1 //! Handles codegen of callees as well as other call-related
2 //! things. Callees are a superset of normal rust values and sometimes
3 //! have different representations. In particular, top-level fn items
4 //! and methods are represented as just a fn ptr and not a full
9 use crate::monomorphize::Instance;
10 use crate::context::CodegenCx;
11 use crate::value::Value;
12 use rustc_codegen_ssa::traits::*;
14 use rustc::ty::TypeFoldable;
15 use rustc::ty::layout::{LayoutOf, HasTyCtxt};
17 /// Codegens a reference to a fn/method item, monomorphizing and
18 /// inlining as it goes.
22 /// - `cx`: the crate context
23 /// - `instance`: the instance to be instantiated
25 cx: &CodegenCx<'ll, 'tcx>,
26 instance: Instance<'tcx>,
30 debug!("get_fn(instance={:?})", instance);
32 assert!(!instance.substs.needs_infer());
33 assert!(!instance.substs.has_escaping_bound_vars());
34 assert!(!instance.substs.has_param_types());
36 let sig = instance.fn_sig(cx.tcx());
37 if let Some(&llfn) = cx.instances().borrow().get(&instance) {
41 let sym = tcx.symbol_name(instance).as_str();
42 debug!("get_fn({:?}: {:?}) => {}", instance, sig, sym);
44 // Create a fn pointer with the substituted signature.
45 let fn_ptr_ty = tcx.mk_fn_ptr(sig);
46 let llptrty = cx.backend_type(cx.layout_of(fn_ptr_ty));
48 let llfn = if let Some(llfn) = cx.get_declared_value(&sym) {
49 // This is subtle and surprising, but sometimes we have to bitcast
50 // the resulting fn pointer. The reason has to do with external
51 // functions. If you have two crates that both bind the same C
52 // library, they may not use precisely the same types: for
53 // example, they will probably each declare their own structs,
54 // which are distinct types from LLVM's point of view (nominal
57 // Now, if those two crates are linked into an application, and
58 // they contain inlined code, you can wind up with a situation
59 // where both of those functions wind up being loaded into this
60 // application simultaneously. In that case, the same function
61 // (from LLVM's point of view) requires two types. But of course
62 // LLVM won't allow one function to have two types.
64 // What we currently do, therefore, is declare the function with
65 // one of the two types (whichever happens to come first) and then
66 // bitcast as needed when the function is referenced to make sure
67 // it has the type we expect.
69 // This can occur on either a crate-local or crate-external
70 // reference. It also occurs when testing libcore and in some
71 // other weird situations. Annoying.
72 if cx.val_ty(llfn) != llptrty {
73 debug!("get_fn: casting {:?} to {:?}", llfn, llptrty);
74 cx.const_ptrcast(llfn, llptrty)
76 debug!("get_fn: not casting pointer!");
80 let llfn = cx.declare_fn(&sym, sig);
81 assert_eq!(cx.val_ty(llfn), llptrty);
82 debug!("get_fn: not casting pointer!");
84 if instance.def.is_inline(tcx) {
85 attributes::inline(cx, llfn, attributes::InlineAttr::Hint);
87 attributes::from_fn_attrs(cx, llfn, Some(instance.def.def_id()), sig);
89 let instance_def_id = instance.def_id();
91 // Apply an appropriate linkage/visibility value to our item that we
94 // This is sort of subtle. Inside our codegen unit we started off
95 // compilation by predefining all our own `MonoItem` instances. That
96 // is, everything we're codegenning ourselves is already defined. That
97 // means that anything we're actually codegenning in this codegen unit
98 // will have hit the above branch in `get_declared_value`. As a result,
99 // we're guaranteed here that we're declaring a symbol that won't get
100 // defined, or in other words we're referencing a value from another
101 // codegen unit or even another crate.
103 // So because this is a foreign value we blanket apply an external
104 // linkage directive because it's coming from a different object file.
105 // The visibility here is where it gets tricky. This symbol could be
106 // referencing some foreign crate or foreign library (an `extern`
107 // block) in which case we want to leave the default visibility. We may
108 // also, though, have multiple codegen units. It could be a
109 // monomorphization, in which case its expected visibility depends on
110 // whether we are sharing generics or not. The important thing here is
111 // that the visibility we apply to the declaration is the same one that
112 // has been applied to the definition (wherever that definition may be).
114 llvm::LLVMRustSetLinkage(llfn, llvm::Linkage::ExternalLinkage);
116 let is_generic = instance.substs.non_erasable_generics().next().is_some();
119 // This is a monomorphization. Its expected visibility depends
120 // on whether we are in share-generics mode.
122 if cx.tcx.sess.opts.share_generics() {
123 // We are in share_generics mode.
125 if instance_def_id.is_local() {
126 // This is a definition from the current crate. If the
127 // definition is unreachable for downstream crates or
128 // the current crate does not re-export generics, the
129 // definition of the instance will have been declared
131 if cx.tcx.is_unreachable_local_definition(instance_def_id) ||
132 !cx.tcx.local_crate_exports_generics() {
133 llvm::LLVMRustSetVisibility(llfn, llvm::Visibility::Hidden);
136 // This is a monomorphization of a generic function
137 // defined in an upstream crate.
138 if cx.tcx.upstream_monomorphizations_for(instance_def_id)
139 .map(|set| set.contains_key(instance.substs))
141 // This is instantiated in another crate. It cannot
144 // This is a local instantiation of an upstream definition.
145 // If the current crate does not re-export it
146 // (because it is a C library or an executable), it
147 // will have been declared `hidden`.
148 if !cx.tcx.local_crate_exports_generics() {
149 llvm::LLVMRustSetVisibility(llfn, llvm::Visibility::Hidden);
154 // When not sharing generics, all instances are in the same
155 // crate and have hidden visibility
156 llvm::LLVMRustSetVisibility(llfn, llvm::Visibility::Hidden);
159 // This is a non-generic function
160 if cx.tcx.is_codegened_item(instance_def_id) {
161 // This is a function that is instantiated in the local crate
163 if instance_def_id.is_local() {
164 // This is function that is defined in the local crate.
165 // If it is not reachable, it is hidden.
166 if !cx.tcx.is_reachable_non_generic(instance_def_id) {
167 llvm::LLVMRustSetVisibility(llfn, llvm::Visibility::Hidden);
170 // This is a function from an upstream crate that has
171 // been instantiated here. These are always hidden.
172 llvm::LLVMRustSetVisibility(llfn, llvm::Visibility::Hidden);
178 if cx.use_dll_storage_attrs &&
179 tcx.is_dllimport_foreign_item(instance_def_id)
182 llvm::LLVMSetDLLStorageClass(llfn, llvm::DLLStorageClass::DllImport);
189 cx.instances.borrow_mut().insert(instance, llfn);