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gc: compile s == "" as len(s) == 0

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R=ken2
CC=golang-dev
https://golang.org/cl/840043
This commit is contained in:
Russ Cox 2010-04-11 15:24:44 -07:00
parent 9475cafa73
commit c9293f0cc7
1 changed files with 24 additions and 0 deletions
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24
src/cmd/gc/walk.c
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@ -1053,6 +1053,30 @@ walkexpr(Node **np, NodeList **init)
goto ret;
case OCMPSTR:
// If one argument to the comparison is an empty string,
// comparing the lengths instead will yield the same result
// without the function call.
if((isconst(n->left, CTSTR) && n->left->val.u.sval->len == 0) ||
(isconst(n->right, CTSTR) && n->right->val.u.sval->len == 0)) {
r = nod(n->etype, nod(OLEN, n->left, N), nod(OLEN, n->right, N));
typecheck(&r, Erv);
walkexpr(&r, init);
n = r;
goto ret;
}
// s + "badgerbadgerbadger" == "badgerbadgerbadger"
if((n->etype == OEQ || n->etype == ONE) &&
isconst(n->right, CTSTR) &&
n->left->op == OADDSTR && isconst(n->left->right, CTSTR) &&
cmpslit(n->right, n->left->right) == 0) {
r = nod(n->etype, nod(OLEN, n->left->left, N), nodintconst(0));
typecheck(&r, Erv);
walkexpr(&r, init);
n = r;
goto ret;
}
// sys_cmpstring(s1, s2) :: 0
r = mkcall("cmpstring", types[TINT], init,
conv(n->left, types[TSTRING]),