These two new invariants eliminate corner cases which caused bugs if optimization didn't handle them.
Also, it will significantly simplify lifetime completion.
The implementation basically consists of these changes:
* add a flag in SILFunction which tells optimization if they need to take care of infinite loops
* add a utility to break infinite loops
* let all optimizations remove unreachable blocks and break infinite loops if necessary
* add verification to check the new SIL invariants
The new `breakIfniniteLoops` utility breaks infinite loops in the control flow by inserting an "artificial" loop exit to a new dead-end block with an `unreachable`.
It inserts a `cond_br` with a `builtin "infinite_loop_true_condition"`:
```
bb0:
br bb1
bb1:
br bb1 // back-end branch
```
->
```
bb0:
br bb1
bb1:
%1 = builtin "infinite_loop_true_condition"() // always true, but the compiler doesn't know
cond_br %1, bb2, bb3
bb2: // new back-end block
br bb1
bb3: // new dead-end block
unreachable
```
os log APIs, based on the fact that there is already a Sema check for
enforcing the user model.
Suppress the errors generated by for the _globalStringTablePointerBuiltin
when the OSLogOptimization pass emits diagnostics. This elimiantes the
cryptic error that always accompanies the diagnostics emitted by the
OSLogOptimization pass.
module to contain only code necessary for testing the compiler
optimizations and diagnostics. This commit comprises the following changes:
1. Rename the OSLogPrototype module to OSLogTestHelper and rename the files.
2. Make the private module: OSLogTestHelper independent of os overlay.
3. Simplify the os log test suites and make them not perform logging.
4. Enable the os log test suites on all platforms.
<rdar://problem/60542172>
