* Simplified the logic for creating static initializers and constant folding for global variables: instead of creating a getter function, directly inline the constant value into the use-sites.
* Wired up the constant folder in GlobalOpt, so that a chains for global variables can be propagated, e.g.
let a = 1
let b = a + 10
let c = b + 5
* Fixed a problem where we didn't create a static initializer if a global is not used in the same module. E.g. a public let variable.
* Simplified the code in general.
rdar://problem/31515927
Mainly this is done for array literals.
This new optimization creates a statically initialized global variable which is the allocated object.
The alloc_ref instruction is replaced by a global_value instruction.
This optimization can give significant performance improvements for large array literals.
Static initializers are now represented by a list of literal and aggregate instructions in a SILGlobalVariable.
For details see SIL.rst.
This representation is cleaner than what we did so far (point to the initializer function and do some pattern matching).
One implication of that change is that now (a subset of) instructions not necessarily have a parent function.
Regarding the generated code it's a NFC.
Also the swift module format didn't change because so far we don't serializer global variables.
Strict aliasing only applies to memory operations that use strict
addresses. The optimizer needs to be aware of this flag. Uses of raw
addresses should not have their address substituted with a strict
address.
Also add Builtin.LoadRaw which will be used by raw pointer loads.
