diff options
Diffstat (limited to 'src')
| -rw-r--r-- | src/librustc/middle/trans/controlflow.rs | 72 |
1 files changed, 55 insertions, 17 deletions
diff --git a/src/librustc/middle/trans/controlflow.rs b/src/librustc/middle/trans/controlflow.rs index e03a6e7c167..36f1f5cdbef 100644 --- a/src/librustc/middle/trans/controlflow.rs +++ b/src/librustc/middle/trans/controlflow.rs @@ -63,6 +63,38 @@ pub fn trans_if(bcx: block, 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(); @@ -80,22 +112,8 @@ pub fn trans_if(bcx: block, // 'else' context let (else_bcx_in, next_bcx) = match els { Some(elexpr) => { - 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) - } - 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, join_blocks(bcx, [then_bcx_out, else_bcx_out])) + 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"); @@ -109,7 +127,27 @@ pub fn trans_if(bcx: block, then_bcx_in.to_str(), else_bcx_in.to_str()); CondBr(bcx, cond_val, then_bcx_in.llbb, else_bcx_in.llbb); - next_bcx + return next_bcx; + + // trans `else [ if { .. } ... | { .. } ]` + fn trans_if_else(bcx: block, elexpr: @ast::expr, + dest: expr::Dest, scope_name: &str) -> (block, 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: block, in_cxs: &[block]) -> block { |