//! A frontend for building Cranelift IR from other languages.
use crate::ssa::{Block, SSABuilder, SideEffects};
use crate::variable::Variable;
use cranelift_codegen::cursor::{Cursor, FuncCursor};
use cranelift_codegen::entity::{EntitySet, SecondaryMap};
use cranelift_codegen::ir;
use cranelift_codegen::ir::function::DisplayFunction;
use cranelift_codegen::ir::{
    types, AbiParam, DataFlowGraph, Ebb, ExtFuncData, ExternalName, FuncRef, Function, GlobalValue,
    GlobalValueData, Heap, HeapData, Inst, InstBuilder, InstBuilderBase, InstructionData,
    JumpTable, JumpTableData, LibCall, MemFlags, SigRef, Signature, StackSlot, StackSlotData, Type,
    Value, ValueLabel, ValueLabelAssignments, ValueLabelStart,
};
use cranelift_codegen::isa::{TargetFrontendConfig, TargetIsa};
use cranelift_codegen::packed_option::PackedOption;
use std::vec::Vec;

/// Structure used for translating a series of functions into Cranelift IR.
///
/// In order to reduce memory reallocations when compiling multiple functions,
/// `FunctionBuilderContext` holds various data structures which are cleared between
/// functions, rather than dropped, preserving the underlying allocations.
pub struct FunctionBuilderContext {
    ssa: SSABuilder,
    ebbs: SecondaryMap<Ebb, EbbData>,
    types: SecondaryMap<Variable, Type>,
}

/// Temporary object used to build a single Cranelift IR `Function`.
pub struct FunctionBuilder<'a> {
    /// The function currently being built.
    /// This field is public so the function can be re-borrowed.
    pub func: &'a mut Function,

    /// Source location to assign to all new instructions.
    srcloc: ir::SourceLoc,

    func_ctx: &'a mut FunctionBuilderContext,
    position: Position,
}

#[derive(Clone, Default)]
struct EbbData {
    /// An Ebb is "pristine" iff no instructions have been added since the last
    /// call to `switch_to_block()`.
    pristine: bool,

    /// An Ebb is "filled" iff a terminator instruction has been inserted since
    /// the last call to `switch_to_block()`.
    ///
    /// A filled block cannot be pristine.
    filled: bool,

    /// Count of parameters not supplied implicitly by the SSABuilder.
    user_param_count: usize,
}

#[derive(Default)]
struct Position {
    ebb: PackedOption<Ebb>,
    basic_block: PackedOption<Block>,
}

impl Position {
    fn at(ebb: Ebb, basic_block: Block) -> Self {
        Self {
            ebb: PackedOption::from(ebb),
            basic_block: PackedOption::from(basic_block),
        }
    }

    fn is_default(&self) -> bool {
        self.ebb.is_none() && self.basic_block.is_none()
    }
}

impl FunctionBuilderContext {
    /// Creates a FunctionBuilderContext structure. The structure is automatically cleared after
    /// each [`FunctionBuilder`](struct.FunctionBuilder.html) completes translating a function.
    pub fn new() -> Self {
        Self {
            ssa: SSABuilder::new(),
            ebbs: SecondaryMap::new(),
            types: SecondaryMap::new(),
        }
    }

    fn clear(&mut self) {
        self.ssa.clear();
        self.ebbs.clear();
        self.types.clear();
    }

    fn is_empty(&self) -> bool {
        self.ssa.is_empty() && self.ebbs.is_empty() && self.types.is_empty()
    }
}

/// Implementation of the [`InstBuilder`](cranelift_codegen::ir::InstBuilder) that has
/// one convenience method per Cranelift IR instruction.
pub struct FuncInstBuilder<'short, 'long: 'short> {
    builder: &'short mut FunctionBuilder<'long>,
    ebb: Ebb,
}

impl<'short, 'long> FuncInstBuilder<'short, 'long> {
    fn new(builder: &'short mut FunctionBuilder<'long>, ebb: Ebb) -> Self {
        Self { builder, ebb }
    }
}

impl<'short, 'long> InstBuilderBase<'short> for FuncInstBuilder<'short, 'long> {
    fn data_flow_graph(&self) -> &DataFlowGraph {
        &self.builder.func.dfg
    }

    fn data_flow_graph_mut(&mut self) -> &mut DataFlowGraph {
        &mut self.builder.func.dfg
    }

    // This implementation is richer than `InsertBuilder` because we use the data of the
    // instruction being inserted to add related info to the DFG and the SSA building system,
    // and perform debug sanity checks.
    fn build(self, data: InstructionData, ctrl_typevar: Type) -> (Inst, &'short mut DataFlowGraph) {
        // We only insert the Ebb in the layout when an instruction is added to it
        self.builder.ensure_inserted_ebb();

        let inst = self.builder.func.dfg.make_inst(data.clone());
        self.builder.func.dfg.make_inst_results(inst, ctrl_typevar);
        self.builder.func.layout.append_inst(inst, self.ebb);
        if !self.builder.srcloc.is_default() {
            self.builder.func.srclocs[inst] = self.builder.srcloc;
        }

