1 //! Set and unset common attributes on LLVM values.
5 use rustc::hir::{CodegenFnAttrFlags, CodegenFnAttrs};
6 use rustc::hir::def_id::{DefId, LOCAL_CRATE};
7 use rustc::session::Session;
8 use rustc::session::config::{Sanitizer, OptLevel};
9 use rustc::ty::{self, TyCtxt, PolyFnSig};
10 use rustc::ty::layout::HasTyCtxt;
11 use rustc::ty::query::Providers;
12 use rustc_data_structures::small_c_str::SmallCStr;
13 use rustc_data_structures::fx::FxHashMap;
14 use rustc_target::spec::PanicStrategy;
15 use rustc_codegen_ssa::traits::*;
18 use crate::attributes;
19 use crate::llvm::{self, Attribute};
20 use crate::llvm::AttributePlace::Function;
22 pub use syntax::attr::{self, InlineAttr, OptimizeAttr};
24 use crate::context::CodegenCx;
25 use crate::value::Value;
27 /// Mark LLVM function to use provided inline heuristic.
29 pub fn inline(cx: &CodegenCx<'ll, '_>, val: &'ll Value, inline: InlineAttr) {
30 use self::InlineAttr::*;
32 Hint => Attribute::InlineHint.apply_llfn(Function, val),
33 Always => Attribute::AlwaysInline.apply_llfn(Function, val),
35 if cx.tcx().sess.target.target.arch != "amdgpu" {
36 Attribute::NoInline.apply_llfn(Function, val);
40 Attribute::InlineHint.unapply_llfn(Function, val);
41 Attribute::AlwaysInline.unapply_llfn(Function, val);
42 Attribute::NoInline.unapply_llfn(Function, val);
47 /// Tell LLVM to emit or not emit the information necessary to unwind the stack for the function.
49 pub fn emit_uwtable(val: &'ll Value, emit: bool) {
50 Attribute::UWTable.toggle_llfn(Function, val, emit);
53 /// Tell LLVM whether the function can or cannot unwind.
55 fn unwind(val: &'ll Value, can_unwind: bool) {
56 Attribute::NoUnwind.toggle_llfn(Function, val, !can_unwind);
59 /// Tell LLVM if this function should be 'naked', i.e., skip the epilogue and prologue.
61 pub fn naked(val: &'ll Value, is_naked: bool) {
62 Attribute::Naked.toggle_llfn(Function, val, is_naked);
65 pub fn set_frame_pointer_elimination(cx: &CodegenCx<'ll, '_>, llfn: &'ll Value) {
66 if cx.sess().must_not_eliminate_frame_pointers() {
67 llvm::AddFunctionAttrStringValue(
68 llfn, llvm::AttributePlace::Function,
69 const_cstr!("no-frame-pointer-elim"), const_cstr!("true"));
73 /// Tell LLVM what instrument function to insert.
75 pub fn set_instrument_function(cx: &CodegenCx<'ll, '_>, llfn: &'ll Value) {
76 if cx.sess().instrument_mcount() {
77 // Similar to `clang -pg` behavior. Handled by the
78 // `post-inline-ee-instrument` LLVM pass.
80 // The function name varies on platforms.
81 // See test/CodeGen/mcount.c in clang.
82 let mcount_name = CString::new(
83 cx.sess().target.target.options.target_mcount.as_str().as_bytes()).unwrap();
85 llvm::AddFunctionAttrStringValue(
86 llfn, llvm::AttributePlace::Function,
87 const_cstr!("instrument-function-entry-inlined"), &mcount_name);
91 pub fn set_probestack(cx: &CodegenCx<'ll, '_>, llfn: &'ll Value) {
92 // Only use stack probes if the target specification indicates that we
93 // should be using stack probes
94 if !cx.sess().target.target.options.stack_probes {
98 // Currently stack probes seem somewhat incompatible with the address
99 // sanitizer and thread sanitizer. With asan we're already protected from
100 // stack overflow anyway so we don't really need stack probes regardless.
101 match cx.sess().opts.debugging_opts.sanitizer {
102 Some(Sanitizer::Address) |
103 Some(Sanitizer::Thread) => return,
107 // probestack doesn't play nice either with `-C profile-generate`.
108 if cx.sess().opts.cg.profile_generate.enabled() {
112 // probestack doesn't play nice either with gcov profiling.
113 if cx.sess().opts.debugging_opts.profile {
117 // Flag our internal `__rust_probestack` function as the stack probe symbol.
118 // This is defined in the `compiler-builtins` crate for each architecture.
