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
7 use crate::abi::{FnAbi, FnAbiLlvmExt};
10 use crate::context::CodegenCx;
11 use crate::value::Value;
12 use rustc_codegen_ssa::traits::*;
14 use rustc::ty::{TypeFoldable, Instance};
15 use rustc::ty::layout::{FnAbiExt, 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 if let Some(&llfn) = cx.instances.borrow().get(&instance) {
40 let sym = tcx.symbol_name(instance).name.as_str();
41 debug!("get_fn({:?}: {:?}) => {}", instance, instance.ty(cx.tcx()), sym);
43 let fn_abi = FnAbi::of_instance(cx, instance, &[]);
45 let llfn = if let Some(llfn) = cx.get_declared_value(&sym) {
46 // Create a fn pointer with the new signature.
47 let llptrty = fn_abi.ptr_to_llvm_type(cx);
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, &fn_abi);
81 debug!("get_fn: not casting pointer!");
83 if instance.def.is_inline(tcx) {
84 attributes::inline(cx, llfn, attributes::InlineAttr::Hint);
86 // FIXME(eddyb) avoid this `Instance::fn_sig` call.
87 // Perhaps store the relevant information in `FnAbi`?
88 let sig_abi = instance.fn_sig(cx.tcx()).abi();
89 attributes::from_fn_attrs(cx, llfn, Some(instance.def.def_id()), sig_abi);
91 let instance_def_id = instance.def_id();
93 // Apply an appropriate linkage/visibility value to our item that we
96 // This is sort of subtle. Inside our codegen unit we started off
97 // compilation by predefining all our own `MonoItem` instances. That
98 // is, everything we're codegenning ourselves is already defined. That
99 // means that anything we're actually codegenning in this codegen unit
100 // will have hit the above branch in `get_declared_value`. As a result,
101 // we're guaranteed here that we're declaring a symbol that won't get
102 // defined, or in other words we're referencing a value from another
103 // codegen unit or even another crate.
105 // So because this is a foreign value we blanket apply an external
106 // linkage directive because it's coming from a different object file.
107 // The visibility here is where it gets tricky. This symbol could be
108 // referencing some foreign crate or foreign library (an `extern`
109 // block) in which case we want to leave the default visibility. We may
110 // also, though, have multiple codegen units. It could be a
111 // monomorphization, in which case its expected visibility depends on
112 // whether we are sharing generics or not. The important thing here is
113 // that the visibility we apply to the declaration is the same one that
114 // has been applied to the definition (wherever that definition may be).
116 llvm::LLVMRustSetLinkage(llfn, llvm::Linkage::ExternalLinkage);
118 let is_generic = instance.substs.non_erasable_generics().next().is_some();
121 // This is a monomorphization. Its expected visibility depends
122 // on whether we are in share-generics mode.
124 if cx.tcx.sess.opts.share_generics() {
125 // We are in share_generics mode.
127 if instance_def_id.is_local() {
128 // This is a definition from the current crate. If the
129 // definition is unreachable for downstream crates or
130 // the current crate does not re-export generics, the
131 // definition of the instance will have been declared
133 if cx.tcx.is_unreachable_local_definition(instance_def_id) ||
134 !cx.tcx.local_crate_exports_generics() {
135 llvm::LLVMRustSetVisibility(llfn, llvm::Visibility::Hidden);
138 // This is a monomorphization of a generic function
139 // defined in an upstream crate.
140 if cx.tcx.upstream_monomorphizations_for(instance_def_id)
141 .map(|set| set.contains_key(instance.substs))
143 // This is instantiated in another crate. It cannot
146 // This is a local instantiation of an upstream definition.
147 // If the current crate does not re-export it
148 // (because it is a C library or an executable), it
149 // will have been declared `hidden`.
150 if !cx.tcx.local_crate_exports_generics() {
151 llvm::LLVMRustSetVisibility(llfn, llvm::Visibility::Hidden);
156 // When not sharing generics, all instances are in the same
157 // crate and have hidden visibility
158 llvm::LLVMRustSetVisibility(llfn, llvm::Visibility::Hidden);
161 // This is a non-generic function
162 if cx.tcx.is_codegened_item(instance_def_id) {
163 // This is a function that is instantiated in the local crate
165 if instance_def_id.is_local() {
166 // This is function that is defined in the local crate.
167 // If it is not reachable, it is hidden.
168 if !cx.tcx.is_reachable_non_generic(instance_def_id) {
169 llvm::LLVMRustSetVisibility(llfn, llvm::Visibility::Hidden);
172 // This is a function from an upstream crate that has
173 // been instantiated here. These are always hidden.
174 llvm::LLVMRustSetVisibility(llfn, llvm::Visibility::Hidden);
180 if cx.use_dll_storage_attrs &&
181 tcx.is_dllimport_foreign_item(instance_def_id)
184 llvm::LLVMSetDLLStorageClass(llfn, llvm::DLLStorageClass::DllImport);
191 cx.instances.borrow_mut().insert(instance, llfn);