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 attributes::from_fn_attrs(cx, llfn, instance, &fn_abi);
85 let instance_def_id = instance.def_id();
87 // Apply an appropriate linkage/visibility value to our item that we
90 // This is sort of subtle. Inside our codegen unit we started off
91 // compilation by predefining all our own `MonoItem` instances. That
92 // is, everything we're codegenning ourselves is already defined. That
93 // means that anything we're actually codegenning in this codegen unit
94 // will have hit the above branch in `get_declared_value`. As a result,
95 // we're guaranteed here that we're declaring a symbol that won't get
96 // defined, or in other words we're referencing a value from another
97 // codegen unit or even another crate.
99 // So because this is a foreign value we blanket apply an external
100 // linkage directive because it's coming from a different object file.
101 // The visibility here is where it gets tricky. This symbol could be
102 // referencing some foreign crate or foreign library (an `extern`
103 // block) in which case we want to leave the default visibility. We may
104 // also, though, have multiple codegen units. It could be a
105 // monomorphization, in which case its expected visibility depends on
106 // whether we are sharing generics or not. The important thing here is
107 // that the visibility we apply to the declaration is the same one that
108 // has been applied to the definition (wherever that definition may be).
110 llvm::LLVMRustSetLinkage(llfn, llvm::Linkage::ExternalLinkage);
112 let is_generic = instance.substs.non_erasable_generics().next().is_some();
115 // This is a monomorphization. Its expected visibility depends
116 // on whether we are in share-generics mode.
118 if cx.tcx.sess.opts.share_generics() {
119 // We are in share_generics mode.
121 if instance_def_id.is_local() {
122 // This is a definition from the current crate. If the
123 // definition is unreachable for downstream crates or
124 // the current crate does not re-export generics, the
125 // definition of the instance will have been declared
127 if cx.tcx.is_unreachable_local_definition(instance_def_id) ||
128 !cx.tcx.local_crate_exports_generics() {
129 llvm::LLVMRustSetVisibility(llfn, llvm::Visibility::Hidden);
132 // This is a monomorphization of a generic function
133 // defined in an upstream crate.
134 if cx.tcx.upstream_monomorphizations_for(instance_def_id)
135 .map(|set| set.contains_key(instance.substs))
137 // This is instantiated in another crate. It cannot
140 // This is a local instantiation of an upstream definition.
141 // If the current crate does not re-export it
142 // (because it is a C library or an executable), it
143 // will have been declared `hidden`.
144 if !cx.tcx.local_crate_exports_generics() {
145 llvm::LLVMRustSetVisibility(llfn, llvm::Visibility::Hidden);
150 // When not sharing generics, all instances are in the same
151 // crate and have hidden visibility
152 llvm::LLVMRustSetVisibility(llfn, llvm::Visibility::Hidden);
155 // This is a non-generic function
156 if cx.tcx.is_codegened_item(instance_def_id) {
157 // This is a function that is instantiated in the local crate
159 if instance_def_id.is_local() {
160 // This is function that is defined in the local crate.
161 // If it is not reachable, it is hidden.
162 if !cx.tcx.is_reachable_non_generic(instance_def_id) {
163 llvm::LLVMRustSetVisibility(llfn, llvm::Visibility::Hidden);
166 // This is a function from an upstream crate that has
167 // been instantiated here. These are always hidden.
168 llvm::LLVMRustSetVisibility(llfn, llvm::Visibility::Hidden);
174 if cx.use_dll_storage_attrs &&
175 tcx.is_dllimport_foreign_item(instance_def_id)
178 llvm::LLVMSetDLLStorageClass(llfn, llvm::DLLStorageClass::DllImport);
185 cx.instances.borrow_mut().insert(instance, llfn);