
	// Can be called without initializing LLVM
	unsafe {
	llvm::LLVMRustPrintPasses();
	}
	}

	fn llvm_target_features(tm: &llvm::TargetMachine) -> Vec<(&str, &str)> {
	let len = unsafe { llvm::LLVMRustGetTargetFeaturesCount(tm) };
	let mut ret = Vec::with_capacity(len);
	for i in 0..len {
	unsafe {
	let mut feature = ptr::null();
	let mut desc = ptr::null();
	llvm::LLVMRustGetTargetFeature(tm, i, &mut feature, &mut desc);
	if feature.is_null() \|\| desc.is_null() {
	bug!("LLVM returned a `null` target feature string");
	}
	let feature = CStr::from_ptr(feature).to_str().unwrap_or_else(\|e\| {
	bug!("LLVM returned a non-utf8 feature string: {}", e);
	});
	let desc = CStr::from_ptr(desc).to_str().unwrap_or_else(\|e\| {
	bug!("LLVM returned a non-utf8 feature string: {}", e);
	});
	ret.push((feature, desc));
	}
	}
	ret
	}

	fn print_target_features(sess: &Session, tm: &llvm::TargetMachine) {
	let mut target_features = llvm_target_features(tm);
	let mut rustc_target_features = supported_target_features(sess)
	.iter()
	.filter_map(\|(feature, _gate)\| {
	for llvm_feature in to_llvm_feature(sess, *feature) {
	// LLVM asserts that these are sorted. LLVM and Rust both use byte comparison for these strings.
	match target_features.binary_search_by_key(&llvm_feature, \|(f, _d)\| (*f)).ok().map(
	\|index\| {
	let (_f, desc) = target_features.remove(index);
	(*feature, desc)
	},
	) {
	Some(v) => return Some(v),
	None => {}
	}
	}
	None
	})
	.collect::<Vec<_>>();
	rustc_target_features.extend_from_slice(&[(
	"crt-static",
	"Enables C Run-time Libraries to be statically linked",
	)]);
	let max_feature_len = target_features
	.iter()
	.chain(rustc_target_features.iter())
	.map(\|(feature, _desc)\| feature.len())
	.max()
	.unwrap_or(0);

	println!("Features supported by rustc for this target:");
	for (feature, desc) in &rustc_target_features {
	println!(" {1:0$} - {2}.", max_feature_len, feature, desc);
	}
	println!("\nCode-generation features supported by LLVM for this target:");
	for (feature, desc) in &target_features {
	println!(" {1:0$} - {2}.", max_feature_len, feature, desc);
	}
	if target_features.is_empty() {
	println!(" Target features listing is not supported by this LLVM version.");
	}
	println!("\nUse +feature to enable a feature, or -feature to disable it.");
	println!("For example, rustc -C target-cpu=mycpu -C target-feature=+feature1,-feature2\n");
	println!("Code-generation features cannot be used in cfg or #[target_feature],");
	println!("and may be renamed or removed in a future version of LLVM or rustc.\n");
	}

	pub(crate) fn print(req: PrintRequest, sess: &Session) {
	require_inited();
	let tm = create_informational_target_machine(sess);
	match req {
	PrintRequest::TargetCPUs => unsafe { llvm::LLVMRustPrintTargetCPUs(tm) },
	PrintRequest::TargetFeatures => print_target_features(sess, tm),
	_ => bug!("rustc_codegen_llvm can't handle print request: {:?}", req),
	}
	}

	fn handle_native(name: &str) -> &str {
	if name != "native" {
	return name;
	}

	unsafe {
	let mut len = 0;
	let ptr = llvm::LLVMRustGetHostCPUName(&mut len);
	str::from_utf8(slice::from_raw_parts(ptr as *const u8, len)).unwrap()
	}
	}

	pub fn target_cpu(sess: &Session) -> &str {
	let name = sess.opts.cg.target_cpu.as_ref().unwrap_or(&sess.target.cpu);
	handle_native(name)
	}