119 llvm::AddFunctionAttrStringValue(
120 llfn, llvm::AttributePlace::Function,
121 const_cstr!("probe-stack"), const_cstr!("__rust_probestack"));
124 fn translate_obsolete_target_features(feature: &str) -> &str {
125 const LLVM9_FEATURE_CHANGES: &[(&str, &str)] = &[
126 ("+fp-only-sp", "-fp64"),
127 ("-fp-only-sp", "+fp64"),
131 if llvm_util::get_major_version() >= 9 {
132 for &(old, new) in LLVM9_FEATURE_CHANGES {
138 for &(old, new) in LLVM9_FEATURE_CHANGES {
147 pub fn llvm_target_features(sess: &Session) -> impl Iterator<Item = &str> {
148 const RUSTC_SPECIFIC_FEATURES: &[&str] = &[
152 let cmdline = sess.opts.cg.target_feature.split(',')
153 .filter(|f| !RUSTC_SPECIFIC_FEATURES.iter().any(|s| f.contains(s)));
154 sess.target.target.options.features.split(',')
156 .filter(|l| !l.is_empty())
157 .map(translate_obsolete_target_features)
160 pub fn apply_target_cpu_attr(cx: &CodegenCx<'ll, '_>, llfn: &'ll Value) {
161 let target_cpu = SmallCStr::new(llvm_util::target_cpu(cx.tcx.sess));
162 llvm::AddFunctionAttrStringValue(
164 llvm::AttributePlace::Function,
165 const_cstr!("target-cpu"),
166 target_cpu.as_c_str());
169 /// Sets the `NonLazyBind` LLVM attribute on a given function,
170 /// assuming the codegen options allow skipping the PLT.
171 pub fn non_lazy_bind(sess: &Session, llfn: &'ll Value) {
172 // Don't generate calls through PLT if it's not necessary
173 if !sess.needs_plt() {
174 Attribute::NonLazyBind.apply_llfn(Function, llfn);
178 pub(crate) fn default_optimisation_attrs(sess: &Session, llfn: &'ll Value) {
179 match sess.opts.optimize {
181 llvm::Attribute::MinSize.unapply_llfn(Function, llfn);
182 llvm::Attribute::OptimizeForSize.apply_llfn(Function, llfn);
183 llvm::Attribute::OptimizeNone.unapply_llfn(Function, llfn);
185 OptLevel::SizeMin => {
186 llvm::Attribute::MinSize.apply_llfn(Function, llfn);
187 llvm::Attribute::OptimizeForSize.apply_llfn(Function, llfn);
188 llvm::Attribute::OptimizeNone.unapply_llfn(Function, llfn);
191 llvm::Attribute::MinSize.unapply_llfn(Function, llfn);
192 llvm::Attribute::OptimizeForSize.unapply_llfn(Function, llfn);
193 llvm::Attribute::OptimizeNone.unapply_llfn(Function, llfn);
200 /// Composite function which sets LLVM attributes for function depending on its AST (`#[attribute]`)
202 pub fn from_fn_attrs(
203 cx: &CodegenCx<'ll, 'tcx>,
206 sig: PolyFnSig<'tcx>,
208 let codegen_fn_attrs = id.map(|id| cx.tcx.codegen_fn_attrs(id))
209 .unwrap_or_else(|| CodegenFnAttrs::new());
211 match codegen_fn_attrs.optimize {
212 OptimizeAttr::None => {
213 default_optimisation_attrs(cx.tcx.sess, llfn);
215 OptimizeAttr::Speed => {
216 llvm::Attribute::MinSize.unapply_llfn(Function, llfn);
217 llvm::Attribute::OptimizeForSize.unapply_llfn(Function, llfn);
218 llvm::Attribute::OptimizeNone.unapply_llfn(Function, llfn);
220 OptimizeAttr::Size => {
221 llvm::Attribute::MinSize.apply_llfn(Function, llfn);
222 llvm::Attribute::OptimizeForSize.apply_llfn(Function, llfn);
223 llvm::Attribute::OptimizeNone.unapply_llfn(Function, llfn);
227 inline(cx, llfn, codegen_fn_attrs.inline);
229 // The `uwtable` attribute according to LLVM is:
231 // This attribute indicates that the ABI being targeted requires that an
232 // unwind table entry be produced for this function even if we can show
233 // that no exceptions passes by it. This is normally the case for the
234 // ELF x86-64 abi, but it can be disabled for some compilation units.
236 // Typically when we're compiling with `-C panic=abort` (which implies this
237 // `no_landing_pads` check) we don't need `uwtable` because we can't
238 // generate any exceptions! On Windows, however, exceptions include other
239 // events such as illegal instructions, segfaults, etc. This means that on
240 // Windows we end up still needing the `uwtable` attribute even if the `-C
241 // panic=abort` flag is passed.
243 // You can also find more info on why Windows is whitelisted here in:
244 // https://bugzilla.mozilla.org/show_bug.cgi?id=1302078
245 if !cx.sess().no_landing_pads() ||
246 cx.sess().target.target.options.requires_uwtable {
247 attributes::emit_uwtable(llfn, true);
250 set_frame_pointer_elimination(cx, llfn);
251 set_instrument_function(cx, llfn);
252 set_probestack(cx, llfn);
254 if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::COLD) {
255 Attribute::Cold.apply_llfn(Function, llfn);
257 if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::FFI_RETURNS_TWICE) {
258 Attribute::ReturnsTwice.apply_llfn(Function, llfn);
260 if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::NAKED) {
263 if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::ALLOCATOR) {
264 Attribute::NoAlias.apply_llfn(
265 llvm::AttributePlace::ReturnValue, llfn);
268 unwind(llfn, if cx.tcx.sess.panic_strategy() != PanicStrategy::Unwind {
269 // In panic=abort mode we assume nothing can unwind anywhere, so
270 // optimize based on this!
