I'm trying to detect loops of the form
while (*x != y)
++x;
which mimic the behaviour of function rawmemchr. Note, the size of *x is not
necessarily one byte. Thus ultimately I would like to detect such loops and
replace them with calls to builtins rawmemchr8, rawmemchr16, rawmemchr32 if
they are implemented in the backend:
x = __builtin_rawmemchr16(x, y);
I'm wondering whether there is a particular place in order to detect such loop
patterns. For example, in the loop distribution pass GCC recognizes loops
which mimic the behavior of memset, memcpy, memmove and replaces them with
calls to their corresponding builtins, respectively. The pass and in
particular partitioning of statements depends on whether a statement is used
outside of a partition or not. This works perfectly fine for loops which
implement the mentioned mem* operations since their result is typically
ignored. However, the result of a rawmemchr function is/should never be
ignored. Therefore, such loops are currently recognized as having a reduction
which makes an implementation into the loop distribution pass not straight
forward to me.
Are there other places where you would detect such loops? Any comments?
Cheers,
Stefan