	/// The list of LLVM features computed from CLI flags (`-Ctarget-cpu`, `-Ctarget-feature`,
	/// `--target` and similar).
	// FIXME(nagisa): Cache the output of this somehow? Maybe make this a query? We're calling this
	// for every function that has `#[target_feature]` on it. The global features won't change between
	// the functions; only crates, maybe…
	pub fn llvm_global_features(sess: &Session) -> Vec<String> {
	// FIXME(nagisa): this should definitely be available more centrally and to other codegen backends.
	/// These features control behaviour of rustc rather than llvm.
	const RUSTC_SPECIFIC_FEATURES: &[&str] = &["crt-static"];

	// Features that come earlier are overriden by conflicting features later in the string.
	// Typically we'll want more explicit settings to override the implicit ones, so:
	//
	// * Features from -Ctarget-cpu=*; are overriden by [^1]
	// * Features implied by --target; are overriden by
	// * Features from -Ctarget-feature; are overriden by
	// * function specific features.
	//
	// [^1]: target-cpu=native is handled here, other target-cpu values are handled implicitly
	// through LLVM TargetMachine implementation.
	//
	// FIXME(nagisa): it isn't clear what's the best interaction between features implied by
	// `-Ctarget-cpu` and `--target` are. On one hand, you'd expect CLI arguments to always
	// override anything that's implicit, so e.g. when there's no `--target` flag, features implied
	// the host target are overriden by `-Ctarget-cpu=*`. On the other hand, what about when both
	// `--target` and `-Ctarget-cpu=*` are specified? Both then imply some target features and both
	// flags are specified by the user on the CLI. It isn't as clear-cut which order of precedence
	// should be taken in cases like these.
	let mut features = vec![];

	// -Ctarget-cpu=native
	match sess.opts.cg.target_cpu {
	Some(ref s) if s == "native" => {
	let features_string = unsafe {
	let ptr = llvm::LLVMGetHostCPUFeatures();
	let features_string = if !ptr.is_null() {
	CStr::from_ptr(ptr)
	.to_str()
	.unwrap_or_else(\|e\| {
	bug!("LLVM returned a non-utf8 features string: {}", e);
	})
	.to_owned()
	} else {
	bug!("could not allocate host CPU features, LLVM returned a `null` string");
	};

	llvm::LLVMDisposeMessage(ptr);

	features_string
	};
	features.extend(features_string.split(',').map(String::from));
	}
	Some(_) \| None => {}
	};

	let filter = \|s: &str\| {
	if s.is_empty() {
	return vec![];
	}
	let feature = if s.starts_with('+') \|\| s.starts_with('-') {
	&s[1..]
	} else {
	return vec![s.to_string()];
	};
	// Rustc-specific feature requests like `+crt-static` or `-crt-static`
	// are not passed down to LLVM.
	if RUSTC_SPECIFIC_FEATURES.contains(&feature) {
	return vec![];
	}
	// ... otherwise though we run through `to_llvm_feature` feature when
	// passing requests down to LLVM. This means that all in-language
	// features also work on the command line instead of having two
	// different names when the LLVM name and the Rust name differ.
	to_llvm_feature(sess, feature).iter().map(\|f\| format!("{}{}", &s[..1], f)).collect()
	};

	// Features implied by an implicit or explicit `--target`.
	features.extend(sess.target.features.split(',').flat_map(&filter));

	// -Ctarget-features
	features.extend(sess.opts.cg.target_feature.split(',').flat_map(&filter));

	// FIXME: Move outline-atomics to target definition when earliest supported LLVM is 12.
	if get_version() >= (12, 0, 0)
	&& sess.target.llvm_target.contains("aarch64-unknown-linux")
	&& sess.target.llvm_target != "aarch64-unknown-linux-musl"
	{
	features.push("+outline-atomics".to_string());
	}

	features
	}

	pub fn tune_cpu(sess: &Session) -> Option<&str> {
	let name = sess.opts.debugging_opts.tune_cpu.as_ref()?;
	Some(handle_native(name))
	}