        if data.opcode().is_branch() {
            match data.branch_destination() {
                Some(dest_ebb) => {
                    // If the user has supplied jump arguments we must adapt the arguments of
                    // the destination ebb
                    self.builder.declare_successor(dest_ebb, inst);
                }
                None => {
                    // branch_destination() doesn't detect jump_tables
                    // If jump table we declare all entries successor
                    if let InstructionData::BranchTable {
                        table, destination, ..
                    } = data
                    {
                        // Unlike all other jumps/branches, jump tables are
                        // capable of having the same successor appear
                        // multiple times, so we must deduplicate.
                        let mut unique = EntitySet::<Ebb>::new();
                        for dest_ebb in self
                            .builder
                            .func
                            .jump_tables
                            .get(table)
                            .expect("you are referencing an undeclared jump table")
                            .iter()
                            .filter(|&dest_ebb| unique.insert(*dest_ebb))
                        {
                            self.builder.func_ctx.ssa.declare_ebb_predecessor(
                                *dest_ebb,
                                self.builder.position.basic_block.unwrap(),
                                inst,
                            );
                        }
                        self.builder.func_ctx.ssa.declare_ebb_predecessor(
                            destination,
                            self.builder.position.basic_block.unwrap(),
                            inst,
                        );
                    }
                }
            }
        }
        if data.opcode().is_terminator() {
            self.builder.fill_current_block()
        } else if data.opcode().is_branch() {
            self.builder.move_to_next_basic_block()
        }
        (inst, &mut self.builder.func.dfg)
    }
}

/// This module allows you to create a function in Cranelift IR in a straightforward way, hiding
/// all the complexity of its internal representation.
///
/// The module is parametrized by one type which is the representation of variables in your
/// origin language. It offers a way to conveniently append instruction to your program flow.
/// You are responsible to split your instruction flow into extended blocks (declared with
/// `create_ebb`) whose properties are:
///
/// - branch and jump instructions can only point at the top of extended blocks;
/// - the last instruction of each block is a terminator instruction which has no natural successor,
///   and those instructions can only appear at the end of extended blocks.
///
/// The parameters of Cranelift IR instructions are Cranelift IR values, which can only be created
/// as results of other Cranelift IR instructions. To be able to create variables redefined multiple
/// times in your program, use the `def_var` and `use_var` command, that will maintain the
/// correspondence between your variables and Cranelift IR SSA values.
///
/// The first block for which you call `switch_to_block` will be assumed to be the beginning of
/// the function.
///
/// At creation, a `FunctionBuilder` instance borrows an already allocated `Function` which it
/// modifies with the information stored in the mutable borrowed
/// [`FunctionBuilderContext`](struct.FunctionBuilderContext.html). The function passed in
/// argument should be newly created with
/// [`Function::with_name_signature()`](Function::with_name_signature), whereas the
/// `FunctionBuilderContext` can be kept as is between two function translations.
///
/// # Errors
///
/// The functions below will panic in debug mode whenever you try to modify the Cranelift IR
/// function in a way that violate the coherence of the code. For instance: switching to a new
/// `Ebb` when you haven't filled the current one with a terminator instruction, inserting a
/// return instruction with arguments that don't match the function's signature.
impl<'a> FunctionBuilder<'a> {
    /// Creates a new FunctionBuilder structure that will operate on a `Function` using a
    /// `FunctionBuilderContext`.
    pub fn new(func: &'a mut Function, func_ctx: &'a mut FunctionBuilderContext) -> Self {
        debug_assert!(func_ctx.is_empty());
        Self {
            func,
            srcloc: Default::default(),
            func_ctx,
            position: Position::default(),
        }
    }

    /// Set the source location that should be assigned to all new instructions.
    pub fn set_srcloc(&mut self, srcloc: ir::SourceLoc) {
        self.srcloc = srcloc;
    }

    /// Creates a new `Ebb` and returns its reference.
    pub fn create_ebb(&mut self) -> Ebb {
        let ebb = self.func.dfg.make_ebb();
        self.func_ctx.ssa.declare_ebb_header_block(ebb);
        self.func_ctx.ebbs[ebb] = EbbData {
            filled: false,
            pristine: true,
            user_param_count: 0,
        };
        ebb
    }

    /// After the call to this function, new instructions will be inserted into the designated
    /// block, in the order they are declared. You must declare the types of the Ebb arguments
    /// you will use here.
    ///
    /// When inserting the terminator instruction (which doesn't have a fallthrough to its immediate
    /// successor), the block will be declared filled and it will not be possible to append
    /// instructions to it.
    pub fn switch_to_block(&mut self, ebb: Ebb) {
        // First we check that the previous block has been filled.
        debug_assert!(
            self.position.is_default()
                || self.is_unreachable()
                || self.is_pristine()
                || self.is_filled(),
            "you have to fill your block before switching"
        );
        // We cannot switch to a filled block
        debug_assert!(
            !self.func_ctx.ebbs[ebb].filled,
            "you cannot switch to a block which is already filled"
        );

        let basic_block = self.func_ctx.ssa.header_block(ebb);
        // Then we change the cursor position.
        self.position = Position::at(ebb, basic_block);
    }

    /// Declares that all the predecessors of this block are known.
    ///
    /// Function to call with `ebb` as soon as the last branch instruction to `ebb` has been
    /// created. Forgetting to call this method on every block will cause inconsistencies in the
    /// produced functions.
    pub fn seal_block(&mut self, ebb: Ebb) {
        let side_effects = self.func_ctx.ssa.seal_ebb_header_block(ebb, self.func);
        self.handle_ssa_side_effects(side_effects);
    }

    /// Effectively calls seal_block on all blocks in the function.
    ///
    /// It's more efficient to seal `Ebb`s as soon as possible, during
    /// translation, but for frontends where this is impractical to do, this
    /// function can be used at the end of translating all blocks to ensure
    /// that everything is sealed.
    pub fn seal_all_blocks(&mut self) {
        let side_effects = self.func_ctx.ssa.seal_all_ebb_header_blocks(self.func);
        self.handle_ssa_side_effects(side_effects);
    }

