cmd/compile: remove needwritebarrier from the frontend
The write barrier insertion has moved to the SSA backend's
writebarrier pass. There is still needwritebarrier function
left in the frontend. This function is used in two places:
- fncall, which is called in ascompatet, which is called in
walking OAS2FUNC. For OAS2FUNC, in order pass we've already
created temporaries, and there is no write barrier for the
assignments of these temporaries.
- updateHasCall, which updates the HasCall flag of a node. the
HasCall flag is then used in
- fncall, mentioned above.
- ascompatet. As mentioned above, this is an assignment to
a temporary, no write barrier.
- reorder1, which is always called with a list produced by
ascompatte, which is a list of assignments to stack, which
have no write barrier.
- vmatch1, which is called in oaslit with r.Op as OSTRUCTLIT,
OARRAYLIT, OSLICELIT, or OMAPLIT. There is no write barrier
in those literals.
Therefore, the needwritebarrier function is unnecessary. This
CL removes it.