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Avoid empty "else" blocks

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If an "if" expression has no "else", we don't have to create an LLVM
basic block either.
This commit is contained in:
Björn Steinbrink 2013-07-13 04:10:41 +02:00
parent 5df2bb1bcc
commit 1d2e1a9ae5
1 changed files with 21 additions and 14 deletions
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35
src/librustc/middle/trans/controlflow.rs
View file

@ -67,13 +67,8 @@ pub fn trans_if(bcx: block,
expr::trans_to_datum(bcx, cond).to_result();
let then_bcx_in = scope_block(bcx, thn.info(), "then");
let else_bcx_in = scope_block(bcx, els.info(), "else");
let cond_val = bool_to_i1(bcx, cond_val);
CondBr(bcx, cond_val, then_bcx_in.llbb, else_bcx_in.llbb);
debug!("then_bcx_in=%s, else_bcx_in=%s",
then_bcx_in.to_str(), else_bcx_in.to_str());
let then_bcx_out = trans_block(then_bcx_in, thn, dest);
let then_bcx_out = trans_block_cleanups(then_bcx_out,
@ -83,9 +78,10 @@ pub fn trans_if(bcx: block,
// because trans_expr will create another scope block
// context for the block, but we've already got the
// 'else' context
let else_bcx_out = match els {
let (else_bcx_in, next_bcx) = match els {
Some(elexpr) => {
match elexpr.node {
let else_bcx_in = scope_block(bcx, els.info(), "else");
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)
@ -95,14 +91,25 @@ pub fn trans_if(bcx: block,
}
// would be nice to have a constraint on ifs
_ => bcx.tcx().sess.bug("strange alternative in if")
}
}
_ => else_bcx_in
};
let else_bcx_out = trans_block_cleanups(else_bcx_out,
block_cleanups(else_bcx_in));
return join_blocks(bcx, [then_bcx_out, else_bcx_out]);
};
let else_bcx_out = trans_block_cleanups(else_bcx_out,
block_cleanups(else_bcx_in));
(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);
next_bcx
}
pub fn join_blocks(parent_bcx: block, in_cxs: &[block]) -> block {