    /// In order to use a variable in a `use_var`, you need to declare its type with this method.
    pub fn declare_var(&mut self, var: Variable, ty: Type) {
        self.func_ctx.types[var] = ty;
    }

    /// Returns the Cranelift IR value corresponding to the utilization at the current program
    /// position of a previously defined user variable.
    pub fn use_var(&mut self, var: Variable) -> Value {
        let (val, side_effects) = {
            let ty = *self.func_ctx.types.get(var).unwrap_or_else(|| {
                panic!(
                    "variable {:?} is used but its type has not been declared",
                    var
                )
            });
            self.func_ctx
                .ssa
                .use_var(self.func, var, ty, self.position.basic_block.unwrap())
        };
        self.handle_ssa_side_effects(side_effects);
        val
    }

    /// Register a new definition of a user variable. The type of the value must be
    /// the same as the type registered for the variable.
    pub fn def_var(&mut self, var: Variable, val: Value) {
        debug_assert_eq!(
            *self.func_ctx.types.get(var).unwrap_or_else(|| panic!(
                "variable {:?} is used but its type has not been declared",
                var
            )),
            self.func.dfg.value_type(val),
            "declared type of variable {:?} doesn't match type of value {}",
            var,
            val
        );

        self.func_ctx
            .ssa
            .def_var(var, val, self.position.basic_block.unwrap());
    }

    /// Set label for Value
    ///
    /// This will not do anything unless `func.dfg.collect_debug_info` is called first.
    pub fn set_val_label(&mut self, val: Value, label: ValueLabel) {
        if let Some(values_labels) = self.func.dfg.values_labels.as_mut() {
            use std::collections::hash_map::Entry;

            let start = ValueLabelStart {
                from: self.srcloc,
                label,
            };

            match values_labels.entry(val) {
                Entry::Occupied(mut e) => match e.get_mut() {
                    ValueLabelAssignments::Starts(starts) => starts.push(start),
                    _ => panic!("Unexpected ValueLabelAssignments at this stage"),
                },
                Entry::Vacant(e) => {
                    e.insert(ValueLabelAssignments::Starts(vec![start]));
                }
            }
        }
    }

    /// Creates a jump table in the function, to be used by `br_table` instructions.
    pub fn create_jump_table(&mut self, data: JumpTableData) -> JumpTable {
        self.func.create_jump_table(data)
    }

    /// Creates a stack slot in the function, to be used by `stack_load`, `stack_store` and
    /// `stack_addr` instructions.
    pub fn create_stack_slot(&mut self, data: StackSlotData) -> StackSlot {
        self.func.create_stack_slot(data)
    }

    /// Adds a signature which can later be used to declare an external function import.
    pub fn import_signature(&mut self, signature: Signature) -> SigRef {
        self.func.import_signature(signature)
    }

    /// Declare an external function import.
    pub fn import_function(&mut self, data: ExtFuncData) -> FuncRef {
        self.func.import_function(data)
    }

    /// Declares a global value accessible to the function.
    pub fn create_global_value(&mut self, data: GlobalValueData) -> GlobalValue {
        self.func.create_global_value(data)
    }

    /// Declares a heap accessible to the function.
    pub fn create_heap(&mut self, data: HeapData) -> Heap {
        self.func.create_heap(data)
    }

    /// Returns an object with the [`InstBuilder`](cranelift_codegen::ir::InstBuilder)
    /// trait that allows to conveniently append an instruction to the current `Ebb` being built.
    pub fn ins<'short>(&'short mut self) -> FuncInstBuilder<'short, 'a> {
        let ebb = self
            .position
            .ebb
            .expect("Please call switch_to_block before inserting instructions");
        FuncInstBuilder::new(self, ebb)
    }

    /// Make sure that the current EBB is inserted in the layout.
    pub fn ensure_inserted_ebb(&mut self) {
        let ebb = self.position.ebb.unwrap();
        if self.func_ctx.ebbs[ebb].pristine {
            if !self.func.layout.is_ebb_inserted(ebb) {
                self.func.layout.append_ebb(ebb);
            }
            self.func_ctx.ebbs[ebb].pristine = false;
        } else {
            debug_assert!(
                !self.func_ctx.ebbs[ebb].filled,
                "you cannot add an instruction to a block already filled"
            );
        }
    }

    /// Returns a `FuncCursor` pointed at the current position ready for inserting instructions.
    ///
    /// This can be used to insert SSA code that doesn't need to access locals and that doesn't
    /// need to know about `FunctionBuilder` at all.
    pub fn cursor(&mut self) -> FuncCursor {
        self.ensure_inserted_ebb();
        FuncCursor::new(self.func)
            .with_srcloc(self.srcloc)
            .at_bottom(self.position.ebb.unwrap())
    }

    /// Append parameters to the given `Ebb` corresponding to the function
    /// parameters. This can be used to set up the ebb parameters for the
    /// entry block.
    pub fn append_ebb_params_for_function_params(&mut self, ebb: Ebb) {
        debug_assert!(
            !self.func_ctx.ssa.has_any_predecessors(ebb),
            "ebb parameters for function parameters should only be added to the entry block"
        );

        // These parameters count as "user" parameters here because they aren't
        // inserted by the SSABuilder.
        let user_param_count = &mut self.func_ctx.ebbs[ebb].user_param_count;
        for argtyp in &self.func.signature.params {
            *user_param_count += 1;
            self.func.dfg.append_ebb_param(ebb, argtyp.value_type);
        }
    }

