rust/src/constant.rs

use cranelift_module::*;
use crate::prelude::*;
use rustc::mir::interpret::{read_target_uint, AllocId, AllocType, ConstValue, GlobalId};
use rustc::ty::Const;
use rustc_mir::interpret::{CompileTimeEvaluator, Memory};
use syntax::ast::Mutability as AstMutability;

#[derive(Default)]
pub struct ConstantCx {
    todo: HashSet<TodoItem>,
    done: HashSet<DataId>,
}

#[derive(Copy, Clone, Debug, Eq, PartialEq, Hash)]
enum TodoItem {
    Alloc(AllocId),
    Static(DefId),
}

impl ConstantCx {
    pub fn finalize<'a, 'tcx: 'a, B: Backend>(
        mut self,
        tcx: TyCtxt<'a, 'tcx, 'tcx>,
        module: &mut Module<B>,
    ) {
        //println!("todo {:?}", self.todo);
        define_all_allocs(tcx, module, &mut self);
        //println!("done {:?}", self.done);
        for data_id in self.done.drain() {
            module.finalize_data(data_id);
        }
    }
}

pub fn codegen_static<'a, 'tcx: 'a>(ccx: &mut ConstantCx, def_id: DefId) {
    ccx.todo.insert(TodoItem::Static(def_id));
}

pub fn codegen_static_ref<'a, 'tcx: 'a>(
    fx: &mut FunctionCx<'a, 'tcx, impl Backend>,
    static_: &Static<'tcx>,
) -> CPlace<'tcx> {
    let data_id = data_id_for_static(fx.tcx, fx.module, static_.def_id);
    cplace_for_dataid(fx, static_.ty, data_id)
}

pub fn trans_promoted<'a, 'tcx: 'a>(
    fx: &mut FunctionCx<'a, 'tcx, impl Backend>,
    promoted: Promoted,
) -> CPlace<'tcx> {
    let const_ = fx
        .tcx
        .const_eval(ParamEnv::reveal_all().and(GlobalId {
            instance: fx.instance,
            promoted: Some(promoted),
        })).unwrap();

    let const_ = force_eval_const(fx, const_);
    trans_const_place(fx, const_)
}

pub fn trans_constant<'a, 'tcx: 'a>(
    fx: &mut FunctionCx<'a, 'tcx, impl Backend>,
    constant: &Constant<'tcx>,
) -> CValue<'tcx> {
    let const_ = fx.monomorphize(&constant.literal);
    let const_ = force_eval_const(fx, const_);
    trans_const_value(fx, const_)
}

fn force_eval_const<'a, 'tcx: 'a>(
    fx: &FunctionCx<'a, 'tcx, impl Backend>,
    const_: &'tcx Const<'tcx>,
) -> &'tcx Const<'tcx> {
    match const_.val {
        ConstValue::Unevaluated(def_id, ref substs) => {
            let param_env = ParamEnv::reveal_all();
            let instance = Instance::resolve(fx.tcx, param_env, def_id, substs).unwrap();
            let cid = GlobalId {
                instance,
                promoted: None,
            };
            fx.tcx.const_eval(param_env.and(cid)).unwrap()
        }
        _ => const_,
    }
}

fn trans_const_value<'a, 'tcx: 'a>(
    fx: &mut FunctionCx<'a, 'tcx, impl Backend>,
    const_: &'tcx Const<'tcx>,
) -> CValue<'tcx> {
    let ty = fx.monomorphize(&const_.ty);
    let layout = fx.layout_of(ty);
    match ty.sty {
        TypeVariants::TyBool => {
            let bits = const_.val.to_bits(layout.size).unwrap();
            CValue::const_val(fx, ty, bits as u64 as i64)
        }
        TypeVariants::TyUint(_) => {
            let bits = const_.val.to_bits(layout.size).unwrap();
            CValue::const_val(fx, ty, bits as u64 as i64)
        }
        TypeVariants::TyInt(_) => {
            let bits = const_.val.to_bits(layout.size).unwrap();
            CValue::const_val(fx, ty, bits as i128 as i64)
        }
        TypeVariants::TyFnDef(def_id, substs) => {
            let func_ref = fx.get_function_ref(
                Instance::resolve(fx.tcx, ParamEnv::reveal_all(), def_id, substs).unwrap(),
            );
            CValue::Func(func_ref, layout)
        }
        _ => trans_const_place(fx, const_).to_cvalue(fx),
    }
}

fn trans_const_place<'a, 'tcx: 'a>(
    fx: &mut FunctionCx<'a, 'tcx, impl Backend>,
    const_: &'tcx Const<'tcx>,
) -> CPlace<'tcx> {
    let alloc = fx.tcx.const_value_to_allocation(const_);
    //println!("const value: {:?} allocation: {:?}", value, alloc);
    let alloc_id = fx.tcx.alloc_map.lock().allocate(alloc);
    fx.constants.todo.insert(TodoItem::Alloc(alloc_id));
    let data_id = data_id_for_alloc_id(fx.module, alloc_id);
    cplace_for_dataid(fx, const_.ty, data_id)
}

