SILOptimizer: a new phi-argument expansion optimization.
If only a single field of a struct phi-argument is used, replace the argument by the field value.
br bb(%str)
bb(%phi):
%f = struct_extract %phi, #Field // the only use of %phi
use %f
is replaced with
%f = struct_extract %str, #Field
br bb(%f)
bb(%phi):
use %phi
This also works if the phi-argument is in a def-use cycle.
The new PhiExpansionPass is in the same file as the RedundantPhiEliminationPass. Therefore I renamed the source file to PhiArgumentOptimizations.cpp
