rust/src/librustc/middle/trans/controlflow.rs

// Copyright 2012 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.


use back::link;
use lib;
use lib::llvm::*;
use middle::lang_items::{FailFnLangItem, FailBoundsCheckFnLangItem};
use middle::lang_items::LogTypeFnLangItem;
use middle::trans::base::*;
use middle::trans::build::*;
use middle::trans::callee;
use middle::trans::common::*;
use middle::trans::debuginfo;
use middle::trans::expr;
use middle::trans::type_of::*;
use middle::ty;
use util::common::indenter;
use util::ppaux;

use middle::trans::type_::Type;

use syntax::ast;
use syntax::ast::ident;
use syntax::ast_map::path_mod;
use syntax::ast_util;
use syntax::codemap::span;

pub fn trans_block(bcx: @mut Block, b: &ast::Block, dest: expr::Dest) -> @mut Block {
    let _icx = push_ctxt("trans_block");
    let mut bcx = bcx;
    for b.stmts.iter().advance |s| {
        debuginfo::update_source_pos(bcx, b.span);
        bcx = trans_stmt(bcx, *s);
    }
    match b.expr {
        Some(e) => {
            debuginfo::update_source_pos(bcx, e.span);
            bcx = expr::trans_into(bcx, e, dest);
        }
        None => {
            assert!(dest == expr::Ignore || bcx.unreachable);
        }
    }
    return bcx;
}

pub fn trans_if(bcx: @mut Block,
            cond: @ast::expr,
            thn: &ast::Block,
            els: Option<@ast::expr>,
            dest: expr::Dest)
         -> @mut Block {
    debug!("trans_if(bcx=%s, cond=%s, thn=%?, dest=%s)",
           bcx.to_str(), bcx.expr_to_str(cond), thn.id,
           dest.to_str(bcx.ccx()));
    let _indenter = indenter();

    let _icx = push_ctxt("trans_if");

    match cond.node {
        // `if true` and `if false` can be trans'd more efficiently,
        // by dropping branches that are known to be impossible.
        ast::expr_lit(@ref l) => match l.node {
            ast::lit_bool(true) => {
                // if true { .. } [else { .. }]
                let then_bcx_in = scope_block(bcx, thn.info(), "if_true_then");
                let then_bcx_out = trans_block(then_bcx_in, thn, dest);
                let then_bcx_out = trans_block_cleanups(then_bcx_out,
                                                        block_cleanups(then_bcx_in));
                Br(bcx, then_bcx_in.llbb);
                return then_bcx_out;
            }
            ast::lit_bool(false) => {
                match els {
                    // if false { .. } else { .. }
                    Some(elexpr) => {
                        let (else_bcx_in, else_bcx_out) =
                            trans_if_else(bcx, elexpr, dest, "if_false_else");
                        Br(bcx, else_bcx_in.llbb);
                        return else_bcx_out;
                    }
                    // if false { .. }
                    None => return bcx,
                }
            }
            _ => {}
        },
        _ => {}
    }

    let Result {bcx, val: cond_val} =
        expr::trans_to_datum(bcx, cond).to_result();

    let then_bcx_in = scope_block(bcx, thn.info(), "then");

    let cond_val = bool_to_i1(bcx, cond_val);

    let then_bcx_out = trans_block(then_bcx_in, thn, dest);
    let then_bcx_out = trans_block_cleanups(then_bcx_out,
                                            block_cleanups(then_bcx_in));

    // Calling trans_block directly instead of trans_expr
    // because trans_expr will create another scope block
    // context for the block, but we've already got the
    // 'else' context
    let (else_bcx_in, next_bcx) = match els {
      Some(elexpr) => {
          let (else_bcx_in, else_bcx_out) = trans_if_else(bcx, elexpr, dest, "else");
          (else_bcx_in, join_blocks(bcx, [then_bcx_out, else_bcx_out]))
      }
      _ => {
          let next_bcx = sub_block(bcx, "next");
          Br(then_bcx_out, next_bcx.llbb);

          (next_bcx, next_bcx)
      }
    };

    debug!("then_bcx_in=%s, else_bcx_in=%s",
           then_bcx_in.to_str(), else_bcx_in.to_str());

