1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
use crate::dep_graph::{DepConstructor, DepNode, WorkProduct, WorkProductId};
use crate::ich::{Fingerprint, NodeIdHashingMode, StableHashingContext};
use crate::session::config::OptLevel;
use crate::ty::print::obsolete::DefPathBasedNames;
use crate::ty::{subst::InternalSubsts, Instance, InstanceDef, SymbolName, TyCtxt};
use rustc_data_structures::base_n;
use rustc_data_structures::fx::FxHashMap;
use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
use rustc_hir::def_id::{CrateNum, DefId, LOCAL_CRATE};
use rustc_hir::HirId;
use rustc_span::source_map::Span;
use rustc_span::symbol::Symbol;
use std::fmt;
use std::hash::Hash;
use syntax::attr::InlineAttr;

/// Describes how a monomorphization will be instantiated in object files.
#[derive(PartialEq)]
pub enum InstantiationMode {
    /// There will be exactly one instance of the given MonoItem. It will have
    /// external linkage so that it can be linked to from other codegen units.
    GloballyShared {
        /// In some compilation scenarios we may decide to take functions that
        /// are typically `LocalCopy` and instead move them to `GloballyShared`
        /// to avoid codegenning them a bunch of times. In this situation,
        /// however, our local copy may conflict with other crates also
        /// inlining the same function.
        ///
        /// This flag indicates that this situation is occurring, and informs
        /// symbol name calculation that some extra mangling is needed to
        /// avoid conflicts. Note that this may eventually go away entirely if
        /// ThinLTO enables us to *always* have a globally shared instance of a
        /// function within one crate's compilation.
        may_conflict: bool,
    },

    /// Each codegen unit containing a reference to the given MonoItem will
    /// have its own private copy of the function (with internal linkage).
    LocalCopy,
}

#[derive(PartialEq, Eq, Clone, Copy, Debug, Hash)]
pub enum MonoItem<'tcx> {
    Fn(Instance<'tcx>),
    Static(DefId),
    GlobalAsm(HirId),
}

impl<'tcx> MonoItem<'tcx> {
    pub fn size_estimate(&self, tcx: TyCtxt<'tcx>) -> usize {
        match *self {
            MonoItem::Fn(instance) => {
                // Estimate the size of a function based on how many statements
                // it contains.
                tcx.instance_def_size_estimate(instance.def)
            }
            // Conservatively estimate the size of a static declaration
            // or assembly to be 1.
            MonoItem::Static(_) | MonoItem::GlobalAsm(_) => 1,
        }
    }

    pub fn is_generic_fn(&self) -> bool {
        match *self {
            MonoItem::Fn(ref instance) => instance.substs.non_erasable_generics().next().is_some(),
            MonoItem::Static(..) | MonoItem::GlobalAsm(..) => false,
        }
    }

    pub fn symbol_name(&self, tcx: TyCtxt<'tcx>) -> SymbolName {
        match *self {
            MonoItem::Fn(instance) => tcx.symbol_name(instance),
            MonoItem::Static(def_id) => tcx.symbol_name(Instance::mono(tcx, def_id)),
            MonoItem::GlobalAsm(hir_id) => {
                let def_id = tcx.hir().local_def_id(hir_id);
                SymbolName { name: Symbol::intern(&format!("global_asm_{:?}", def_id)) }
            }
        }
    }

    pub fn instantiation_mode(&self, tcx: TyCtxt<'tcx>) -> InstantiationMode {
        let generate_cgu_internal_copies = tcx
            .sess
            .opts
            .debugging_opts
            .inline_in_all_cgus
            .unwrap_or_else(|| tcx.sess.opts.optimize != OptLevel::No)
            && !tcx.sess.opts.cg.link_dead_code;

        match *self {
            MonoItem::Fn(ref instance) => {
                let entry_def_id = tcx.entry_fn(LOCAL_CRATE).map(|(id, _)| id);
                // If this function isn't inlined or otherwise has explicit
                // linkage, then we'll be creating a globally shared version.
                if self.explicit_linkage(tcx).is_some()
                    || !instance.def.generates_cgu_internal_copy(tcx)
                    || Some(instance.def_id()) == entry_def_id
                {
                    return InstantiationMode::GloballyShared { may_conflict: false };
                }

