auto merge of #8041 : dotdash/rust/const_if_else, r=huonw
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commit
544ef6cf35
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@ -850,6 +850,12 @@ pub fn const_get_elt(cx: &CrateContext, v: ValueRef, us: &[c_uint])
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}
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}
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pub fn is_const(v: ValueRef) -> bool {
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unsafe {
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llvm::LLVMIsConstant(v) == True
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}
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}
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pub fn const_to_int(v: ValueRef) -> c_longlong {
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unsafe {
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llvm::LLVMConstIntGetSExtValue(v)
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@ -65,44 +65,36 @@ pub fn trans_if(bcx: @mut Block,
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let _icx = push_ctxt("trans_if");
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match cond.node {
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// `if true` and `if false` can be trans'd more efficiently,
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// by dropping branches that are known to be impossible.
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ast::expr_lit(@ref l) => match l.node {
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ast::lit_bool(true) => {
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// if true { .. } [else { .. }]
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let then_bcx_in = scope_block(bcx, thn.info(), "if_true_then");
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let then_bcx_out = trans_block(then_bcx_in, thn, dest);
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let then_bcx_out = trans_block_cleanups(then_bcx_out,
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block_cleanups(then_bcx_in));
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Br(bcx, then_bcx_in.llbb);
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return then_bcx_out;
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}
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ast::lit_bool(false) => {
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match els {
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// if false { .. } else { .. }
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Some(elexpr) => {
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let (else_bcx_in, else_bcx_out) =
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trans_if_else(bcx, elexpr, dest, "if_false_else");
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Br(bcx, else_bcx_in.llbb);
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return else_bcx_out;
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}
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// if false { .. }
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None => return bcx,
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}
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}
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_ => {}
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},
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_ => {}
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}
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let Result {bcx, val: cond_val} =
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expr::trans_to_datum(bcx, cond).to_result();
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let then_bcx_in = scope_block(bcx, thn.info(), "then");
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let cond_val = bool_to_i1(bcx, cond_val);
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// Drop branches that are known to be impossible
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if is_const(cond_val) && !is_undef(cond_val) {
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if const_to_uint(cond_val) == 1 {
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// if true { .. } [else { .. }]
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return do with_scope(bcx, thn.info(), "if_true_then") |bcx| {
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let bcx_out = trans_block(bcx, thn, dest);
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trans_block_cleanups(bcx_out, block_cleanups(bcx))
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}
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} else {
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match els {
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// if false { .. } else { .. }
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Some(elexpr) => {
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return do with_scope(bcx, elexpr.info(), "if_false_then") |bcx| {
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let bcx_out = trans_if_else(bcx, elexpr, dest);
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trans_block_cleanups(bcx_out, block_cleanups(bcx))
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}
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}
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// if false { .. }
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None => return bcx,
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}
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}
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}
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let then_bcx_in = scope_block(bcx, thn.info(), "then");
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let then_bcx_out = trans_block(then_bcx_in, thn, dest);
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let then_bcx_out = trans_block_cleanups(then_bcx_out,
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block_cleanups(then_bcx_in));
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@ -113,7 +105,8 @@ pub fn trans_if(bcx: @mut Block,
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// 'else' context
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let (else_bcx_in, next_bcx) = match els {
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Some(elexpr) => {
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let (else_bcx_in, else_bcx_out) = trans_if_else(bcx, elexpr, dest, "else");
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let else_bcx_in = scope_block(bcx, elexpr.info(), "else");
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let else_bcx_out = trans_if_else(else_bcx_in, elexpr, dest);
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(else_bcx_in, join_blocks(bcx, [then_bcx_out, else_bcx_out]))
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}
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_ => {
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@ -131,9 +124,8 @@ pub fn trans_if(bcx: @mut Block,
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return next_bcx;
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// trans `else [ if { .. } ... | { .. } ]`
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fn trans_if_else(bcx: @mut Block, elexpr: @ast::expr,
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dest: expr::Dest, scope_name: &str) -> (@mut Block, @mut Block) {
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let else_bcx_in = scope_block(bcx, elexpr.info(), scope_name);
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fn trans_if_else(else_bcx_in: @mut Block, elexpr: @ast::expr,
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dest: expr::Dest) -> @mut Block {
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let else_bcx_out = match elexpr.node {
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ast::expr_if(_, _, _) => {
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let elseif_blk = ast_util::block_from_expr(elexpr);
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@ -143,11 +135,9 @@ pub fn trans_if(bcx: @mut Block,
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trans_block(else_bcx_in, blk, dest)
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}
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// would be nice to have a constraint on ifs
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_ => bcx.tcx().sess.bug("strange alternative in if")
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_ => else_bcx_in.tcx().sess.bug("strange alternative in if")
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};
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let else_bcx_out = trans_block_cleanups(else_bcx_out,
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block_cleanups(else_bcx_in));
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(else_bcx_in, else_bcx_out)
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trans_block_cleanups(else_bcx_out, block_cleanups(else_bcx_in))
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}
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}
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