swift234

[Global Opt] update SILGlobalOpt to use static initializer if possible.

Update SILGlobalOpt to remove "once" call from addressor and set the
InitializerF for SILGlboalVariable if legal.

For calls to addressor in non-cold block, we check the addressor to find out
the globalinit_func and the associated SILGlobalVariable. If legal, we set
InitializerF of SILGlobalVariable and remove "once" call from addressor.

The current rules for legality:
1> the addressor contains a single "once" call
2> it calls globalinit_func
3> the globalinit_func is called by "once" from a single location
4> the globalinit_func is trivial

Update IRGen to emit llvm.global_ctors for global variables with static
initializers (i.e non-null InitializerF).

Performance --------
After:
Totals,54,67202,67202,67202,0,0 Onone
Totals,54,88948,88948,88948,0,0 O
Totals,54,71222,71222,71222,0,0 Ounchecked
Totals,54,66405,66405,66405,0,0 Onone
Totals,54,88759,88759,88759,0,0 O
Totals,54,71761,71761,71761,0,0 Ounchecked
Before:
Totals,55,68133,68133,68133,0,0 Onone
Totals,55,92458,92458,92458,0,0 O
Totals,55,72262,72262,72262,0,0 Ounchecked
Totals,55,69022,69022,69022,0,0 Onone
Totals,55,92178,92178,92178,0,0 O
Totals,55,72593,72593,72593,0,0 Ounchecked


Swift SVN r21996