//! Legalize instructions.
//!
//! A legal instruction is one that can be mapped directly to a machine code instruction for the
//! target ISA. The `legalize_function()` function takes as input any function and transforms it
//! into an equivalent function using only legal instructions.
//!
//! The characteristics of legal instructions depend on the target ISA, so any given instruction
//! can be legal for one ISA and illegal for another.
//!
//! Besides transforming instructions, the legalizer also fills out the `function.encodings` map
//! which provides a legal encoding recipe for every instruction.
//!
//! The legalizer does not deal with register allocation constraints. These constraints are derived
//! from the encoding recipes, and solved later by the register allocator.

use crate::bitset::BitSet;
use crate::cursor::{Cursor, FuncCursor};
use crate::flowgraph::ControlFlowGraph;
use crate::ir::types::I32;
use crate::ir::{self, InstBuilder, MemFlags};
use crate::isa::TargetIsa;
use crate::timing;

mod boundary;
mod call;
mod globalvalue;
mod heap;
mod libcall;
mod split;
mod table;

use self::call::expand_call;
use self::globalvalue::expand_global_value;
use self::heap::expand_heap_addr;
use self::libcall::expand_as_libcall;
use self::table::expand_table_addr;

/// Legalize `inst` for `isa`. Return true if any changes to the code were
/// made; return false if the instruction was successfully encoded as is.
fn legalize_inst(
    inst: ir::Inst,
    pos: &mut FuncCursor,
    cfg: &mut ControlFlowGraph,
    isa: &dyn TargetIsa,
) -> bool {
    let opcode = pos.func.dfg[inst].opcode();

    // Check for ABI boundaries that need to be converted to the legalized signature.
    if opcode.is_call() {
        if boundary::handle_call_abi(inst, pos.func, cfg) {
            return true;
        }
    } else if opcode.is_return() {
        if boundary::handle_return_abi(inst, pos.func, cfg) {
            return true;
        }
    } else if opcode.is_branch() {
        split::simplify_branch_arguments(&mut pos.func.dfg, inst);
    }

    match pos.func.update_encoding(inst, isa) {
        Ok(()) => false,
        Err(action) => {
            // We should transform the instruction into legal equivalents.
            // If the current instruction was replaced, we need to double back and revisit
            // the expanded sequence. This is both to assign encodings and possible to
            // expand further.
            // There's a risk of infinite looping here if the legalization patterns are
            // unsound. Should we attempt to detect that?
            if action(inst, pos.func, cfg, isa) {
                return true;
            }

            // We don't have any pattern expansion for this instruction either.
            // Try converting it to a library call as a last resort.
            expand_as_libcall(inst, pos.func, isa)
        }
    }
}

/// Legalize `func` for `isa`.
///
/// - Transform any instructions that don't have a legal representation in `isa`.
/// - Fill out `func.encodings`.
///
pub fn legalize_function(func: &mut ir::Function, cfg: &mut ControlFlowGraph, isa: &dyn TargetIsa) {
    let _tt = timing::legalize();
    debug_assert!(cfg.is_valid());

    boundary::legalize_signatures(func, isa);

    func.encodings.resize(func.dfg.num_insts());

    let mut pos = FuncCursor::new(func);

    // Process EBBs in layout order. Some legalization actions may split the current EBB or append
    // new ones to the end. We need to make sure we visit those new EBBs too.
    while let Some(_ebb) = pos.next_ebb() {
        // Keep track of the cursor position before the instruction being processed, so we can
        // double back when replacing instructions.
        let mut prev_pos = pos.position();

        while let Some(inst) = pos.next_inst() {
            if legalize_inst(inst, &mut pos, cfg, isa) {
                // Go back and legalize the inserted return value conversion instructions.
                pos.set_position(prev_pos);
            } else {
                // Remember this position in case we need to double back.
                prev_pos = pos.position();
            }
        }
    }

    // Now that we've lowered all br_tables, we don't need the jump tables anymore.
    if !isa.flags().jump_tables_enabled() {
        pos.func.jump_tables.clear();
    }
}

// Include legalization patterns that were generated by `gen_legalizer.py` from the `XForms` in
// `cranelift-codegen/meta-python/base/legalize.py`.
//
// Concretely, this defines private functions `narrow()`, and `expand()`.
include!(concat!(env!("OUT_DIR"), "/legalizer.rs"));

/// Custom expansion for conditional trap instructions.
/// TODO: Add CFG support to the Python patterns so we won't have to do this.
fn expand_cond_trap(
    inst: ir::Inst,
    func: &mut ir::Function,
    cfg: &mut ControlFlowGraph,
    _isa: &dyn TargetIsa,
) {
    // Parse the instruction.
    let trapz;
    let (arg, code) = match func.dfg[inst] {
        ir::InstructionData::CondTrap { opcode, arg, code } => {
            // We want to branch *over* an unconditional trap.
            trapz = match opcode {
                ir::Opcode::Trapz => true,
                ir::Opcode::Trapnz => false,
                _ => panic!("Expected cond trap: {}", func.dfg.display_inst(inst, None)),
            };
            (arg, code)
        }
        _ => panic!("Expected cond trap: {}", func.dfg.display_inst(inst, None)),
    };

