For example:
```
%0 = load %1
copy_addr %1 to %2
```
->
```
%0 = load %1
store %0 to %2
```
This is important for MandatoryRedundantLoadElimination to be able to create statically initialized globals in the mandatory pipeline.
For example:
```
public struct MyStruct {
public static let r: Range<Int> = 1 ..< 3
}
```
gets a statically initialized global, even at Onone, with this improvement.
rdar://149356742
PredictableMemoryAccessOptimizations has become unmaintainable as-is.
RedundantLoadElimination does (almost) the same thing as PredictableMemoryAccessOptimizations.
It's not as powerful but good enough because PredictableMemoryAccessOptimizations is actually only needed for promoting integer values for mandatory constant propagation.
And most importantly: RedundantLoadElimination does not insert additional copies which was a big problem in PredictableMemoryAccessOptimizations.
Fixes rdar://142814676
Find all the usages of `--enable-experimental-feature` or
`--enable-upcoming-feature` in the tests and replace some of the
`REQUIRES: asserts` to use `REQUIRES: swift-feature-Foo` instead, which
should correctly apply to depending on the asserts/noasserts mode of the
toolchain for each feature.
Remove some comments that talked about enabling asserts since they don't
apply anymore (but I might had miss some).
All this was done with an automated script, so some formatting weirdness
might happen, but I hope I fixed most of those.
There might be some tests that were `REQUIRES: asserts` that might run
in `noasserts` toolchains now. This will normally be because their
feature went from experimental to upcoming/base and the tests were not
updated.
As with the lexical flag, when creating an alloc_stack corresponding to
an alloc_box, transfer the var_decl flag from any begin_borrow users of
the box.
