rust/src/librustc_trans/attributes.rs

// Copyright 2012-2015 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.
//! Set and unset common attributes on LLVM values.

use std::ffi::{CStr, CString};

use rustc::hir::TransFnAttrFlags;
use rustc::hir::def_id::{DefId, LOCAL_CRATE};
use rustc::session::config::Sanitizer;
use rustc::ty::maps::Providers;
use rustc_data_structures::sync::Lrc;

use llvm::{self, Attribute, ValueRef};
use llvm::AttributePlace::Function;
use llvm_util;
pub use syntax::attr::{self, InlineAttr};
use context::CodegenCx;

/// Mark LLVM function to use provided inline heuristic.
#[inline]
pub fn inline(val: ValueRef, inline: InlineAttr) {
    use self::InlineAttr::*;
    match inline {
        Hint   => Attribute::InlineHint.apply_llfn(Function, val),
        Always => Attribute::AlwaysInline.apply_llfn(Function, val),
        Never  => Attribute::NoInline.apply_llfn(Function, val),
        None   => {
            Attribute::InlineHint.unapply_llfn(Function, val);
            Attribute::AlwaysInline.unapply_llfn(Function, val);
            Attribute::NoInline.unapply_llfn(Function, val);
        },
    };
}

/// Tell LLVM to emit or not emit the information necessary to unwind the stack for the function.
#[inline]
pub fn emit_uwtable(val: ValueRef, emit: bool) {
    Attribute::UWTable.toggle_llfn(Function, val, emit);
}

/// Tell LLVM whether the function can or cannot unwind.
#[inline]
pub fn unwind(val: ValueRef, can_unwind: bool) {
    Attribute::NoUnwind.toggle_llfn(Function, val, !can_unwind);
}

/// Tell LLVM whether it should optimize function for size.
#[inline]
#[allow(dead_code)] // possibly useful function
pub fn set_optimize_for_size(val: ValueRef, optimize: bool) {
    Attribute::OptimizeForSize.toggle_llfn(Function, val, optimize);
}

/// Tell LLVM if this function should be 'naked', i.e. skip the epilogue and prologue.
#[inline]
pub fn naked(val: ValueRef, is_naked: bool) {
    Attribute::Naked.toggle_llfn(Function, val, is_naked);
}

pub fn set_frame_pointer_elimination(cx: &CodegenCx, llfn: ValueRef) {
    // FIXME: #11906: Omitting frame pointers breaks retrieving the value of a
    // parameter.
    if cx.sess().must_not_eliminate_frame_pointers() {
        llvm::AddFunctionAttrStringValue(
            llfn, llvm::AttributePlace::Function,
            cstr("no-frame-pointer-elim\0"), cstr("true\0"));
    }
}

pub fn set_probestack(cx: &CodegenCx, llfn: ValueRef) {
    // Only use stack probes if the target specification indicates that we
    // should be using stack probes
    if !cx.sess().target.target.options.stack_probes {
        return
    }

    // Currently stack probes seem somewhat incompatible with the address
    // sanitizer. With asan we're already protected from stack overflow anyway
    // so we don't really need stack probes regardless.
    match cx.sess().opts.debugging_opts.sanitizer {
        Some(Sanitizer::Address) => return,
        _ => {}
    }

    // Flag our internal `__rust_probestack` function as the stack probe symbol.
    // This is defined in the `compiler-builtins` crate for each architecture.
    llvm::AddFunctionAttrStringValue(
        llfn, llvm::AttributePlace::Function,
        cstr("probe-stack\0"), cstr("__rust_probestack\0"));
}

/// Composite function which sets LLVM attributes for function depending on its AST (#[attribute])
/// attributes.
pub fn from_fn_attrs(cx: &CodegenCx, llfn: ValueRef, id: DefId) {
    let trans_fn_attrs = cx.tcx.trans_fn_attrs(id);

    inline(llfn, trans_fn_attrs.inline);

    set_frame_pointer_elimination(cx, llfn);
    set_probestack(cx, llfn);

    if trans_fn_attrs.flags.contains(TransFnAttrFlags::COLD) {
        Attribute::Cold.apply_llfn(Function, llfn);
    }
    if trans_fn_attrs.flags.contains(TransFnAttrFlags::NAKED) {
        naked(llfn, true);
    }
    if trans_fn_attrs.flags.contains(TransFnAttrFlags::ALLOCATOR) {
        Attribute::NoAlias.apply_llfn(
            llvm::AttributePlace::ReturnValue, llfn);
    }
    if trans_fn_attrs.flags.contains(TransFnAttrFlags::UNWIND) {
        unwind(llfn, true);
    }
    if trans_fn_attrs.flags.contains(TransFnAttrFlags::RUSTC_ALLOCATOR_NOUNWIND) {
        unwind(llfn, false);
    }

    let features =
        trans_fn_attrs.target_features
        .iter()
        .map(|f| {
            let feature = &*f.as_str();
            format!("+{}", llvm_util::to_llvm_feature(cx.tcx.sess, feature))
        })
        .collect::<Vec<String>>()
        .join(",");

    if !features.is_empty() {
        let val = CString::new(features).unwrap();
        llvm::AddFunctionAttrStringValue(
            llfn, llvm::AttributePlace::Function,
            cstr("target-features\0"), &val);
    }
}

fn cstr(s: &'static str) -> &CStr {
    CStr::from_bytes_with_nul(s.as_bytes()).expect("null-terminated string")
}

pub fn provide(providers: &mut Providers) {
    providers.target_features_whitelist = |tcx, cnum| {
        assert_eq!(cnum, LOCAL_CRATE);
        if tcx.sess.opts.actually_rustdoc {
            // rustdoc needs to be able to document functions that use all the features, so
            // whitelist them all
            Lrc::new(llvm_util::all_known_features()
                .map(|c| c.to_string())
                .collect())
        } else {
            Lrc::new(llvm_util::target_feature_whitelist(tcx.sess)
                .iter()
                .map(|c| c.to_string())
                .collect())
        }
    };
}