Conditional jump or move depends on uninitialized value in rustc

[brson]

Running make stage2/std.o VALGRIND_COMPILE=1 on Linux reports the following:

==15459== Conditional jump or move depends on uninitialised value(s)
==15459==    at 0x80DA7CD: _rust_fn960_middle_ty_ty_to_str (in /home/brian/Dev/rust/build/stage1/rustc)
==15459==    by 0x8072DA6: _rust_fn730_middle_trans_make_scalar_cmp_glue (in /home/brian/Dev/rust/build/stage1/rustc)
==15459==    by 0x80709E0: _rust_fn728_middle_trans_make_cmp_glue (in /home/brian/Dev/rust/build/stage1/rustc)
==15459==    by 0x806C938: _rust_fn715_middle_trans_make_generic_glue (in /home/brian/Dev/rust/build/stage1/rustc)
==15459==    by 0x807CA3E: _rust_fn747_middle_trans_lazily_emit_tydesc_glue (in /home/brian/Dev/rust/build/stage1/rustc)
==15459==    by 0x807E196: _rust_fn751_middle_trans_call_cmp_glue (in /home/brian/Dev/rust/build/stage1/rustc)
==15459==    by 0x8072603: _rust_fn729_middle_trans_make_cmp_glue_inner (in /home/brian/Dev/rust/build/stage1/rustc)
==15459==    by 0x83651CE: _rust_thunk3515_middle_trans_make_cmp_glue (in /home/brian/Dev/rust/build/stage1/rustc)
==15459==    by 0x807584E: _rust_fn738_middle_trans_iter_structural_ty_full (in /home/brian/Dev/rust/build/stage1/rustc)
==15459==    by 0x807163C: _rust_fn728_middle_trans_make_cmp_glue (in /home/brian/Dev/rust/build/stage1/rustc)
==15459==    by 0x806C938: _rust_fn715_middle_trans_make_generic_glue (in /home/brian/Dev/rust/build/stage1/rustc)
==15459==    by 0x807CA3E: _rust_fn747_middle_trans_lazily_emit_tydesc_glue (in /home/brian/Dev/rust/build/stage1/rustc)

I believe this test case reproduces the issue although the error manifests in a different way (it reproduces something!):

use std;
import std::option;
import std::option::none;

tag sty {
    ty_nil;
}

type raw_t = rec(sty struct,
                 option::t[str] cname,
                 uint hash);

fn mk_raw_ty(sty st, &option::t[str] cname) -> raw_t {
  ret rec(struct=st,
          cname=cname,
          hash=0u);
}

fn main() {
  mk_raw_ty(ty_nil, none[str]);
}

On the test case valgrind reports:

==15590== Conditional jump or move depends on uninitialised value(s)
==15590==    at 0x80496C3: _rust_fn1_mk_raw_ty (in /home/brian/Dev/rust/build/test/run-pass/compare.stage1)
==15590==    by 0x8049743: _rust_fn2_main (in /home/brian/Dev/rust/build/test/run-pass/compare.stage1)
==15590==    by 0x804945E: rust_exit_task_glue (in /home/brian/Dev/rust/build/test/run-pass/compare.stage1)

It seems to be related to the alias parameter, but changing just about anything in the test case makes the bug go into hiding.

[brson]

Checked in the test case as run-pass/alias-uninit-value.rs in ec30c71