    /// Append parameters to the given `Ebb` corresponding to the function
    /// return values. This can be used to set up the ebb parameters for a
    /// function exit block.
    pub fn append_ebb_params_for_function_returns(&mut self, ebb: Ebb) {
        // These parameters count as "user" parameters here because they aren't
        // inserted by the SSABuilder.
        let user_param_count = &mut self.func_ctx.ebbs[ebb].user_param_count;
        for argtyp in &self.func.signature.returns {
            *user_param_count += 1;
            self.func.dfg.append_ebb_param(ebb, argtyp.value_type);
        }
    }

    /// Declare that translation of the current function is complete. This
    /// resets the state of the `FunctionBuilder` in preparation to be used
    /// for another function.
    pub fn finalize(&mut self) {
        // Check that all the `Ebb`s are filled and sealed.
        debug_assert!(
            self.func_ctx
                .ebbs
                .iter()
                .all(|(ebb, ebb_data)| ebb_data.pristine || self.func_ctx.ssa.is_sealed(ebb)),
            "all blocks should be sealed before dropping a FunctionBuilder"
        );
        debug_assert!(
            self.func_ctx
                .ebbs
                .values()
                .all(|ebb_data| ebb_data.pristine || ebb_data.filled),
            "all blocks should be filled before dropping a FunctionBuilder"
        );

        // In debug mode, check that all blocks are valid basic blocks.
        #[cfg(feature = "basic-blocks")]
        #[cfg(debug_assertions)]
        {
            // Iterate manually to provide more helpful error messages.
            for ebb in self.func_ctx.ebbs.keys() {
                if let Err((inst, _msg)) = self.func.is_ebb_basic(ebb) {
                    let inst_str = self.func.dfg.display_inst(inst, None);
                    panic!("{} failed basic block invariants on {}", ebb, inst_str);
                }
            }
        }

        // Clear the state (but preserve the allocated buffers) in preparation
        // for translation another function.
        self.func_ctx.clear();

        // Reset srcloc and position to initial states.
        self.srcloc = Default::default();
        self.position = Position::default();
    }
}

/// All the functions documented in the previous block are write-only and help you build a valid
/// Cranelift IR functions via multiple debug asserts. However, you might need to improve the
/// performance of your translation perform more complex transformations to your Cranelift IR
/// function. The functions below help you inspect the function you're creating and modify it
/// in ways that can be unsafe if used incorrectly.
impl<'a> FunctionBuilder<'a> {
    /// Retrieves all the parameters for an `Ebb` currently inferred from the jump instructions
    /// inserted that target it and the SSA construction.
    pub fn ebb_params(&self, ebb: Ebb) -> &[Value] {
        self.func.dfg.ebb_params(ebb)
    }

    /// Retrieves the signature with reference `sigref` previously added with `import_signature`.
    pub fn signature(&self, sigref: SigRef) -> Option<&Signature> {
        self.func.dfg.signatures.get(sigref)
    }

    /// Creates a parameter for a specific `Ebb` by appending it to the list of already existing
    /// parameters.
    ///
    /// **Note:** this function has to be called at the creation of the `Ebb` before adding
    /// instructions to it, otherwise this could interfere with SSA construction.
    pub fn append_ebb_param(&mut self, ebb: Ebb, ty: Type) -> Value {
        debug_assert!(
            self.func_ctx.ebbs[ebb].pristine,
            "You can't add EBB parameters after adding any instruction"
        );
        debug_assert_eq!(
            self.func_ctx.ebbs[ebb].user_param_count,
            self.func.dfg.num_ebb_params(ebb)
        );
        self.func_ctx.ebbs[ebb].user_param_count += 1;
        self.func.dfg.append_ebb_param(ebb, ty)
    }

    /// Returns the result values of an instruction.
    pub fn inst_results(&self, inst: Inst) -> &[Value] {
        self.func.dfg.inst_results(inst)
    }

    /// Changes the destination of a jump instruction after creation.
    ///
    /// **Note:** You are responsible for maintaining the coherence with the arguments of
    /// other jump instructions.
    pub fn change_jump_destination(&mut self, inst: Inst, new_dest: Ebb) {
        let old_dest = self.func.dfg[inst]
            .branch_destination_mut()
            .expect("you want to change the jump destination of a non-jump instruction");
        let pred = self.func_ctx.ssa.remove_ebb_predecessor(*old_dest, inst);
        *old_dest = new_dest;
        self.func_ctx
            .ssa
            .declare_ebb_predecessor(new_dest, pred, inst);
    }

    /// Returns `true` if and only if the current `Ebb` is sealed and has no predecessors declared.
    ///
    /// The entry block of a function is never unreachable.
    pub fn is_unreachable(&self) -> bool {
        let is_entry = match self.func.layout.entry_block() {
            None => false,
            Some(entry) => self.position.ebb.unwrap() == entry,
        };
        !is_entry
            && self.func_ctx.ssa.is_sealed(self.position.ebb.unwrap())
            && !self
                .func_ctx
                .ssa
                .has_any_predecessors(self.position.ebb.unwrap())
    }

    /// Returns `true` if and only if no instructions have been added since the last call to
    /// `switch_to_block`.
    pub fn is_pristine(&self) -> bool {
        self.func_ctx.ebbs[self.position.ebb.unwrap()].pristine
    }

    /// Returns `true` if and only if a terminator instruction has been inserted since the
    /// last call to `switch_to_block`.
    pub fn is_filled(&self) -> bool {
        self.func_ctx.ebbs[self.position.ebb.unwrap()].filled
    }

