193 lines
8.5 KiB
Rust
193 lines
8.5 KiB
Rust
//! Handles codegen of callees as well as other call-related
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//! things. Callees are a superset of normal rust values and sometimes
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//! have different representations. In particular, top-level fn items
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//! and methods are represented as just a fn ptr and not a full
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//! closure.
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use crate::attributes;
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use crate::llvm;
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use crate::monomorphize::Instance;
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use crate::context::CodegenCx;
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use crate::value::Value;
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use rustc_codegen_ssa::traits::*;
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use rustc::ty::TypeFoldable;
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use rustc::ty::layout::{LayoutOf, HasTyCtxt};
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/// Codegens a reference to a fn/method item, monomorphizing and
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/// inlining as it goes.
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///
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/// # Parameters
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///
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/// - `cx`: the crate context
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/// - `instance`: the instance to be instantiated
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pub fn get_fn(
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cx: &CodegenCx<'ll, 'tcx>,
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instance: Instance<'tcx>,
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) -> &'ll Value {
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let tcx = cx.tcx();
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debug!("get_fn(instance={:?})", instance);
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assert!(!instance.substs.needs_infer());
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assert!(!instance.substs.has_escaping_bound_vars());
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assert!(!instance.substs.has_param_types());
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let sig = instance.fn_sig(cx.tcx());
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if let Some(&llfn) = cx.instances().borrow().get(&instance) {
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return llfn;
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}
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let sym = tcx.symbol_name(instance).as_str();
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debug!("get_fn({:?}: {:?}) => {}", instance, sig, sym);
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// Create a fn pointer with the substituted signature.
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let fn_ptr_ty = tcx.mk_fn_ptr(sig);
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let llptrty = cx.backend_type(cx.layout_of(fn_ptr_ty));
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let llfn = if let Some(llfn) = cx.get_declared_value(&sym) {
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// This is subtle and surprising, but sometimes we have to bitcast
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// the resulting fn pointer. The reason has to do with external
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// functions. If you have two crates that both bind the same C
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// library, they may not use precisely the same types: for
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// example, they will probably each declare their own structs,
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// which are distinct types from LLVM's point of view (nominal
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// types).
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//
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// Now, if those two crates are linked into an application, and
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// they contain inlined code, you can wind up with a situation
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// where both of those functions wind up being loaded into this
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// application simultaneously. In that case, the same function
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// (from LLVM's point of view) requires two types. But of course
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// LLVM won't allow one function to have two types.
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//
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// What we currently do, therefore, is declare the function with
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// one of the two types (whichever happens to come first) and then
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// bitcast as needed when the function is referenced to make sure
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// it has the type we expect.
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//
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// This can occur on either a crate-local or crate-external
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// reference. It also occurs when testing libcore and in some
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// other weird situations. Annoying.
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if cx.val_ty(llfn) != llptrty {
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debug!("get_fn: casting {:?} to {:?}", llfn, llptrty);
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cx.const_ptrcast(llfn, llptrty)
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} else {
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debug!("get_fn: not casting pointer!");
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llfn
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}
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} else {
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let llfn = cx.declare_fn(&sym, sig);
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assert_eq!(cx.val_ty(llfn), llptrty);
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debug!("get_fn: not casting pointer!");
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if instance.def.is_inline(tcx) {
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attributes::inline(cx, llfn, attributes::InlineAttr::Hint);
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}
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attributes::from_fn_attrs(cx, llfn, Some(instance.def.def_id()), sig);
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let instance_def_id = instance.def_id();
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// Apply an appropriate linkage/visibility value to our item that we
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// just declared.
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//
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// This is sort of subtle. Inside our codegen unit we started off
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// compilation by predefining all our own `MonoItem` instances. That
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// is, everything we're codegenning ourselves is already defined. That
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// means that anything we're actually codegenning in this codegen unit
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// will have hit the above branch in `get_declared_value`. As a result,
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// we're guaranteed here that we're declaring a symbol that won't get
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// defined, or in other words we're referencing a value from another
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// codegen unit or even another crate.
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//
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// So because this is a foreign value we blanket apply an external
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// linkage directive because it's coming from a different object file.
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// The visibility here is where it gets tricky. This symbol could be
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// referencing some foreign crate or foreign library (an `extern`
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// block) in which case we want to leave the default visibility. We may
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// also, though, have multiple codegen units. It could be a
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// monomorphization, in which case its expected visibility depends on
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// whether we are sharing generics or not. The important thing here is
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// that the visibility we apply to the declaration is the same one that
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// has been applied to the definition (wherever that definition may be).
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unsafe {
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llvm::LLVMRustSetLinkage(llfn, llvm::Linkage::ExternalLinkage);
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let is_generic = instance.substs.non_erasable_generics().next().is_some();
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if is_generic {
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// This is a monomorphization. Its expected visibility depends
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// on whether we are in share-generics mode.
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if cx.tcx.sess.opts.share_generics() {
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// We are in share_generics mode.
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if instance_def_id.is_local() {
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// This is a definition from the current crate. If the
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// definition is unreachable for downstream crates or
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// the current crate does not re-export generics, the
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// definition of the instance will have been declared
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// as `hidden`.
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if cx.tcx.is_unreachable_local_definition(instance_def_id) ||
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!cx.tcx.local_crate_exports_generics() {
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llvm::LLVMRustSetVisibility(llfn, llvm::Visibility::Hidden);
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}
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} else {
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// This is a monomorphization of a generic function
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// defined in an upstream crate.
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if cx.tcx.upstream_monomorphizations_for(instance_def_id)
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.map(|set| set.contains_key(instance.substs))
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.unwrap_or(false) {
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// This is instantiated in another crate. It cannot
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// be `hidden`.
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} else {
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// This is a local instantiation of an upstream definition.
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// If the current crate does not re-export it
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// (because it is a C library or an executable), it
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// will have been declared `hidden`.
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if !cx.tcx.local_crate_exports_generics() {
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llvm::LLVMRustSetVisibility(llfn, llvm::Visibility::Hidden);
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}
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}
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}
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} else {
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// When not sharing generics, all instances are in the same
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// crate and have hidden visibility
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llvm::LLVMRustSetVisibility(llfn, llvm::Visibility::Hidden);
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}
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} else {
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// This is a non-generic function
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if cx.tcx.is_codegened_item(instance_def_id) {
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// This is a function that is instantiated in the local crate
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if instance_def_id.is_local() {
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// This is function that is defined in the local crate.
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// If it is not reachable, it is hidden.
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if !cx.tcx.is_reachable_non_generic(instance_def_id) {
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llvm::LLVMRustSetVisibility(llfn, llvm::Visibility::Hidden);
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}
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} else {
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// This is a function from an upstream crate that has
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// been instantiated here. These are always hidden.
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llvm::LLVMRustSetVisibility(llfn, llvm::Visibility::Hidden);
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}
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}
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}
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}
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if cx.use_dll_storage_attrs &&
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tcx.is_dllimport_foreign_item(instance_def_id)
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{
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unsafe {
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llvm::LLVMSetDLLStorageClass(llfn, llvm::DLLStorageClass::DllImport);
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}
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}
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llfn
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};
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cx.instances.borrow_mut().insert(instance, llfn);
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llfn
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}
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