    CondBr(bcx, cond_val, then_bcx_in.llbb, else_bcx_in.llbb);
    return next_bcx;

    // trans `else [ if { .. } ... | { .. } ]`
    fn trans_if_else(bcx: @mut Block, elexpr: @ast::expr,
                     dest: expr::Dest, scope_name: &str) -> (@mut Block, @mut Block) {
        let else_bcx_in = scope_block(bcx, elexpr.info(), scope_name);
        let else_bcx_out = match elexpr.node {
            ast::expr_if(_, _, _) => {
                let elseif_blk = ast_util::block_from_expr(elexpr);
                trans_block(else_bcx_in, &elseif_blk, dest)
            }
            ast::expr_block(ref blk) => {
                trans_block(else_bcx_in, blk, dest)
            }
            // would be nice to have a constraint on ifs
            _ => bcx.tcx().sess.bug("strange alternative in if")
        };
        let else_bcx_out = trans_block_cleanups(else_bcx_out,
                                                block_cleanups(else_bcx_in));
        (else_bcx_in, else_bcx_out)
    }
}

pub fn join_blocks(parent_bcx: @mut Block, in_cxs: &[@mut Block]) -> @mut Block {
    let out = sub_block(parent_bcx, "join");
    let mut reachable = false;
    for in_cxs.iter().advance |bcx| {
        if !bcx.unreachable {
            Br(*bcx, out.llbb);
            reachable = true;
        }
    }
    if !reachable {
        Unreachable(out);
    }
    return out;
}

pub fn trans_while(bcx: @mut Block, cond: @ast::expr, body: &ast::Block) -> @mut Block {
    let _icx = push_ctxt("trans_while");
    let next_bcx = sub_block(bcx, "while next");

    //            bcx
    //             |
    //          loop_bcx
    //             |
    //         cond_bcx_in  <--------+
    //             |                 |
    //         cond_bcx_out          |
    //           |      |            |
    //           |    body_bcx_in    |
    //    +------+      |            |
    //    |           body_bcx_out --+
    // next_bcx

    let loop_bcx = loop_scope_block(bcx, next_bcx, None, "`while`",
                                    body.info());
    let cond_bcx_in = scope_block(loop_bcx, cond.info(), "while loop cond");
    let body_bcx_in = scope_block(loop_bcx, body.info(), "while loop body");
    Br(bcx, loop_bcx.llbb);
    Br(loop_bcx, cond_bcx_in.llbb);

    // compile the condition
    let Result {bcx: cond_bcx_out, val: cond_val} =
        expr::trans_to_datum(cond_bcx_in, cond).to_result();
    let cond_val = bool_to_i1(cond_bcx_out, cond_val);
    let cond_bcx_out =
        trans_block_cleanups(cond_bcx_out, block_cleanups(cond_bcx_in));
    CondBr(cond_bcx_out, cond_val, body_bcx_in.llbb, next_bcx.llbb);

    // loop body:
    let body_bcx_out = trans_block(body_bcx_in, body, expr::Ignore);
    cleanup_and_Br(body_bcx_out, body_bcx_in, cond_bcx_in.llbb);

    return next_bcx;
}

pub fn trans_loop(bcx:@mut Block,
                  body: &ast::Block,
                  opt_label: Option<ident>)
               -> @mut Block {
    let _icx = push_ctxt("trans_loop");
    let next_bcx = sub_block(bcx, "next");
    let body_bcx_in = loop_scope_block(bcx, next_bcx, opt_label, "`loop`",
                                       body.info());
    Br(bcx, body_bcx_in.llbb);
    let body_bcx_out = trans_block(body_bcx_in, body, expr::Ignore);
    cleanup_and_Br(body_bcx_out, body_bcx_in, body_bcx_in.llbb);
    return next_bcx;
}

pub fn trans_log(log_ex: &ast::expr,
                 lvl: @ast::expr,
                 bcx: @mut Block,
                 e: @ast::expr) -> @mut Block {
    let _icx = push_ctxt("trans_log");
    let ccx = bcx.ccx();
    let mut bcx = bcx;
    if ty::type_is_bot(expr_ty(bcx, lvl)) {
       return expr::trans_into(bcx, lvl, expr::Ignore);
    }