    // Split the EBB after `inst`:
    //
    //     trapnz arg
    //
    // Becomes:
    //
    //     brz arg, new_ebb
    //     trap
    //   new_ebb:
    //
    let old_ebb = func.layout.pp_ebb(inst);
    let new_ebb = func.dfg.make_ebb();
    if trapz {
        func.dfg.replace(inst).brnz(arg, new_ebb, &[]);
    } else {
        func.dfg.replace(inst).brz(arg, new_ebb, &[]);
    }

    let mut pos = FuncCursor::new(func).after_inst(inst);
    pos.use_srcloc(inst);
    pos.ins().trap(code);
    pos.insert_ebb(new_ebb);

    // Finally update the CFG.
    cfg.recompute_ebb(pos.func, old_ebb);
    cfg.recompute_ebb(pos.func, new_ebb);
}

/// Jump tables.
fn expand_br_table(
    inst: ir::Inst,
    func: &mut ir::Function,
    cfg: &mut ControlFlowGraph,
    isa: &dyn TargetIsa,
) {
    if isa.flags().jump_tables_enabled() {
        expand_br_table_jt(inst, func, cfg, isa);
    } else {
        expand_br_table_conds(inst, func, cfg, isa);
    }
}

/// Expand br_table to jump table.
fn expand_br_table_jt(
    inst: ir::Inst,
    func: &mut ir::Function,
    cfg: &mut ControlFlowGraph,
    isa: &dyn TargetIsa,
) {
    use crate::ir::condcodes::IntCC;

    let (arg, default_ebb, table) = match func.dfg[inst] {
        ir::InstructionData::BranchTable {
            opcode: ir::Opcode::BrTable,
            arg,
            destination,
            table,
        } => (arg, destination, table),
        _ => panic!("Expected br_table: {}", func.dfg.display_inst(inst, None)),
    };

    let table_size = func.jump_tables[table].len();
    let addr_ty = isa.pointer_type();
    let entry_ty = I32;

    let mut pos = FuncCursor::new(func).at_inst(inst);
    pos.use_srcloc(inst);

    // Bounds check
    let oob = pos
        .ins()
        .icmp_imm(IntCC::UnsignedGreaterThanOrEqual, arg, table_size as i64);

    pos.ins().brnz(oob, default_ebb, &[]);

    let base_addr = pos.ins().jump_table_base(addr_ty, table);
    let entry = pos
        .ins()
        .jump_table_entry(addr_ty, arg, base_addr, entry_ty.bytes() as u8, table);

    let addr = pos.ins().iadd(base_addr, entry);
    pos.ins().indirect_jump_table_br(addr, table);

    let ebb = pos.current_ebb().unwrap();
    pos.remove_inst();
    cfg.recompute_ebb(pos.func, ebb);
}

/// Expand br_table to series of conditionals.
fn expand_br_table_conds(
    inst: ir::Inst,
    func: &mut ir::Function,
    cfg: &mut ControlFlowGraph,
    _isa: &dyn TargetIsa,
) {
    use crate::ir::condcodes::IntCC;

    let (arg, default_ebb, table) = match func.dfg[inst] {
        ir::InstructionData::BranchTable {
            opcode: ir::Opcode::BrTable,
            arg,
            destination,
            table,
        } => (arg, destination, table),
        _ => panic!("Expected br_table: {}", func.dfg.display_inst(inst, None)),
    };

    // This is a poor man's jump table using just a sequence of conditional branches.
    let table_size = func.jump_tables[table].len();
    let mut pos = FuncCursor::new(func).at_inst(inst);
    pos.use_srcloc(inst);

    for i in 0..table_size {
        let dest = pos.func.jump_tables[table].as_slice()[i];
        let t = pos.ins().icmp_imm(IntCC::Equal, arg, i as i64);
        pos.ins().brnz(t, dest, &[]);
    }

    // `br_table` jumps to the default destination if nothing matches
    pos.ins().jump(default_ebb, &[]);

    let ebb = pos.current_ebb().unwrap();
    pos.remove_inst();
    cfg.recompute_ebb(pos.func, ebb);
}

/// Expand the select instruction.
///
/// Conditional moves are available in some ISAs for some register classes. The remaining selects
/// are handled by a branch.
fn expand_select(
    inst: ir::Inst,
    func: &mut ir::Function,
    cfg: &mut ControlFlowGraph,
    _isa: &dyn TargetIsa,
) {
    let (ctrl, tval, fval) = match func.dfg[inst] {
        ir::InstructionData::Ternary {
            opcode: ir::Opcode::Select,
            args,
        } => (args[0], args[1], args[2]),
        _ => panic!("Expected select: {}", func.dfg.display_inst(inst, None)),
    };

