SIL optimizer: consider non-branch terminators with a single successor for critical edges.

[eeckstein]

For example: a switch_enum for a single-case enum. It has only a single successor edge, but needs to be split as well (if the destination block has multiple predecessors).

Fixes a crash in SimplifyCFG.
rdar://problem/44675677

[eeckstein]

@swift-ci test

[eeckstein]

@swift-ci benchmark

[swift-ci]

Build comment file:

No performance and code size changes

How to read the data

The tables contain differences in performance which are larger than 8% and differences in code size which are larger than 1%.

If you see any unexpected regressions, you should consider fixing the regressions before you merge the PR.

Noise: Sometimes the performance results (not code size!) contain false alarms. Unexpected regressions which are marked with '(?)' are probably noise. If you see regressions which you cannot explain you can try to run the benchmarks again. If regressions still show up, please consult with the performance team (@eeckstein).

Hardware Overview

  Model Name: Mac Pro
  Model Identifier: MacPro6,1
  Processor Name: 12-Core Intel Xeon E5
  Processor Speed: 2.7 GHz
  Number of Processors: 1
  Total Number of Cores: 12
  L2 Cache (per Core): 256 KB
  L3 Cache: 30 MB
  Memory: 64 GB

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[atrick]

Yes, that makes sense. My working branch already verifies that only a Branch can jump to a block with multiple predecessors.