                // At this point we don't have explicit linkage and we're an
                // inlined function. If we're inlining into all CGUs then we'll
                // be creating a local copy per CGU
                if generate_cgu_internal_copies {
                    return InstantiationMode::LocalCopy;
                }

                // Finally, if this is `#[inline(always)]` we're sure to respect
                // that with an inline copy per CGU, but otherwise we'll be
                // creating one copy of this `#[inline]` function which may
                // conflict with upstream crates as it could be an exported
                // symbol.
                match tcx.codegen_fn_attrs(instance.def_id()).inline {
                    InlineAttr::Always => InstantiationMode::LocalCopy,
                    _ => InstantiationMode::GloballyShared { may_conflict: true },
                }
            }
            MonoItem::Static(..) | MonoItem::GlobalAsm(..) => {
                InstantiationMode::GloballyShared { may_conflict: false }
            }
        }
    }

    pub fn explicit_linkage(&self, tcx: TyCtxt<'tcx>) -> Option<Linkage> {
        let def_id = match *self {
            MonoItem::Fn(ref instance) => instance.def_id(),
            MonoItem::Static(def_id) => def_id,
            MonoItem::GlobalAsm(..) => return None,
        };

        let codegen_fn_attrs = tcx.codegen_fn_attrs(def_id);
        codegen_fn_attrs.linkage
    }

    /// Returns `true` if this instance is instantiable - whether it has no unsatisfied
    /// predicates.
    ///
    /// In order to codegen an item, all of its predicates must hold, because
    /// otherwise the item does not make sense. Type-checking ensures that
    /// the predicates of every item that is *used by* a valid item *do*
    /// hold, so we can rely on that.
    ///
    /// However, we codegen collector roots (reachable items) and functions
    /// in vtables when they are seen, even if they are not used, and so they
    /// might not be instantiable. For example, a programmer can define this
    /// public function:
    ///
    ///     pub fn foo<'a>(s: &'a mut ()) where &'a mut (): Clone {
    ///         <&mut () as Clone>::clone(&s);
    ///     }
    ///
    /// That function can't be codegened, because the method `<&mut () as Clone>::clone`
    /// does not exist. Luckily for us, that function can't ever be used,
    /// because that would require for `&'a mut (): Clone` to hold, so we
    /// can just not emit any code, or even a linker reference for it.
    ///
    /// Similarly, if a vtable method has such a signature, and therefore can't
    /// be used, we can just not emit it and have a placeholder (a null pointer,
    /// which will never be accessed) in its place.
    pub fn is_instantiable(&self, tcx: TyCtxt<'tcx>) -> bool {
        debug!("is_instantiable({:?})", self);
        let (def_id, substs) = match *self {
            MonoItem::Fn(ref instance) => (instance.def_id(), instance.substs),
            MonoItem::Static(def_id) => (def_id, InternalSubsts::empty()),
            // global asm never has predicates
            MonoItem::GlobalAsm(..) => return true,
        };

        tcx.substitute_normalize_and_test_predicates((def_id, &substs))
    }

    pub fn to_string(&self, tcx: TyCtxt<'tcx>, debug: bool) -> String {
        return match *self {
            MonoItem::Fn(instance) => to_string_internal(tcx, "fn ", instance, debug),
            MonoItem::Static(def_id) => {
                let instance = Instance::new(def_id, tcx.intern_substs(&[]));
                to_string_internal(tcx, "static ", instance, debug)
            }
            MonoItem::GlobalAsm(..) => "global_asm".to_string(),
        };