    /// Returns a displayable object for the function as it is.
    ///
    /// Useful for debug purposes. Use it with `None` for standard printing.
    // Clippy thinks the lifetime that follows is needless, but rustc needs it
    #[cfg_attr(feature = "cargo-clippy", allow(clippy::needless_lifetimes))]
    pub fn display<'b, I: Into<Option<&'b dyn TargetIsa>>>(&'b self, isa: I) -> DisplayFunction {
        self.func.display(isa)
    }
}

/// Helper functions
impl<'a> FunctionBuilder<'a> {
    /// Calls libc.memcpy
    ///
    /// Copies the `size` bytes from `src` to `dest`, assumes that `src + size`
    /// won't overlap onto `dest`. If `dest` and `src` overlap, the behavior is
    /// undefined. Applications in which `dest` and `src` might overlap should
    /// use `call_memmove` instead.
    pub fn call_memcpy(
        &mut self,
        config: TargetFrontendConfig,
        dest: Value,
        src: Value,
        size: Value,
    ) {
        let pointer_type = config.pointer_type();
        let signature = {
            let mut s = Signature::new(config.default_call_conv);
            s.params.push(AbiParam::new(pointer_type));
            s.params.push(AbiParam::new(pointer_type));
            s.params.push(AbiParam::new(pointer_type));
            self.import_signature(s)
        };

        let libc_memcpy = self.import_function(ExtFuncData {
            name: ExternalName::LibCall(LibCall::Memcpy),
            signature,
            colocated: false,
        });

        self.ins().call(libc_memcpy, &[dest, src, size]);
    }

    /// Optimised memcpy for small copies.
    pub fn emit_small_memcpy(
        &mut self,
        config: TargetFrontendConfig,
        dest: Value,
        src: Value,
        size: u64,
        dest_align: u8,
        src_align: u8,
    ) {
        // Currently the result of guess work, not actual profiling.
        const THRESHOLD: u64 = 4;

        if size == 0 {
            return;
        }

        let access_size = greatest_divisible_power_of_two(size);
        assert!(
            access_size.is_power_of_two(),
            "`size` is not a power of two"
        );
        assert!(
            access_size >= u64::from(::core::cmp::min(src_align, dest_align)),
            "`size` is smaller than `dest` and `src`'s alignment value."
        );

        let (access_size, int_type) = if access_size <= 8 {
            (access_size, Type::int((access_size * 8) as u16).unwrap())
        } else {
            (8, types::I64)
        };

        let load_and_store_amount = size / access_size;

        if load_and_store_amount > THRESHOLD {
            let size_value = self.ins().iconst(config.pointer_type(), size as i64);
            self.call_memcpy(config, dest, src, size_value);
            return;
        }

        let mut flags = MemFlags::new();
        flags.set_aligned();

        for i in 0..load_and_store_amount {
            let offset = (access_size * i) as i32;
            let value = self.ins().load(int_type, flags, src, offset);
            self.ins().store(flags, value, dest, offset);
        }
    }

    /// Calls libc.memset
    ///
    /// Writes `size` bytes of i8 value `ch` to memory starting at `buffer`.
    pub fn call_memset(
        &mut self,
        config: TargetFrontendConfig,
        buffer: Value,
        ch: Value,
        size: Value,
    ) {
        let pointer_type = config.pointer_type();
        let signature = {
            let mut s = Signature::new(config.default_call_conv);
            s.params.push(AbiParam::new(pointer_type));
            s.params.push(AbiParam::new(types::I32));
            s.params.push(AbiParam::new(pointer_type));
            self.import_signature(s)
        };

        let libc_memset = self.import_function(ExtFuncData {
            name: ExternalName::LibCall(LibCall::Memset),
            signature,
            colocated: false,
        });

        let ch = self.ins().uextend(types::I32, ch);
        self.ins().call(libc_memset, &[buffer, ch, size]);
    }

    /// Calls libc.memset
    ///
    /// Writes `size` bytes of value `ch` to memory starting at `buffer`.
    pub fn emit_small_memset(
        &mut self,
        config: TargetFrontendConfig,
        buffer: Value,
        ch: u8,
        size: u64,
        buffer_align: u8,
    ) {
        // Currently the result of guess work, not actual profiling.
        const THRESHOLD: u64 = 4;

        if size == 0 {
            return;
        }

        let access_size = greatest_divisible_power_of_two(size);
        assert!(
            access_size.is_power_of_two(),
            "`size` is not a power of two"
        );
        assert!(
            access_size >= u64::from(buffer_align),
            "`size` is smaller than `dest` and `src`'s alignment value."
        );

        let (access_size, int_type) = if access_size <= 8 {
            (access_size, Type::int((access_size * 8) as u16).unwrap())
        } else {
            (8, types::I64)
        };

        let load_and_store_amount = size / access_size;

        if load_and_store_amount > THRESHOLD {
            let ch = self.ins().iconst(types::I8, i64::from(ch));
            let size = self.ins().iconst(config.pointer_type(), size as i64);
            self.call_memset(config, buffer, ch, size);
        } else {
            let mut flags = MemFlags::new();
            flags.set_aligned();

            let ch = u64::from(ch);
            let raw_value = if int_type == types::I64 {
                (ch << 32) | (ch << 16) | (ch << 8) | ch
            } else if int_type == types::I32 {
                (ch << 16) | (ch << 8) | ch
            } else if int_type == types::I16 {
                (ch << 8) | ch
            } else {
                assert_eq!(int_type, types::I8);
                ch
            };

            let value = self.ins().iconst(int_type, raw_value as i64);
            for i in 0..load_and_store_amount {
                let offset = (access_size * i) as i32;
                self.ins().store(flags, value, buffer, offset);
            }
        }
    }