    // Replace `result = select ctrl, tval, fval` with:
    //
    //   brnz ctrl, new_ebb(tval)
    //   jump new_ebb(fval)
    // new_ebb(result):
    let old_ebb = func.layout.pp_ebb(inst);
    let result = func.dfg.first_result(inst);
    func.dfg.clear_results(inst);
    let new_ebb = func.dfg.make_ebb();
    func.dfg.attach_ebb_param(new_ebb, result);

    func.dfg.replace(inst).brnz(ctrl, new_ebb, &[tval]);
    let mut pos = FuncCursor::new(func).after_inst(inst);
    pos.use_srcloc(inst);
    pos.ins().jump(new_ebb, &[fval]);
    pos.insert_ebb(new_ebb);

    cfg.recompute_ebb(pos.func, new_ebb);
    cfg.recompute_ebb(pos.func, old_ebb);
}

fn expand_br_icmp(
    inst: ir::Inst,
    func: &mut ir::Function,
    cfg: &mut ControlFlowGraph,
    _isa: &dyn TargetIsa,
) {
    let (cond, a, b, destination, ebb_args) = match func.dfg[inst] {
        ir::InstructionData::BranchIcmp {
            cond,
            destination,
            ref args,
            ..
        } => (
            cond,
            args.get(0, &func.dfg.value_lists).unwrap(),
            args.get(1, &func.dfg.value_lists).unwrap(),
            destination,
            args.as_slice(&func.dfg.value_lists)[2..].to_vec(),
        ),
        _ => panic!("Expected br_icmp {}", func.dfg.display_inst(inst, None)),
    };

    let old_ebb = func.layout.pp_ebb(inst);
    func.dfg.clear_results(inst);

    let icmp_res = func.dfg.replace(inst).icmp(cond, a, b);
    let mut pos = FuncCursor::new(func).after_inst(inst);
    pos.use_srcloc(inst);
    pos.ins().brnz(icmp_res, destination, &ebb_args);

    cfg.recompute_ebb(pos.func, destination);
    cfg.recompute_ebb(pos.func, old_ebb);
}

/// Expand illegal `f32const` and `f64const` instructions.
fn expand_fconst(
    inst: ir::Inst,
    func: &mut ir::Function,
    _cfg: &mut ControlFlowGraph,
    _isa: &dyn TargetIsa,
) {
    let ty = func.dfg.value_type(func.dfg.first_result(inst));
    debug_assert!(!ty.is_vector(), "Only scalar fconst supported: {}", ty);

    // In the future, we may want to generate constant pool entries for these constants, but for
    // now use an `iconst` and a bit cast.
    let mut pos = FuncCursor::new(func).at_inst(inst);
    pos.use_srcloc(inst);
    let ival = match pos.func.dfg[inst] {
        ir::InstructionData::UnaryIeee32 {
            opcode: ir::Opcode::F32const,
            imm,
        } => pos.ins().iconst(ir::types::I32, i64::from(imm.bits())),
        ir::InstructionData::UnaryIeee64 {
            opcode: ir::Opcode::F64const,
            imm,
        } => pos.ins().iconst(ir::types::I64, imm.bits() as i64),
        _ => panic!("Expected fconst: {}", pos.func.dfg.display_inst(inst, None)),
    };
    pos.func.dfg.replace(inst).bitcast(ty, ival);
}

/// Expand illegal `stack_load` instructions.
fn expand_stack_load(
    inst: ir::Inst,
    func: &mut ir::Function,
    _cfg: &mut ControlFlowGraph,
    isa: &dyn TargetIsa,
) {
    let ty = func.dfg.value_type(func.dfg.first_result(inst));
    let addr_ty = isa.pointer_type();

    let mut pos = FuncCursor::new(func).at_inst(inst);
    pos.use_srcloc(inst);

    let (stack_slot, offset) = match pos.func.dfg[inst] {
        ir::InstructionData::StackLoad {
            opcode: _opcode,
            stack_slot,
            offset,
        } => (stack_slot, offset),
        _ => panic!(
            "Expected stack_load: {}",
            pos.func.dfg.display_inst(inst, None)
        ),
    };

    let addr = pos.ins().stack_addr(addr_ty, stack_slot, offset);

    // Stack slots are required to be accessible and aligned.
    let mflags = MemFlags::trusted();
    pos.func.dfg.replace(inst).load(ty, mflags, addr, 0);
}

/// Expand illegal `stack_store` instructions.
fn expand_stack_store(
    inst: ir::Inst,
    func: &mut ir::Function,
    _cfg: &mut ControlFlowGraph,
    isa: &dyn TargetIsa,
) {
    let addr_ty = isa.pointer_type();

    let mut pos = FuncCursor::new(func).at_inst(inst);
    pos.use_srcloc(inst);

    let (val, stack_slot, offset) = match pos.func.dfg[inst] {
        ir::InstructionData::StackStore {
            opcode: _opcode,
            arg,
            stack_slot,
            offset,
        } => (arg, stack_slot, offset),
        _ => panic!(
            "Expected stack_store: {}",
            pos.func.dfg.display_inst(inst, None)
        ),
    };

    let addr = pos.ins().stack_addr(addr_ty, stack_slot, offset);

    let mut mflags = MemFlags::new();
    // Stack slots are required to be accessible and aligned.
    mflags.set_notrap();
    mflags.set_aligned();
    pos.func.dfg.replace(inst).store(mflags, val, addr, 0);
}