        fn to_string_internal<'tcx>(
            tcx: TyCtxt<'tcx>,
            prefix: &str,
            instance: Instance<'tcx>,
            debug: bool,
        ) -> String {
            let mut result = String::with_capacity(32);
            result.push_str(prefix);
            let printer = DefPathBasedNames::new(tcx, false, false);
            printer.push_instance_as_string(instance, &mut result, debug);
            result
        }
    }

    pub fn local_span(&self, tcx: TyCtxt<'tcx>) -> Option<Span> {
        match *self {
            MonoItem::Fn(Instance { def, .. }) => tcx.hir().as_local_hir_id(def.def_id()),
            MonoItem::Static(def_id) => tcx.hir().as_local_hir_id(def_id),
            MonoItem::GlobalAsm(hir_id) => Some(hir_id),
        }
        .map(|hir_id| tcx.hir().span(hir_id))
    }
}

impl<'a, 'tcx> HashStable<StableHashingContext<'a>> for MonoItem<'tcx> {
    fn hash_stable(&self, hcx: &mut StableHashingContext<'a>, hasher: &mut StableHasher) {
        ::std::mem::discriminant(self).hash_stable(hcx, hasher);

        match *self {
            MonoItem::Fn(ref instance) => {
                instance.hash_stable(hcx, hasher);
            }
            MonoItem::Static(def_id) => {
                def_id.hash_stable(hcx, hasher);
            }
            MonoItem::GlobalAsm(node_id) => {
                hcx.with_node_id_hashing_mode(NodeIdHashingMode::HashDefPath, |hcx| {
                    node_id.hash_stable(hcx, hasher);
                })
            }
        }
    }
}

pub struct CodegenUnit<'tcx> {
    /// A name for this CGU. Incremental compilation requires that
    /// name be unique amongst **all** crates. Therefore, it should
    /// contain something unique to this crate (e.g., a module path)
    /// as well as the crate name and disambiguator.
    name: Symbol,
    items: FxHashMap<MonoItem<'tcx>, (Linkage, Visibility)>,
    size_estimate: Option<usize>,
}

#[derive(Copy, Clone, PartialEq, Debug, RustcEncodable, RustcDecodable, HashStable)]
pub enum Linkage {
    External,
    AvailableExternally,
    LinkOnceAny,
    LinkOnceODR,
    WeakAny,
    WeakODR,
    Appending,
    Internal,
    Private,
    ExternalWeak,
    Common,
}

#[derive(Copy, Clone, PartialEq, Debug, HashStable)]
pub enum Visibility {
    Default,
    Hidden,
    Protected,
}

impl<'tcx> CodegenUnit<'tcx> {
    pub fn new(name: Symbol) -> CodegenUnit<'tcx> {
        CodegenUnit { name: name, items: Default::default(), size_estimate: None }
    }

    pub fn name(&self) -> Symbol {
        self.name
    }

    pub fn set_name(&mut self, name: Symbol) {
        self.name = name;
    }

    pub fn items(&self) -> &FxHashMap<MonoItem<'tcx>, (Linkage, Visibility)> {
        &self.items
    }

    pub fn items_mut(&mut self) -> &mut FxHashMap<MonoItem<'tcx>, (Linkage, Visibility)> {
        &mut self.items
    }

    pub fn mangle_name(human_readable_name: &str) -> String {
        // We generate a 80 bit hash from the name. This should be enough to
        // avoid collisions and is still reasonably short for filenames.
        let mut hasher = StableHasher::new();
        human_readable_name.hash(&mut hasher);
        let hash: u128 = hasher.finish();
        let hash = hash & ((1u128 << 80) - 1);
        base_n::encode(hash, base_n::CASE_INSENSITIVE)
    }