    /// Calls libc.memmove
    ///
    /// Copies `size` bytes from memory starting at `source` to memory starting
    /// at `dest`. `source` is always read before writing to `dest`.
    pub fn call_memmove(
        &mut self,
        config: TargetFrontendConfig,
        dest: Value,
        source: Value,
        size: Value,
    ) {
        let pointer_type = config.pointer_type();
        let signature = {
            let mut s = Signature::new(config.default_call_conv);
            s.params.push(AbiParam::new(pointer_type));
            s.params.push(AbiParam::new(pointer_type));
            s.params.push(AbiParam::new(pointer_type));
            self.import_signature(s)
        };

        let libc_memmove = self.import_function(ExtFuncData {
            name: ExternalName::LibCall(LibCall::Memmove),
            signature,
            colocated: false,
        });

        self.ins().call(libc_memmove, &[dest, source, size]);
    }

    /// Optimised memmove for small moves.
    pub fn emit_small_memmove(
        &mut self,
        config: TargetFrontendConfig,
        dest: Value,
        src: Value,
        size: u64,
        dest_align: u8,
        src_align: u8,
    ) {
        // Currently the result of guess work, not actual profiling.
        const THRESHOLD: u64 = 4;

        let access_size = greatest_divisible_power_of_two(size);
        assert!(
            access_size.is_power_of_two(),
            "`size` is not a power of two"
        );
        assert!(
            access_size >= u64::from(::core::cmp::min(src_align, dest_align)),
            "`size` is smaller than `dest` and `src`'s alignment value."
        );
        let load_and_store_amount = size / access_size;

        if load_and_store_amount > THRESHOLD {
            let size_value = self.ins().iconst(config.pointer_type(), size as i64);
            self.call_memmove(config, dest, src, size_value);
            return;
        }

        let mut flags = MemFlags::new();
        flags.set_aligned();

        // Load all of the memory first in case `dest` overlaps.
        let registers: Vec<_> = (0..load_and_store_amount)
            .map(|i| {
                let offset = (access_size * i) as i32;
                (
                    self.ins().load(config.pointer_type(), flags, src, offset),
                    offset,
                )
            })
            .collect();

        for (value, offset) in registers {
            self.ins().store(flags, value, dest, offset);
        }
    }
}

fn greatest_divisible_power_of_two(size: u64) -> u64 {
    (size as i64 & -(size as i64)) as u64
}

// Helper functions
impl<'a> FunctionBuilder<'a> {
    fn move_to_next_basic_block(&mut self) {
        self.position.basic_block = PackedOption::from(
            self.func_ctx
                .ssa
                .declare_ebb_body_block(self.position.basic_block.unwrap()),
        );
    }

    /// An Ebb is 'filled' when a terminator instruction is present.
    fn fill_current_block(&mut self) {
        self.func_ctx.ebbs[self.position.ebb.unwrap()].filled = true;
    }

    fn declare_successor(&mut self, dest_ebb: Ebb, jump_inst: Inst) {
        self.func_ctx.ssa.declare_ebb_predecessor(
            dest_ebb,
            self.position.basic_block.unwrap(),
            jump_inst,
        );
    }

    fn handle_ssa_side_effects(&mut self, side_effects: SideEffects) {
        for split_ebb in side_effects.split_ebbs_created {
            self.func_ctx.ebbs[split_ebb].filled = true
        }
        for modified_ebb in side_effects.instructions_added_to_ebbs {
            self.func_ctx.ebbs[modified_ebb].pristine = false
        }
    }
}

#[cfg(test)]
mod tests {
    use super::greatest_divisible_power_of_two;
    use crate::frontend::{FunctionBuilder, FunctionBuilderContext};
    use crate::Variable;
    use cranelift_codegen::entity::EntityRef;
    use cranelift_codegen::ir::types::*;
    use cranelift_codegen::ir::{AbiParam, ExternalName, Function, InstBuilder, Signature};
    use cranelift_codegen::isa::CallConv;
    use cranelift_codegen::settings;
    use cranelift_codegen::verifier::verify_function;
    use std::string::ToString;

    fn sample_function(lazy_seal: bool) {
        let mut sig = Signature::new(CallConv::SystemV);
        sig.returns.push(AbiParam::new(I32));
        sig.params.push(AbiParam::new(I32));

        let mut fn_ctx = FunctionBuilderContext::new();
        let mut func = Function::with_name_signature(ExternalName::testcase("sample"), sig);
        {
            let mut builder = FunctionBuilder::new(&mut func, &mut fn_ctx);

            let block0 = builder.create_ebb();
            let block1 = builder.create_ebb();
            let block2 = builder.create_ebb();
            let block3 = builder.create_ebb();
            let x = Variable::new(0);
            let y = Variable::new(1);
            let z = Variable::new(2);
            builder.declare_var(x, I32);
            builder.declare_var(y, I32);
            builder.declare_var(z, I32);
            builder.append_ebb_params_for_function_params(block0);

