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Be a little more clever about picking columns to match on in trans_alt

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This should result in slightly more efficient matching of 'complex'
patterns with multiple discriminants in them.
This commit is contained in:
Marijn Haverbeke 2011-08-02 12:57:27 +02:00
parent f8fa574864
commit 6c9b90d06a
1 changed files with 34 additions and 4 deletions
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38
src/comp/middle/trans_alt.rs
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@ -228,7 +228,37 @@ fn any_box_pat(m: &match, col: uint) -> bool {
}
type exit_node = {bound: bind_map, from: BasicBlockRef, to: BasicBlockRef};
type mk_fail = fn() -> BasicBlockRef ;
type mk_fail = fn() -> BasicBlockRef;
fn pick_col(m: &match) -> uint {
let scores = ivec::init_elt_mut(0u, ivec::len(m.(0).pats));
for br: match_branch in m {
let i = 0u;
for p: @ast::pat in br.pats {
alt p.node {
ast::pat_lit(_) | ast::pat_tag(_, _) { scores.(i) += 1u; }
_ {}
}
i += 1u;
}
}
let max_score = 0u;
let best_col = 0u;
let i = 0u;
for score: uint in scores {
// Irrefutable columns always go first, they'd only be duplicated in
// the branches.
if score == 0u { ret i; }
// If no irrefutable ones are found, we pick the one with the biggest
// branching factor.
if score > max_score {
max_score = score;
best_col = i;
}
i += 1u;
}
ret best_col;
}
fn compile_submatch(bcx: @block_ctxt, m: &match, vals: ValueRef[],
f: &mk_fail, exits: &mutable exit_node[]) {
@ -239,10 +269,10 @@ fn compile_submatch(bcx: @block_ctxt, m: &match, vals: ValueRef[],
ret;
}
// FIXME maybe be clever about picking a column.
let col = 0u;
let col = pick_col(m);
let val = vals.(col);
let vals_left = ivec::slice(vals, 1u, ivec::len(vals));
let vals_left = ivec::slice(vals, 0u, col) +
ivec::slice(vals, col + 1u, ivec::len(vals));
let ccx = bcx.fcx.lcx.ccx;
let pat_id = 0;
for br: match_branch in m {