    pub fn estimate_size(&mut self, tcx: TyCtxt<'tcx>) {
        // Estimate the size of a codegen unit as (approximately) the number of MIR
        // statements it corresponds to.
        self.size_estimate = Some(self.items.keys().map(|mi| mi.size_estimate(tcx)).sum());
    }

    pub fn size_estimate(&self) -> usize {
        // Should only be called if `estimate_size` has previously been called.
        self.size_estimate.expect("estimate_size must be called before getting a size_estimate")
    }

    pub fn modify_size_estimate(&mut self, delta: usize) {
        assert!(self.size_estimate.is_some());
        if let Some(size_estimate) = self.size_estimate {
            self.size_estimate = Some(size_estimate + delta);
        }
    }

    pub fn contains_item(&self, item: &MonoItem<'tcx>) -> bool {
        self.items().contains_key(item)
    }

    pub fn work_product_id(&self) -> WorkProductId {
        WorkProductId::from_cgu_name(&self.name().as_str())
    }

    pub fn work_product(&self, tcx: TyCtxt<'_>) -> WorkProduct {
        let work_product_id = self.work_product_id();
        tcx.dep_graph
            .previous_work_product(&work_product_id)
            .unwrap_or_else(|| panic!("Could not find work-product for CGU `{}`", self.name()))
    }

    pub fn items_in_deterministic_order(
        &self,
        tcx: TyCtxt<'tcx>,
    ) -> Vec<(MonoItem<'tcx>, (Linkage, Visibility))> {
        // The codegen tests rely on items being process in the same order as
        // they appear in the file, so for local items, we sort by node_id first
        #[derive(PartialEq, Eq, PartialOrd, Ord)]
        pub struct ItemSortKey(Option<HirId>, SymbolName);

        fn item_sort_key<'tcx>(tcx: TyCtxt<'tcx>, item: MonoItem<'tcx>) -> ItemSortKey {
            ItemSortKey(
                match item {
                    MonoItem::Fn(ref instance) => {
                        match instance.def {
                            // We only want to take HirIds of user-defined
                            // instances into account. The others don't matter for
                            // the codegen tests and can even make item order
                            // unstable.
                            InstanceDef::Item(def_id) => tcx.hir().as_local_hir_id(def_id),
                            InstanceDef::VtableShim(..)
                            | InstanceDef::ReifyShim(..)
                            | InstanceDef::Intrinsic(..)
                            | InstanceDef::FnPtrShim(..)
                            | InstanceDef::Virtual(..)
                            | InstanceDef::ClosureOnceShim { .. }
                            | InstanceDef::DropGlue(..)
                            | InstanceDef::CloneShim(..) => None,
                        }
                    }
                    MonoItem::Static(def_id) => tcx.hir().as_local_hir_id(def_id),
                    MonoItem::GlobalAsm(hir_id) => Some(hir_id),
                },
                item.symbol_name(tcx),
            )
        }

        let mut items: Vec<_> = self.items().iter().map(|(&i, &l)| (i, l)).collect();
        items.sort_by_cached_key(|&(i, _)| item_sort_key(tcx, i));
        items
    }

    pub fn codegen_dep_node(&self, tcx: TyCtxt<'tcx>) -> DepNode {
        DepNode::new(tcx, DepConstructor::CompileCodegenUnit(self.name().clone()))
    }
}

impl<'a, 'tcx> HashStable<StableHashingContext<'a>> for CodegenUnit<'tcx> {
    fn hash_stable(&self, hcx: &mut StableHashingContext<'a>, hasher: &mut StableHasher) {
        let CodegenUnit {
            ref items,
            name,
            // The size estimate is not relevant to the hash
            size_estimate: _,
        } = *self;

        name.hash_stable(hcx, hasher);

        let mut items: Vec<(Fingerprint, _)> = items
            .iter()
            .map(|(mono_item, &attrs)| {
                let mut hasher = StableHasher::new();
                mono_item.hash_stable(hcx, &mut hasher);
                let mono_item_fingerprint = hasher.finish();
                (mono_item_fingerprint, attrs)
            })
            .collect();

        items.sort_unstable_by_key(|i| i.0);
        items.hash_stable(hcx, hasher);
    }
}

pub struct CodegenUnitNameBuilder<'tcx> {
    tcx: TyCtxt<'tcx>,
    cache: FxHashMap<CrateNum, String>,
}

impl CodegenUnitNameBuilder<'tcx> {
    pub fn new(tcx: TyCtxt<'tcx>) -> Self {
        CodegenUnitNameBuilder { tcx, cache: Default::default() }
    }

