The NewDefault was used to simplify the updating of PHI nodes, but it
causes some inefficiency for target that will run structurizer later. For
example, for a simple two-case switch, the extra NewDefault is causing
unstructured CFG like:
O
/ \
O O
/ \ / \
C1 ND C2
\ | /
\ | /
D
The change is to avoid the ND(NewDefault) block, that is we will get a
structured CFG for above example like:
O
/ \
/ \
O O
/ \ / \
C1 \ / C2
\-> D <-/
The IR change introduced by this patch should be trivial to other targets,
so I am doing this unconditionally.
Fall-through among the cases will also cause unstructured CFG, but it need
more work and will be addressed in a separate change.
Reviewed by: arsenm
Differential Revision: https://reviews.llvm.org/D123607
1e01f95057