    let (modpath, modname) = {
        let path = &mut bcx.fcx.path;
        let mut modpath = ~[path_mod(ccx.sess.ident_of(ccx.link_meta.name))];
        for path.iter().advance |e| {
            match *e {
                path_mod(_) => { modpath.push(*e) }
                _ => {}
            }
        }
        let modname = path_str(ccx.sess, modpath);
        (modpath, modname)
    };

    let global = if ccx.module_data.contains_key(&modname) {
        ccx.module_data.get_copy(&modname)
    } else {
        let s = link::mangle_internal_name_by_path_and_seq(
            ccx, modpath, "loglevel");
        let global;
        unsafe {
            global = do s.as_c_str |buf| {
                llvm::LLVMAddGlobal(ccx.llmod, Type::i32().to_ref(), buf)
            };
            llvm::LLVMSetGlobalConstant(global, False);
            llvm::LLVMSetInitializer(global, C_null(Type::i32()));
            lib::llvm::SetLinkage(global, lib::llvm::InternalLinkage);
        }
        ccx.module_data.insert(modname, global);
        global
    };
    let current_level = Load(bcx, global);
    let level = unpack_result!(bcx, {
        do with_scope_result(bcx, lvl.info(), "level") |bcx| {
            expr::trans_to_datum(bcx, lvl).to_result()
        }
    });

    let llenabled = ICmp(bcx, lib::llvm::IntUGE, current_level, level);
    do with_cond(bcx, llenabled) |bcx| {
        do with_scope(bcx, log_ex.info(), "log") |bcx| {
            let mut bcx = bcx;

            // Translate the value to be logged
            let val_datum = unpack_datum!(bcx, expr::trans_to_datum(bcx, e));

            // Call the polymorphic log function
            let val = val_datum.to_ref_llval(bcx);
            let did = langcall(bcx, Some(e.span), "", LogTypeFnLangItem);
            let bcx = callee::trans_lang_call_with_type_params(
                bcx, did, [level, val], [val_datum.ty], expr::Ignore);
            bcx
        }
    }
}

pub fn trans_break_cont(bcx: @mut Block,
                        opt_label: Option<ident>,
                        to_end: bool)
                     -> @mut Block {
    let _icx = push_ctxt("trans_break_cont");
    // Locate closest loop block, outputting cleanup as we go.
    let mut unwind = bcx;
    let mut cur_scope = unwind.scope;
    let mut target;
    loop {
        cur_scope = match cur_scope {
            Some(@ScopeInfo {
                loop_break: Some(brk),
                loop_label: l,
                parent,
                _
            }) => {
                // If we're looking for a labeled loop, check the label...
                target = if to_end {
                    brk
                } else {
                    unwind
                };
                match opt_label {
                    Some(desired) => match l {
                        Some(actual) if actual == desired => break,
                        // If it doesn't match the one we want,
                        // don't break
                        _ => parent,
                    },
                    None => break,
                }
            }
            Some(inf) => inf.parent,
            None => {
                unwind = match unwind.parent {
                    Some(bcx) => bcx,
                        // This is a return from a loop body block
                        None => {
                            Store(bcx, C_bool(!to_end), bcx.fcx.llretptr.get());
                            cleanup_and_leave(bcx, None, Some(bcx.fcx.get_llreturn()));
                            Unreachable(bcx);
                            return bcx;
                        }
                };
                unwind.scope
            }
        }
    }
    cleanup_and_Br(bcx, unwind, target.llbb);
    Unreachable(bcx);
    return bcx;
}

pub fn trans_break(bcx: @mut Block, label_opt: Option<ident>) -> @mut Block {
    return trans_break_cont(bcx, label_opt, true);
}

pub fn trans_cont(bcx: @mut Block, label_opt: Option<ident>) -> @mut Block {
    return trans_break_cont(bcx, label_opt, false);
}

