As noted in https://gcc.gnu.org/ml/gcc-patches/2014-02/msg01391.html
a bitmap-related cleanup turned add_used_regs_1 into a no-op for pseudo
registers, because the result of:
regno = reg_renumber[regno];
is never used. This patch does as Steven requested and adds an
assert that no allocated pseudos are seen here.
gcc/
* caller-save.c: Include rtl-iter.h.
(add_used_regs_1): Delete.
(add_used_regs): Use FOR_EACH_SUBRTX rather than for_each_rtx
to iterate over subrtxes. Assert that any remaining pseudos
have been spilled.