            builder.switch_to_block(block0);
            if !lazy_seal {
                builder.seal_block(block0);
            }
            {
                let tmp = builder.ebb_params(block0)[0]; // the first function parameter
                builder.def_var(x, tmp);
            }
            {
                let tmp = builder.ins().iconst(I32, 2);
                builder.def_var(y, tmp);
            }
            {
                let arg1 = builder.use_var(x);
                let arg2 = builder.use_var(y);
                let tmp = builder.ins().iadd(arg1, arg2);
                builder.def_var(z, tmp);
            }
            builder.ins().jump(block1, &[]);

            builder.switch_to_block(block1);
            {
                let arg1 = builder.use_var(y);
                let arg2 = builder.use_var(z);
                let tmp = builder.ins().iadd(arg1, arg2);
                builder.def_var(z, tmp);
            }
            {
                let arg = builder.use_var(y);
                builder.ins().brnz(arg, block3, &[]);
            }
            builder.ins().jump(block2, &[]);

            builder.switch_to_block(block2);
            if !lazy_seal {
                builder.seal_block(block2);
            }
            {
                let arg1 = builder.use_var(z);
                let arg2 = builder.use_var(x);
                let tmp = builder.ins().isub(arg1, arg2);
                builder.def_var(z, tmp);
            }
            {
                let arg = builder.use_var(y);
                builder.ins().return_(&[arg]);
            }

            builder.switch_to_block(block3);
            if !lazy_seal {
                builder.seal_block(block3);
            }

            {
                let arg1 = builder.use_var(y);
                let arg2 = builder.use_var(x);
                let tmp = builder.ins().isub(arg1, arg2);
                builder.def_var(y, tmp);
            }
            builder.ins().jump(block1, &[]);
            if !lazy_seal {
                builder.seal_block(block1);
            }

            if lazy_seal {
                builder.seal_all_blocks();
            }

            builder.finalize();
        }

        let flags = settings::Flags::new(settings::builder());
        // println!("{}", func.display(None));
        if let Err(errors) = verify_function(&func, &flags) {
            panic!("{}\n{}", func.display(None), errors)
        }
    }

    #[test]
    fn sample() {
        sample_function(false)
    }

    #[test]
    fn sample_with_lazy_seal() {
        sample_function(true)
    }

    #[test]
    fn memcpy() {
        use core::str::FromStr;
        use cranelift_codegen::{isa, settings};

        let shared_builder = settings::builder();
        let shared_flags = settings::Flags::new(shared_builder);

        let triple = ::target_lexicon::Triple::from_str("arm").expect("Couldn't create arm triple");

        let target = isa::lookup(triple)
            .ok()
            .map(|b| b.finish(shared_flags))
            .expect("This test requires arm support.");

        let mut sig = Signature::new(target.default_call_conv());
        sig.returns.push(AbiParam::new(I32));

        let mut fn_ctx = FunctionBuilderContext::new();
        let mut func = Function::with_name_signature(ExternalName::testcase("sample"), sig);
        {
            let mut builder = FunctionBuilder::new(&mut func, &mut fn_ctx);

            let block0 = builder.create_ebb();
            let x = Variable::new(0);
            let y = Variable::new(1);
            let z = Variable::new(2);
            builder.declare_var(x, target.pointer_type());
            builder.declare_var(y, target.pointer_type());
            builder.declare_var(z, I32);
            builder.append_ebb_params_for_function_params(block0);
            builder.switch_to_block(block0);

            let src = builder.use_var(x);
            let dest = builder.use_var(y);
            let size = builder.use_var(y);
            builder.call_memcpy(target.frontend_config(), dest, src, size);
            builder.ins().return_(&[size]);

            builder.seal_all_blocks();
            builder.finalize();
        }

        assert_eq!(
            func.display(None).to_string(),
            "function %sample() -> i32 system_v {
    sig0 = (i32, i32, i32) system_v
    fn0 = %Memcpy sig0

ebb0:
    v3 = iconst.i32 0
    v1 -> v3
    v2 = iconst.i32 0
    v0 -> v2
    call fn0(v1, v0, v1)
    return v1
}
"
        );
    }

    #[test]
    fn small_memcpy() {
        use core::str::FromStr;
        use cranelift_codegen::{isa, settings};

        let shared_builder = settings::builder();
        let shared_flags = settings::Flags::new(shared_builder);

        let triple = ::target_lexicon::Triple::from_str("arm").expect("Couldn't create arm triple");

        let target = isa::lookup(triple)
            .ok()
            .map(|b| b.finish(shared_flags))
            .expect("This test requires arm support.");

        let mut sig = Signature::new(target.default_call_conv());
        sig.returns.push(AbiParam::new(I32));

        let mut fn_ctx = FunctionBuilderContext::new();
        let mut func = Function::with_name_signature(ExternalName::testcase("sample"), sig);
        {
            let mut builder = FunctionBuilder::new(&mut func, &mut fn_ctx);

            let block0 = builder.create_ebb();
            let x = Variable::new(0);
            let y = Variable::new(16);
            builder.declare_var(x, target.pointer_type());
            builder.declare_var(y, target.pointer_type());
            builder.append_ebb_params_for_function_params(block0);
            builder.switch_to_block(block0);

            let src = builder.use_var(x);
            let dest = builder.use_var(y);
            let size = 8;
            builder.emit_small_memcpy(target.frontend_config(), dest, src, size, 8, 8);
            builder.ins().return_(&[dest]);

            builder.seal_all_blocks();
            builder.finalize();
        }

        assert_eq!(
            func.display(None).to_string(),
            "function %sample() -> i32 system_v {
ebb0:
    v4 = iconst.i32 0
    v1 -> v4
    v3 = iconst.i32 0
    v0 -> v3
    v2 = load.i64 aligned v0
    store aligned v2, v1
    return v1
}
"
        );
    }

