The XXOptUtils.h convention is already established and parallels
the SIL/XXUtils convention.
New:
- InstOptUtils.h
- CFGOptUtils.h
- BasicBlockOptUtils.h
- ValueLifetime.h
Removed:
- Local.h
- Two conflicting CFG.h files
This reorganization is helpful before I introduce more
utilities for block cloning similar to SinkAddressProjections.
Move the control flow utilies out of Local.h, which was an
unreadable, unprincipled mess. Rename it to InstOptUtils.h, and
confine it to small APIs for working with individual instructions.
These are the optimizer's additions to /SIL/InstUtils.h.
Rename CFG.h to CFGOptUtils.h and remove the one in /Analysis. Now
there is only SIL/CFG.h, resolving the naming conflict within the
swift project (this has always been a problem for source tools). Limit
this header to low-level APIs for working with branches and CFG edges.
Add BasicBlockOptUtils.h for block level transforms (it makes me sad
that I can't use BBOptUtils.h, but SIL already has
BasicBlockUtils.h). These are larger APIs for cloning or removing
whole blocks.
DestroyHoisting moves destroys of memory locations up the control flow as far as possible.
Beside destroy_addr, also "store [assign]" is considered a destroy, because is is equivalent to an destroy_addr + a "store [init]".
The main purpose of this optimization is to minimize copy-on-write operations for arrays, etc. Especially if such COW containers are used as enum payloads and modified in-place. E.g.
switch e {
case .A(var arr):
arr.append(x)
self = .A(arr)
...
In such a case DestroyHoisting can move the destroy of the self-assignment up before the switch and thus let the array buffer only be single-referenced at the time of the append.
When we have ownership SIL throughout the pass pipeline this optimization will replace the current destroy hoisting optimization in CopyForwarding.
For now, this optimization only runs in the mandatory pipeline (but not for -Onone) where we already have ownership SIL.
SR-10605
rdar://problem/50463362
