rust/src/librustc_codegen_llvm/declare.rs

//! Declare various LLVM values.
//!
//! Prefer using functions and methods from this module rather than calling LLVM
//! functions directly. These functions do some additional work to ensure we do
//! the right thing given the preconceptions of codegen.
//!
//! Some useful guidelines:
//!
//! * Use declare_* family of methods if you are declaring, but are not
//!   interested in defining the Value they return.
//! * Use define_* family of methods when you might be defining the Value.
//! * When in doubt, define.

use crate::llvm;
use crate::llvm::AttributePlace::Function;
use crate::abi::{FnType, FnTypeLlvmExt};
use crate::attributes;
use crate::context::CodegenCx;
use crate::type_::Type;
use crate::value::Value;
use rustc::ty::{self, PolyFnSig};
use rustc::ty::layout::{FnTypeExt, LayoutOf};
use rustc::session::config::Sanitizer;
use rustc_data_structures::small_c_str::SmallCStr;
use rustc_codegen_ssa::traits::*;

/// Declare a function.
///
/// If there’s a value with the same name already declared, the function will
/// update the declaration and return existing Value instead.
fn declare_raw_fn(
    cx: &CodegenCx<'ll, '_>,
    name: &str,
    callconv: llvm::CallConv,
    ty: &'ll Type,
) -> &'ll Value {
    debug!("declare_raw_fn(name={:?}, ty={:?})", name, ty);
    let namebuf = SmallCStr::new(name);
    let llfn = unsafe {
        llvm::LLVMRustGetOrInsertFunction(cx.llmod, namebuf.as_ptr(), ty)
    };

    llvm::SetFunctionCallConv(llfn, callconv);
    // Function addresses in Rust are never significant, allowing functions to
    // be merged.
    llvm::SetUnnamedAddr(llfn, true);

    if cx.tcx.sess.opts.cg.no_redzone
        .unwrap_or(cx.tcx.sess.target.target.options.disable_redzone) {
        llvm::Attribute::NoRedZone.apply_llfn(Function, llfn);
    }

    if let Some(ref sanitizer) = cx.tcx.sess.opts.debugging_opts.sanitizer {
        match *sanitizer {
            Sanitizer::Address => {
                llvm::Attribute::SanitizeAddress.apply_llfn(Function, llfn);
            },
            Sanitizer::Memory => {
                llvm::Attribute::SanitizeMemory.apply_llfn(Function, llfn);
            },
            Sanitizer::Thread => {
                llvm::Attribute::SanitizeThread.apply_llfn(Function, llfn);
            },
            _ => {}
        }
    }

    attributes::default_optimisation_attrs(cx.tcx.sess, llfn);
    attributes::non_lazy_bind(cx.sess(), llfn);
    llfn
}

impl DeclareMethods<'tcx> for CodegenCx<'ll, 'tcx> {

    fn declare_global(
        &self,
        name: &str, ty: &'ll Type
    ) -> &'ll Value {
        debug!("declare_global(name={:?})", name);
        let namebuf = SmallCStr::new(name);
        unsafe {
            llvm::LLVMRustGetOrInsertGlobal(self.llmod, namebuf.as_ptr(), ty)
        }
    }

    fn declare_cfn(
        &self,
        name: &str,
        fn_type: &'ll Type
    ) -> &'ll Value {
        declare_raw_fn(self, name, llvm::CCallConv, fn_type)
    }

    fn declare_fn(
        &self,
        name: &str,
        sig: PolyFnSig<'tcx>,
    ) -> &'ll Value {
        debug!("declare_rust_fn(name={:?}, sig={:?})", name, sig);
        let sig = self.tcx.normalize_erasing_late_bound_regions(ty::ParamEnv::reveal_all(), &sig);
        debug!("declare_rust_fn (after region erasure) sig={:?}", sig);

        let fty = FnType::new(self, sig, &[]);
        let llfn = declare_raw_fn(self, name, fty.llvm_cconv(), fty.llvm_type(self));

        if self.layout_of(sig.output()).abi.is_uninhabited() {
            llvm::Attribute::NoReturn.apply_llfn(Function, llfn);
        }

        fty.apply_attrs_llfn(self, llfn);

        llfn
    }

    fn define_global(
        &self,
        name: &str,
        ty: &'ll Type
    ) -> Option<&'ll Value> {
        if self.get_defined_value(name).is_some() {
            None
        } else {
            Some(self.declare_global(name, ty))
        }
    }

    fn define_private_global(&self, ty: &'ll Type) -> &'ll Value {
        unsafe {
            llvm::LLVMRustInsertPrivateGlobal(self.llmod, ty)
        }
    }

    fn define_fn(
        &self,
        name: &str,
        fn_sig: PolyFnSig<'tcx>,
    ) -> &'ll Value {
        if self.get_defined_value(name).is_some() {
            self.sess().fatal(&format!("symbol `{}` already defined", name))
        } else {
            self.declare_fn(name, fn_sig)
        }
    }

    fn define_internal_fn(
        &self,
        name: &str,
        fn_sig: PolyFnSig<'tcx>,
    ) -> &'ll Value {
        let llfn = self.define_fn(name, fn_sig);
        unsafe { llvm::LLVMRustSetLinkage(llfn, llvm::Linkage::InternalLinkage) };
        llfn
    }

    fn get_declared_value(&self, name: &str) -> Option<&'ll Value> {
        debug!("get_declared_value(name={:?})", name);
        let namebuf = SmallCStr::new(name);
        unsafe { llvm::LLVMRustGetNamedValue(self.llmod, namebuf.as_ptr()) }
    }

    fn get_defined_value(&self, name: &str) -> Option<&'ll Value> {
        self.get_declared_value(name).and_then(|val|{
            let declaration = unsafe {
                llvm::LLVMIsDeclaration(val) != 0
            };
            if !declaration {
                Some(val)
            } else {
                None
            }
        })
    }
}