[BPF] fix sub-register handling for bpf_fastcall (#110618)

bpf_fastcall induced spill/fill pairs should be generated for
sub-register as well as for sub-registers. At the moment this is not the
case, e.g.:

    $ cat t.c
    extern int foo(void) __attribute__((bpf_fastcall));

    int bar(int a) {
      foo();
      return a;
    }

    $ clang --target=bpf -mcpu=v3 -O2 -S t.c -o -
    ...
    call foo
    w0 = w1
    exit

Modify BPFMIPeephole.cpp:collectBPFFastCalls() to check sub-registers
liveness and thus produce correct code for example above:

    *(u64 *)(r10 - 8) = r1
    call foo
    r1 = *(u64 *)(r10 - 8)
    w0 = w1
    exit

0 files changed, 0 insertions, 0 deletions