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};
9 use crate::context::CodegenCx;
11 use crate::value::Value;
13 use rustc_codegen_ssa::traits::*;
15 use rustc::ty::layout::{FnAbiExt, HasTyCtxt};
16 use rustc::ty::{Instance, TypeFoldable};
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
25 pub fn get_fn(cx: &CodegenCx<'ll, 'tcx>, instance: Instance<'tcx>) -> &'ll Value {
28 debug!("get_fn(instance={:?})", instance);
30 assert!(!instance.substs.needs_infer());
31 assert!(!instance.substs.has_escaping_bound_vars());
32 assert!(!instance.substs.has_param_types());
34 if let Some(&llfn) = cx.instances.borrow().get(&instance) {
38 let sym = tcx.symbol_name(instance).name.as_str();
39 debug!("get_fn({:?}: {:?}) => {}", instance, instance.monomorphic_ty(cx.tcx()), sym);
41 let fn_abi = FnAbi::of_instance(cx, instance, &[]);
43 let llfn = if let Some(llfn) = cx.get_declared_value(&sym) {
44 // Create a fn pointer with the new signature.
45 let llptrty = fn_abi.ptr_to_llvm_type(cx);
47 // This is subtle and surprising, but sometimes we have to bitcast
48 // the resulting fn pointer. The reason has to do with external
49 // functions. If you have two crates that both bind the same C
50 // library, they may not use precisely the same types: for
51 // example, they will probably each declare their own structs,
52 // which are distinct types from LLVM's point of view (nominal
55 // Now, if those two crates are linked into an application, and
56 // they contain inlined code, you can wind up with a situation
57 // where both of those functions wind up being loaded into this
58 // application simultaneously. In that case, the same function
59 // (from LLVM's point of view) requires two types. But of course
60 // LLVM won't allow one function to have two types.
62 // What we currently do, therefore, is declare the function with
63 // one of the two types (whichever happens to come first) and then
64 // bitcast as needed when the function is referenced to make sure
65 // it has the type we expect.
67 // This can occur on either a crate-local or crate-external
68 // reference. It also occurs when testing libcore and in some
69 // other weird situations. Annoying.
70 if cx.val_ty(llfn) != llptrty {
71 debug!("get_fn: casting {:?} to {:?}", llfn, llptrty);
72 cx.const_ptrcast(llfn, llptrty)
74 debug!("get_fn: not casting pointer!");
78 let llfn = cx.declare_fn(&sym, &fn_abi);
79 debug!("get_fn: not casting pointer!");
81 attributes::from_fn_attrs(cx, llfn, instance, &fn_abi);
83 let instance_def_id = instance.def_id();
85 // Apply an appropriate linkage/visibility value to our item that we
88 // This is sort of subtle. Inside our codegen unit we started off
89 // compilation by predefining all our own `MonoItem` instances. That
90 // is, everything we're codegenning ourselves is already defined. That
91 // means that anything we're actually codegenning in this codegen unit
92 // will have hit the above branch in `get_declared_value`. As a result,
93 // we're guaranteed here that we're declaring a symbol that won't get
94 // defined, or in other words we're referencing a value from another
95 // codegen unit or even another crate.
97 // So because this is a foreign value we blanket apply an external
98 // linkage directive because it's coming from a different object file.
99 // The visibility here is where it gets tricky. This symbol could be
100 // referencing some foreign crate or foreign library (an `extern`
101 // block) in which case we want to leave the default visibility. We may
102 // also, though, have multiple codegen units. It could be a
103 // monomorphization, in which case its expected visibility depends on
104 // whether we are sharing generics or not. The important thing here is
105 // that the visibility we apply to the declaration is the same one that
106 // has been applied to the definition (wherever that definition may be).
108 llvm::LLVMRustSetLinkage(llfn, llvm::Linkage::ExternalLinkage);
110 let is_generic = instance.substs.non_erasable_generics().next().is_some();
113 // This is a monomorphization. Its expected visibility depends
114 // on whether we are in share-generics mode.
116 if cx.tcx.sess.opts.share_generics() {
117 // We are in share_generics mode.
119 if instance_def_id.is_local() {
120 // This is a definition from the current crate. If the
121 // definition is unreachable for downstream crates or
122 // the current crate does not re-export generics, the
123 // definition of the instance will have been declared
125 if cx.tcx.is_unreachable_local_definition(instance_def_id)
126 || !cx.tcx.local_crate_exports_generics()
128 llvm::LLVMRustSetVisibility(llfn, llvm::Visibility::Hidden);
131 // This is a monomorphization of a generic function
132 // defined in an upstream crate.
133 if instance.upstream_monomorphization(tcx).is_some() {
134 // This is instantiated in another crate. It cannot
137 // This is a local instantiation of an upstream definition.
138 // If the current crate does not re-export it
139 // (because it is a C library or an executable), it
140 // will have been declared `hidden`.
141 if !cx.tcx.local_crate_exports_generics() {
142 llvm::LLVMRustSetVisibility(llfn, llvm::Visibility::Hidden);
147 // When not sharing generics, all instances are in the same
148 // crate and have hidden visibility
149 llvm::LLVMRustSetVisibility(llfn, llvm::Visibility::Hidden);
152 // This is a non-generic function
153 if cx.tcx.is_codegened_item(instance_def_id) {
154 // This is a function that is instantiated in the local crate
156 if instance_def_id.is_local() {
157 // This is function that is defined in the local crate.
158 // If it is not reachable, it is hidden.
159 if !cx.tcx.is_reachable_non_generic(instance_def_id) {
160 llvm::LLVMRustSetVisibility(llfn, llvm::Visibility::Hidden);
163 // This is a function from an upstream crate that has
164 // been instantiated here. These are always hidden.
165 llvm::LLVMRustSetVisibility(llfn, llvm::Visibility::Hidden);
171 if cx.use_dll_storage_attrs && tcx.is_dllimport_foreign_item(instance_def_id) {
173 llvm::LLVMSetDLLStorageClass(llfn, llvm::DLLStorageClass::DllImport);
180 cx.instances.borrow_mut().insert(instance, llfn);