pub fn trans_ret(bcx: @mut Block, e: Option<@ast::expr>) -> @mut Block {
    let _icx = push_ctxt("trans_ret");
    let mut bcx = bcx;
    let dest = match bcx.fcx.loop_ret {
      Some((flagptr, retptr)) => {
        // This is a loop body return. Must set continue flag (our retptr)
        // to false, return flag to true, and then store the value in the
        // parent's retptr.
        Store(bcx, C_bool(true), flagptr);
        Store(bcx, C_bool(false), bcx.fcx.llretptr.get());
        expr::SaveIn(match e {
          Some(x) => PointerCast(bcx, retptr,
                                 type_of(bcx.ccx(), expr_ty(bcx, x)).ptr_to()),
          None => retptr
        })
      }
      None => match bcx.fcx.llretptr {
        None => expr::Ignore,
        Some(retptr) => expr::SaveIn(retptr),
      }
    };
    match e {
      Some(x) => {
        bcx = expr::trans_into(bcx, x, dest);
      }
      _ => ()
    }
    cleanup_and_leave(bcx, None, Some(bcx.fcx.get_llreturn()));
    Unreachable(bcx);
    return bcx;
}

pub fn trans_fail_expr(bcx: @mut Block,
                       sp_opt: Option<span>,
                       fail_expr: Option<@ast::expr>)
                    -> @mut Block {
    let _icx = push_ctxt("trans_fail_expr");
    let mut bcx = bcx;
    match fail_expr {
        Some(arg_expr) => {
            let ccx = bcx.ccx();
            let tcx = ccx.tcx;
            let arg_datum = unpack_datum!(
                bcx, expr::trans_to_datum(bcx, arg_expr));

            if ty::type_is_str(arg_datum.ty) {
                let (lldata, _) = arg_datum.get_vec_base_and_len_no_root(bcx);
                return trans_fail_value(bcx, sp_opt, lldata);
            } else if bcx.unreachable || ty::type_is_bot(arg_datum.ty) {
                return bcx;
            } else {
                bcx.sess().span_bug(
                    arg_expr.span, ~"fail called with unsupported type " +
                    ppaux::ty_to_str(tcx, arg_datum.ty));
            }
        }
        _ => trans_fail(bcx, sp_opt, @"explicit failure")
    }
}

pub fn trans_fail(bcx: @mut Block,
                  sp_opt: Option<span>,
                  fail_str: @str)
               -> @mut Block {
    let _icx = push_ctxt("trans_fail");
    let V_fail_str = C_cstr(bcx.ccx(), fail_str);
    return trans_fail_value(bcx, sp_opt, V_fail_str);
}

fn trans_fail_value(bcx: @mut Block,
                    sp_opt: Option<span>,
                    V_fail_str: ValueRef)
                 -> @mut Block {
    let _icx = push_ctxt("trans_fail_value");
    let ccx = bcx.ccx();
    let (V_filename, V_line) = match sp_opt {
      Some(sp) => {
        let sess = bcx.sess();
        let loc = sess.parse_sess.cm.lookup_char_pos(sp.lo);
        (C_cstr(bcx.ccx(), loc.file.name),
         loc.line as int)
      }
      None => {
        (C_cstr(bcx.ccx(), @"<runtime>"), 0)
      }
    };
    let V_str = PointerCast(bcx, V_fail_str, Type::i8p());
    let V_filename = PointerCast(bcx, V_filename, Type::i8p());
    let args = ~[V_str, V_filename, C_int(ccx, V_line)];
    let did = langcall(bcx, sp_opt, "", FailFnLangItem);
    let bcx = callee::trans_lang_call(bcx, did, args, Some(expr::Ignore)).bcx;
    Unreachable(bcx);
    return bcx;
}

pub fn trans_fail_bounds_check(bcx: @mut Block, sp: span,
                               index: ValueRef, len: ValueRef) -> @mut Block {
    let _icx = push_ctxt("trans_fail_bounds_check");
    let (filename, line) = filename_and_line_num_from_span(bcx, sp);
    let args = ~[filename, line, index, len];
    let did = langcall(bcx, Some(sp), "", FailBoundsCheckFnLangItem);
    let bcx = callee::trans_lang_call(bcx, did, args, Some(expr::Ignore)).bcx;
    Unreachable(bcx);
    return bcx;
}