fn data_id_for_alloc_id<B: Backend>(module: &mut Module<B>, alloc_id: AllocId) -> DataId {
    module
        .declare_data(&alloc_id.0.to_string(), Linkage::Local, false)
        .unwrap()
}

fn data_id_for_static<'a, 'tcx: 'a, B: Backend>(tcx: TyCtxt<'a, 'tcx, 'tcx>, module: &mut Module<B>, def_id: DefId) -> DataId {
    let symbol_name = tcx.symbol_name(Instance::mono(tcx, def_id)).as_str();
    let is_mutable = if let ::rustc::hir::Mutability::MutMutable = tcx.is_static(def_id).unwrap() {
        true
    } else {
        !tcx.type_of(def_id).is_freeze(tcx, ParamEnv::reveal_all(), DUMMY_SP)
    };
    module
        .declare_data(&*symbol_name, Linkage::Export, is_mutable)
        .unwrap()
}

fn cplace_for_dataid<'a, 'tcx: 'a>(
    fx: &mut FunctionCx<'a, 'tcx, impl Backend>,
    ty: Ty<'tcx>,
    data_id: DataId,
) -> CPlace<'tcx> {
    let local_data_id = fx.module.declare_data_in_func(data_id, &mut fx.bcx.func);
    let global_ptr = fx.bcx.ins().global_value(types::I64, local_data_id);
    let layout = fx.layout_of(fx.monomorphize(&ty));
    CPlace::Addr(global_ptr, layout)
}

fn define_all_allocs<'a, 'tcx: 'a, B: Backend + 'a>(
    tcx: TyCtxt<'a, 'tcx, 'tcx>,
    module: &mut Module<B>,
    cx: &mut ConstantCx,
) {
    let memory = Memory::<CompileTimeEvaluator>::new(tcx.at(DUMMY_SP), ());

    while let Some(todo_item) = pop_set(&mut cx.todo) {
        let (data_id, alloc) = match todo_item {
            TodoItem::Alloc(alloc_id) => {
                //println!("alloc_id {}", alloc_id);
                let data_id = data_id_for_alloc_id(module, alloc_id);
                let alloc = memory.get(alloc_id).unwrap();
                (data_id, alloc)
            }
            TodoItem::Static(def_id) => {
                //println!("static {:?}", def_id);
                let instance = ty::Instance::mono(tcx, def_id);
                let cid = GlobalId {
                    instance,
                    promoted: None,
                };
                let const_ = tcx.const_eval(ParamEnv::reveal_all().and(cid)).unwrap();

                let alloc = match const_.val {
                    ConstValue::ByRef(alloc, n) if n.bytes() == 0 => alloc,
                    _ => bug!("static const eval returned {:#?}", const_),
                };

                let data_id = data_id_for_static(tcx, module, def_id);
                (data_id, alloc)
            }
        };

        //("data_id {}", data_id);
        if cx.done.contains(&data_id) {
            continue;
        }

        let mut data_ctx = DataContext::new();

        data_ctx.define(
            alloc.bytes.to_vec().into_boxed_slice(),
            match alloc.runtime_mutability {
                AstMutability::Mutable => Writability::Writable,
                AstMutability::Immutable => Writability::Readonly,
            },
        );

        for &(offset, reloc) in alloc.relocations.iter() {
            let data_id = match tcx.alloc_map.lock().get(reloc).unwrap() {
                AllocType::Memory(_) => {
                    cx.todo.insert(TodoItem::Alloc(reloc));
                    data_id_for_alloc_id(module, reloc)
                }
                AllocType::Function(_) => unimplemented!("function static reference"),
                AllocType::Static(def_id) => {
                    cx.todo.insert(TodoItem::Static(def_id));
                    data_id_for_static(tcx, module, def_id)
                }
            };

            let reloc_offset = {
                let endianness = memory.endianness();
                let offset = offset.bytes() as usize;
                let ptr_size = tcx.data_layout.pointer_size;
                let bytes = &alloc.bytes[offset..offset + ptr_size.bytes() as usize];
                read_target_uint(endianness, bytes).unwrap()
            };

            let global_value = module.declare_data_in_data(data_id, &mut data_ctx);
            data_ctx.write_data_addr(reloc_offset as u32, global_value, 0);
        }

        module.define_data(data_id, &data_ctx).unwrap();
        cx.done.insert(data_id);
    }

    assert!(cx.todo.is_empty(), "{:?}", cx.todo);
}

fn pop_set<T: Copy + Eq + ::std::hash::Hash>(set: &mut HashSet<T>) -> Option<T> {
    if let Some(elem) = set.iter().next().map(|elem| *elem) {
        set.remove(&elem);
        Some(elem)
    } else {
        None
    }
}