compiler/rustc_codegen_llvm/src/declare.rs

   1 //! Declare various LLVM values.
   2 //!
   3 //! Prefer using functions and methods from this module rather than calling LLVM
   4 //! functions directly. These functions do some additional work to ensure we do
   5 //! the right thing given the preconceptions of codegen.
   6 //!
   7 //! Some useful guidelines:
   8 //!
   9 //! * Use declare_* family of methods if you are declaring, but are not
  10 //!   interested in defining the Value they return.
  11 //! * Use define_* family of methods when you might be defining the Value.
  12 //! * When in doubt, define.
  13
  14 use crate::abi::{FnAbi, FnAbiLlvmExt};
  15 use crate::attributes;
  16 use crate::context::CodegenCx;
  17 use crate::llvm;
  18 use crate::llvm::AttributePlace::Function;
  19 use crate::type_::Type;
  20 use crate::value::Value;
  21 use rustc_codegen_ssa::traits::*;
  22 use rustc_middle::ty::Ty;
  23 use tracing::debug;
  24
  25 /// Declare a function.
  26 ///
  27 /// If there’s a value with the same name already declared, the function will
  28 /// update the declaration and return existing Value instead.
  29 fn declare_raw_fn(
  30     cx: &CodegenCx<'ll, '_>,
  31     name: &str,
  32     callconv: llvm::CallConv,
  33     ty: &'ll Type,
  34 ) -> &'ll Value {
  35     debug!("declare_raw_fn(name={:?}, ty={:?})", name, ty);
  36     let llfn = unsafe {
  37         llvm::LLVMRustGetOrInsertFunction(cx.llmod, name.as_ptr().cast(), name.len(), ty)
  38     };
  39
  40     llvm::SetFunctionCallConv(llfn, callconv);
  41     // Function addresses in Rust are never significant, allowing functions to
  42     // be merged.
  43     llvm::SetUnnamedAddress(llfn, llvm::UnnamedAddr::Global);
  44
  45     if cx.tcx.sess.opts.cg.no_redzone.unwrap_or(cx.tcx.sess.target.disable_redzone) {
  46         llvm::Attribute::NoRedZone.apply_llfn(Function, llfn);
  47     }
  48
  49     attributes::default_optimisation_attrs(cx.tcx.sess, llfn);
  50     attributes::non_lazy_bind(cx.sess(), llfn);
  51     llfn
  52 }
  53
  54 impl CodegenCx<'ll, 'tcx> {
  55     /// Declare a global value.
  56     ///
  57     /// If there’s a value with the same name already declared, the function will
  58     /// return its Value instead.
  59     pub fn declare_global(&self, name: &str, ty: &'ll Type) -> &'ll Value {
  60         debug!("declare_global(name={:?})", name);
  61         unsafe { llvm::LLVMRustGetOrInsertGlobal(self.llmod, name.as_ptr().cast(), name.len(), ty) }
  62     }
  63
  64     /// Declare a C ABI function.
  65     ///
  66     /// Only use this for foreign function ABIs and glue. For Rust functions use
  67     /// `declare_fn` instead.
  68     ///
  69     /// If there’s a value with the same name already declared, the function will
  70     /// update the declaration and return existing Value instead.
  71     pub fn declare_cfn(&self, name: &str, fn_type: &'ll Type) -> &'ll Value {
  72         declare_raw_fn(self, name, llvm::CCallConv, fn_type)
  73     }
  74
  75     /// Declare a Rust function.
  76     ///
  77     /// If there’s a value with the same name already declared, the function will
  78     /// update the declaration and return existing Value instead.
  79     pub fn declare_fn(&self, name: &str, fn_abi: &FnAbi<'tcx, Ty<'tcx>>) -> &'ll Value {
  80         debug!("declare_rust_fn(name={:?}, fn_abi={:?})", name, fn_abi);
  81
  82         let llfn = declare_raw_fn(self, name, fn_abi.llvm_cconv(), fn_abi.llvm_type(self));
  83         fn_abi.apply_attrs_llfn(self, llfn);
  84         llfn
  85     }
  86
  87     /// Declare a global with an intention to define it.
  88     ///
  89     /// Use this function when you intend to define a global. This function will
  90     /// return `None` if the name already has a definition associated with it. In that
  91     /// case an error should be reported to the user, because it usually happens due
  92     /// to user’s fault (e.g., misuse of `#[no_mangle]` or `#[export_name]` attributes).
  93     pub fn define_global(&self, name: &str, ty: &'ll Type) -> Option<&'ll Value> {
  94         if self.get_defined_value(name).is_some() {
  95             None
  96         } else {
  97             Some(self.declare_global(name, ty))
  98         }
  99     }
 100
 101     /// Declare a private global
 102     ///
 103     /// Use this function when you intend to define a global without a name.
 104     pub fn define_private_global(&self, ty: &'ll Type) -> &'ll Value {
 105         unsafe { llvm::LLVMRustInsertPrivateGlobal(self.llmod, ty) }
 106     }
 107
 108     /// Gets declared value by name.
 109     pub fn get_declared_value(&self, name: &str) -> Option<&'ll Value> {
 110         debug!("get_declared_value(name={:?})", name);
 111         unsafe { llvm::LLVMRustGetNamedValue(self.llmod, name.as_ptr().cast(), name.len()) }
 112     }
 113
 114     /// Gets defined or externally defined (AvailableExternally linkage) value by
 115     /// name.
 116     pub fn get_defined_value(&self, name: &str) -> Option<&'ll Value> {
 117         self.get_declared_value(name).and_then(|val| {
 118             let declaration = unsafe { llvm::LLVMIsDeclaration(val) != 0 };
 119             if !declaration { Some(val) } else { None }
 120         })
 121     }
 122 }