Consider:

int test(unsigned short X, short Y) { return X+Y; }

$ llvm-gcc t.c -c -emit-llvm -o - -O3 | llc -march=c
signed int test(signed short ltmp_0_1, signed short ltmp_1_1) {
  return ((((signed int )(signed short )ltmp_1_1)) + (((unsigned int )(unsigned short )ltmp_0_1)));
}

The first argument should be unsigned.  This is a serious bug, because it means that bugpoint will get 
confused more often than it currently does.

-Chris