    #[test]
    fn not_so_small_memcpy() {
        use core::str::FromStr;
        use cranelift_codegen::{isa, settings};

        let shared_builder = settings::builder();
        let shared_flags = settings::Flags::new(shared_builder);

        let triple = ::target_lexicon::Triple::from_str("arm").expect("Couldn't create arm triple");

        let target = isa::lookup(triple)
            .ok()
            .map(|b| b.finish(shared_flags))
            .expect("This test requires arm support.");

        let mut sig = Signature::new(target.default_call_conv());
        sig.returns.push(AbiParam::new(I32));

        let mut fn_ctx = FunctionBuilderContext::new();
        let mut func = Function::with_name_signature(ExternalName::testcase("sample"), sig);
        {
            let mut builder = FunctionBuilder::new(&mut func, &mut fn_ctx);

            let block0 = builder.create_ebb();
            let x = Variable::new(0);
            let y = Variable::new(16);
            builder.declare_var(x, target.pointer_type());
            builder.declare_var(y, target.pointer_type());
            builder.append_ebb_params_for_function_params(block0);
            builder.switch_to_block(block0);

            let src = builder.use_var(x);
            let dest = builder.use_var(y);
            let size = 8192;
            builder.emit_small_memcpy(target.frontend_config(), dest, src, size, 8, 8);
            builder.ins().return_(&[dest]);

            builder.seal_all_blocks();
            builder.finalize();
        }

        assert_eq!(
            func.display(None).to_string(),
            "function %sample() -> i32 system_v {
    sig0 = (i32, i32, i32) system_v
    fn0 = %Memcpy sig0

ebb0:
    v4 = iconst.i32 0
    v1 -> v4
    v3 = iconst.i32 0
    v0 -> v3
    v2 = iconst.i32 8192
    call fn0(v1, v0, v2)
    return v1
}
"
        );
    }

    #[test]
    fn small_memset() {
        use core::str::FromStr;
        use cranelift_codegen::{isa, settings};

        let shared_builder = settings::builder();
        let shared_flags = settings::Flags::new(shared_builder);

        let triple = ::target_lexicon::Triple::from_str("arm").expect("Couldn't create arm triple");

        let target = isa::lookup(triple)
            .ok()
            .map(|b| b.finish(shared_flags))
            .expect("This test requires arm support.");

        let mut sig = Signature::new(target.default_call_conv());
        sig.returns.push(AbiParam::new(I32));

        let mut fn_ctx = FunctionBuilderContext::new();
        let mut func = Function::with_name_signature(ExternalName::testcase("sample"), sig);
        {
            let mut builder = FunctionBuilder::new(&mut func, &mut fn_ctx);

            let block0 = builder.create_ebb();
            let y = Variable::new(16);
            builder.declare_var(y, target.pointer_type());
            builder.append_ebb_params_for_function_params(block0);
            builder.switch_to_block(block0);

            let dest = builder.use_var(y);
            let size = 8;
            builder.emit_small_memset(target.frontend_config(), dest, 1, size, 8);
            builder.ins().return_(&[dest]);

            builder.seal_all_blocks();
            builder.finalize();
        }

        assert_eq!(
            func.display(None).to_string(),
            "function %sample() -> i32 system_v {
ebb0:
    v2 = iconst.i32 0
    v0 -> v2
    v1 = iconst.i64 0x0001_0001_0101
    store aligned v1, v0
    return v0
}
"
        );
    }

    #[test]
    fn not_so_small_memset() {
        use core::str::FromStr;
        use cranelift_codegen::{isa, settings};

        let shared_builder = settings::builder();
        let shared_flags = settings::Flags::new(shared_builder);

        let triple = ::target_lexicon::Triple::from_str("arm").expect("Couldn't create arm triple");

        let target = isa::lookup(triple)
            .ok()
            .map(|b| b.finish(shared_flags))
            .expect("This test requires arm support.");

        let mut sig = Signature::new(target.default_call_conv());
        sig.returns.push(AbiParam::new(I32));

        let mut fn_ctx = FunctionBuilderContext::new();
        let mut func = Function::with_name_signature(ExternalName::testcase("sample"), sig);
        {
            let mut builder = FunctionBuilder::new(&mut func, &mut fn_ctx);

            let block0 = builder.create_ebb();
            let y = Variable::new(16);
            builder.declare_var(y, target.pointer_type());
            builder.append_ebb_params_for_function_params(block0);
            builder.switch_to_block(block0);

            let dest = builder.use_var(y);
            let size = 8192;
            builder.emit_small_memset(target.frontend_config(), dest, 1, size, 8);
            builder.ins().return_(&[dest]);

            builder.seal_all_blocks();
            builder.finalize();
        }

        assert_eq!(
            func.display(None).to_string(),
            "function %sample() -> i32 system_v {
    sig0 = (i32, i32, i32) system_v
    fn0 = %Memset sig0

ebb0:
    v4 = iconst.i32 0
    v0 -> v4
    v1 = iconst.i8 1
    v2 = iconst.i32 8192
    v3 = uextend.i32 v1
    call fn0(v0, v3, v2)
    return v0
}
"
        );
    }

    #[test]
    fn test_greatest_divisible_power_of_two() {
        assert_eq!(64, greatest_divisible_power_of_two(64));
        assert_eq!(16, greatest_divisible_power_of_two(48));
        assert_eq!(8, greatest_divisible_power_of_two(24));
        assert_eq!(1, greatest_divisible_power_of_two(25));
    }
}