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::*;
15 use rustc::ty::{TypeFoldable, Instance};
16 use rustc::ty::layout::{FnAbiExt, HasTyCtxt};
18 /// Codegens a reference to a fn/method item, monomorphizing and
19 /// inlining as it goes.
23 /// - `cx`: the crate context
24 /// - `instance`: the instance to be instantiated
26 cx: &CodegenCx<'ll, 'tcx>,
27 instance: Instance<'tcx>,
31 debug!("get_fn(instance={:?})", instance);
33 assert!(!instance.substs.needs_infer());
34 assert!(!instance.substs.has_escaping_bound_vars());
35 assert!(!instance.substs.has_param_types());
37 if let Some(&llfn) = cx.instances.borrow().get(&instance) {
41 let sym = tcx.symbol_name(instance).name.as_str();
42 debug!("get_fn({:?}: {:?}) => {}", instance, instance.ty(cx.tcx()), sym);
44 let fn_abi = FnAbi::of_instance(cx, instance, &[]);
46 let llfn = if let Some(llfn) = cx.get_declared_value(&sym) {
47 // Create a fn pointer with the new signature.
48 let llptrty = fn_abi.ptr_to_llvm_type(cx);
50 // This is subtle and surprising, but sometimes we have to bitcast
51 // the resulting fn pointer. The reason has to do with external
52 // functions. If you have two crates that both bind the same C
53 // library, they may not use precisely the same types: for
54 // example, they will probably each declare their own structs,
55 // which are distinct types from LLVM's point of view (nominal
58 // Now, if those two crates are linked into an application, and
59 // they contain inlined code, you can wind up with a situation
60 // where both of those functions wind up being loaded into this
61 // application simultaneously. In that case, the same function
62 // (from LLVM's point of view) requires two types. But of course
63 // LLVM won't allow one function to have two types.
65 // What we currently do, therefore, is declare the function with
66 // one of the two types (whichever happens to come first) and then
67 // bitcast as needed when the function is referenced to make sure
68 // it has the type we expect.
70 // This can occur on either a crate-local or crate-external
71 // reference. It also occurs when testing libcore and in some
72 // other weird situations. Annoying.
73 if cx.val_ty(llfn) != llptrty {
74 debug!("get_fn: casting {:?} to {:?}", llfn, llptrty);
75 cx.const_ptrcast(llfn, llptrty)
77 debug!("get_fn: not casting pointer!");
81 let llfn = cx.declare_fn(&sym, &fn_abi);
82 debug!("get_fn: not casting pointer!");
84 attributes::from_fn_attrs(cx, llfn, instance, &fn_abi);
86 let instance_def_id = instance.def_id();
88 // Apply an appropriate linkage/visibility value to our item that we
91 // This is sort of subtle. Inside our codegen unit we started off
92 // compilation by predefining all our own `MonoItem` instances. That
93 // is, everything we're codegenning ourselves is already defined. That
94 // means that anything we're actually codegenning in this codegen unit
95 // will have hit the above branch in `get_declared_value`. As a result,
96 // we're guaranteed here that we're declaring a symbol that won't get
97 // defined, or in other words we're referencing a value from another
98 // codegen unit or even another crate.
100 // So because this is a foreign value we blanket apply an external
101 // linkage directive because it's coming from a different object file.
102 // The visibility here is where it gets tricky. This symbol could be
103 // referencing some foreign crate or foreign library (an `extern`
104 // block) in which case we want to leave the default visibility. We may
105 // also, though, have multiple codegen units. It could be a
106 // monomorphization, in which case its expected visibility depends on
107 // whether we are sharing generics or not. The important thing here is
108 // that the visibility we apply to the declaration is the same one that
109 // has been applied to the definition (wherever that definition may be).
111 llvm::LLVMRustSetLinkage(llfn, llvm::Linkage::ExternalLinkage);
113 let is_generic = instance.substs.non_erasable_generics().next().is_some();
116 // This is a monomorphization. Its expected visibility depends
117 // on whether we are in share-generics mode.
119 if cx.tcx.sess.opts.share_generics() {
120 // We are in share_generics mode.
122 if instance_def_id.is_local() {
123 // This is a definition from the current crate. If the
124 // definition is unreachable for downstream crates or
125 // the current crate does not re-export generics, the
126 // definition of the instance will have been declared
128 if cx.tcx.is_unreachable_local_definition(instance_def_id) ||
129 !cx.tcx.local_crate_exports_generics() {
130 llvm::LLVMRustSetVisibility(llfn, llvm::Visibility::Hidden);
133 // This is a monomorphization of a generic function
134 // defined in an upstream crate.
135 if cx.tcx.upstream_monomorphizations_for(instance_def_id)
136 .map(|set| set.contains_key(instance.substs))
138 // This is instantiated in another crate. It cannot
141 // This is a local instantiation of an upstream definition.
142 // If the current crate does not re-export it
143 // (because it is a C library or an executable), it
144 // will have been declared `hidden`.
145 if !cx.tcx.local_crate_exports_generics() {
146 llvm::LLVMRustSetVisibility(llfn, llvm::Visibility::Hidden);
151 // When not sharing generics, all instances are in the same
152 // crate and have hidden visibility
153 llvm::LLVMRustSetVisibility(llfn, llvm::Visibility::Hidden);
156 // This is a non-generic function
157 if cx.tcx.is_codegened_item(instance_def_id) {
158 // This is a function that is instantiated in the local crate
160 if instance_def_id.is_local() {
161 // This is function that is defined in the local crate.
162 // If it is not reachable, it is hidden.
163 if !cx.tcx.is_reachable_non_generic(instance_def_id) {
164 llvm::LLVMRustSetVisibility(llfn, llvm::Visibility::Hidden);
167 // This is a function from an upstream crate that has
168 // been instantiated here. These are always hidden.
169 llvm::LLVMRustSetVisibility(llfn, llvm::Visibility::Hidden);
175 if cx.use_dll_storage_attrs &&
176 tcx.is_dllimport_foreign_item(instance_def_id)
179 llvm::LLVMSetDLLStorageClass(llfn, llvm::DLLStorageClass::DllImport);
186 cx.instances.borrow_mut().insert(instance, llfn);