272 } else if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::UNWIND) {
273 // If a specific #[unwind] attribute is present, use that.
275 } else if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::RUSTC_ALLOCATOR_NOUNWIND) {
276 // Special attribute for allocator functions, which can't unwind.
279 let sig = cx.tcx.normalize_erasing_late_bound_regions(ty::ParamEnv::reveal_all(), &sig);
280 if sig.abi == Abi::Rust || sig.abi == Abi::RustCall {
281 // Any Rust method (or `extern "Rust" fn` or `extern
282 // "rust-call" fn`) is explicitly allowed to unwind
283 // (unless it has no-unwind attribute, handled above).
286 // Anything else is either:
288 // 1. A foreign item using a non-Rust ABI (like `extern "C" { fn foo(); }`), or
290 // 2. A Rust item using a non-Rust ABI (like `extern "C" fn foo() { ... }`).
292 // Foreign items (case 1) are assumed to not unwind; it is
293 // UB otherwise. (At least for now; see also
294 // rust-lang/rust#63909 and Rust RFC 2753.)
296 // Items defined in Rust with non-Rust ABIs (case 2) are also
297 // not supposed to unwind. Whether this should be enforced
298 // (versus stating it is UB) and *how* it would be enforced
299 // is currently under discussion; see rust-lang/rust#58794.
301 // In either case, we mark item as explicitly nounwind.
306 // Always annotate functions with the target-cpu they are compiled for.
307 // Without this, ThinLTO won't inline Rust functions into Clang generated
308 // functions (because Clang annotates functions this way too).
309 apply_target_cpu_attr(cx, llfn);
311 let features = llvm_target_features(cx.tcx.sess)
312 .map(|s| s.to_string())
314 codegen_fn_attrs.target_features
317 let feature = &f.as_str();
318 format!("+{}", llvm_util::to_llvm_feature(cx.tcx.sess, feature))
321 .collect::<Vec<String>>()
324 if !features.is_empty() {
325 let val = CString::new(features).unwrap();
326 llvm::AddFunctionAttrStringValue(
327 llfn, llvm::AttributePlace::Function,
328 const_cstr!("target-features"), &val);
331 // Note that currently the `wasm-import-module` doesn't do anything, but
332 // eventually LLVM 7 should read this and ferry the appropriate import
333 // module to the output file.
334 if let Some(id) = id {
335 if cx.tcx.sess.target.target.arch == "wasm32" {
336 if let Some(module) = wasm_import_module(cx.tcx, id) {
337 llvm::AddFunctionAttrStringValue(
339 llvm::AttributePlace::Function,
340 const_cstr!("wasm-import-module"),
348 pub fn provide(providers: &mut Providers<'_>) {
349 providers.target_features_whitelist = |tcx, cnum| {
350 assert_eq!(cnum, LOCAL_CRATE);
351 if tcx.sess.opts.actually_rustdoc {
352 // rustdoc needs to be able to document functions that use all the features, so
353 // whitelist them all
354 tcx.arena.alloc(llvm_util::all_known_features()
355 .map(|(a, b)| (a.to_string(), b))
358 tcx.arena.alloc(llvm_util::target_feature_whitelist(tcx.sess)
360 .map(|&(a, b)| (a.to_string(), b))
365 provide_extern(providers);
368 pub fn provide_extern(providers: &mut Providers<'_>) {
369 providers.wasm_import_module_map = |tcx, cnum| {
370 // Build up a map from DefId to a `NativeLibrary` structure, where
371 // `NativeLibrary` internally contains information about
372 // `#[link(wasm_import_module = "...")]` for example.
373 let native_libs = tcx.native_libraries(cnum);
375 let def_id_to_native_lib = native_libs.iter().filter_map(|lib|
376 if let Some(id) = lib.foreign_module {
381 ).collect::<FxHashMap<_, _>>();
383 let mut ret = FxHashMap::default();
384 for lib in tcx.foreign_modules(cnum).iter() {
385 let module = def_id_to_native_lib
387 .and_then(|s| s.wasm_import_module);
388 let module = match module {
392 ret.extend(lib.foreign_items.iter().map(|id| {
393 assert_eq!(id.krate, cnum);
394 (*id, module.to_string())
402 fn wasm_import_module(tcx: TyCtxt<'_>, id: DefId) -> Option<CString> {
403 tcx.wasm_import_module_map(id.krate)
405 .map(|s| CString::new(&s[..]).unwrap())