rustc: When landing pads are off, avoid skipping cleanup code.

This forces various things to be created (e.g. drop glue), and also
happens to be necessary for GC liveness to recognize cleanups as
roots.

Author: Elliott Slaughter

src/rustc/middle/trans/base.rs

@@ -1233,8 +1233,12 @@ fn lazily_emit_tydesc_glue(ccx: @crate_ctxt, field: uint,
 fn call_tydesc_glue_full(++bcx: block, v: ValueRef, tydesc: ValueRef,
                          field: uint, static_ti: Option<@tydesc_info>) {
     let _icx = bcx.insn_ctxt("call_tydesc_glue_full");
-        if bcx.unreachable { return; }
     let ccx = bcx.ccx();
+    // NB: Don't short-circuit even if this block is unreachable because
+    // GC-based cleanup needs to the see that the roots are live.
+    let no_lpads =
+        ccx.sess.opts.debugging_opts & session::no_landing_pads != 0;
+    if bcx.unreachable && !no_lpads { return; }
 
     let static_glue_fn = match static_ti {
       None => None,
@@ -4510,7 +4514,11 @@ fn trans_block_cleanups_(bcx: block,
                          /* cleanup_cx: block, */ is_lpad: bool) ->
    block {
     let _icx = bcx.insn_ctxt("trans_block_cleanups");
-    if bcx.unreachable { return bcx; }
+    // NB: Don't short-circuit even if this block is unreachable because
+    // GC-based cleanup needs to the see that the roots are live.
+    let no_lpads =
+        bcx.ccx().sess.opts.debugging_opts & session::no_landing_pads != 0;
+    if bcx.unreachable && !no_lpads { return bcx; }
     let mut bcx = bcx;
     do vec::riter(cleanups) |cu| {
             match cu {