    /// CGU names should fulfill the following requirements:
    /// - They should be able to act as a file name on any kind of file system
    /// - They should not collide with other CGU names, even for different versions
    ///   of the same crate.
    ///
    /// Consequently, we don't use special characters except for '.' and '-' and we
    /// prefix each name with the crate-name and crate-disambiguator.
    ///
    /// This function will build CGU names of the form:
    ///
    /// ```
    /// <crate-name>.<crate-disambiguator>[-in-<local-crate-id>](-<component>)*[.<special-suffix>]
    /// <local-crate-id> = <local-crate-name>.<local-crate-disambiguator>
    /// ```
    ///
    /// The '.' before `<special-suffix>` makes sure that names with a special
    /// suffix can never collide with a name built out of regular Rust
    /// identifiers (e.g., module paths).
    pub fn build_cgu_name<I, C, S>(
        &mut self,
        cnum: CrateNum,
        components: I,
        special_suffix: Option<S>,
    ) -> Symbol
    where
        I: IntoIterator<Item = C>,
        C: fmt::Display,
        S: fmt::Display,
    {
        let cgu_name = self.build_cgu_name_no_mangle(cnum, components, special_suffix);

        if self.tcx.sess.opts.debugging_opts.human_readable_cgu_names {
            cgu_name
        } else {
            let cgu_name = &cgu_name.as_str();
            Symbol::intern(&CodegenUnit::mangle_name(cgu_name))
        }
    }

    /// Same as `CodegenUnit::build_cgu_name()` but will never mangle the
    /// resulting name.
    pub fn build_cgu_name_no_mangle<I, C, S>(
        &mut self,
        cnum: CrateNum,
        components: I,
        special_suffix: Option<S>,
    ) -> Symbol
    where
        I: IntoIterator<Item = C>,
        C: fmt::Display,
        S: fmt::Display,
    {
        use std::fmt::Write;

        let mut cgu_name = String::with_capacity(64);

        // Start out with the crate name and disambiguator
        let tcx = self.tcx;
        let crate_prefix = self.cache.entry(cnum).or_insert_with(|| {
            // Whenever the cnum is not LOCAL_CRATE we also mix in the
            // local crate's ID. Otherwise there can be collisions between CGUs
            // instantiating stuff for upstream crates.
            let local_crate_id = if cnum != LOCAL_CRATE {
                let local_crate_disambiguator = format!("{}", tcx.crate_disambiguator(LOCAL_CRATE));
                format!("-in-{}.{}", tcx.crate_name(LOCAL_CRATE), &local_crate_disambiguator[0..8])
            } else {
                String::new()
            };

            let crate_disambiguator = tcx.crate_disambiguator(cnum).to_string();
            // Using a shortened disambiguator of about 40 bits
            format!("{}.{}{}", tcx.crate_name(cnum), &crate_disambiguator[0..8], local_crate_id)
        });

        write!(cgu_name, "{}", crate_prefix).unwrap();

        // Add the components
        for component in components {
            write!(cgu_name, "-{}", component).unwrap();
        }

        if let Some(special_suffix) = special_suffix {
            // We add a dot in here so it cannot clash with anything in a regular
            // Rust identifier
            write!(cgu_name, ".{}", special_suffix).unwrap();
        }

        Symbol::intern(&cgu_name[..])
    }
}