[PATCH] D127712: Prevent crash when TurnSwitchRangeIntoICmp receives default unreachable destination

[Samuel Eubanks via Phabricator via llvm-commits]

swamulism added inline comments.


================
Comment at: llvm/test/Transforms/SimplifyCFG/switch-default-undef.ll:9
+define void @0(i8 %sw, i32* %p0) {
+  switch i8 %sw, label %group3 [
+    i8 0, label %group1
----------------
hans wrote:
> In this switch, the default destination doesn't look unreachable. Is it made unreachable by some other transformation that happens before TurnSwitchRangeIntoICmp()? Can you make the test show the input that TurnSwitchRangeIntoICmp operates on directly?
It is made unreachable by some other transformation. 
Using the IR when the crash occurs in `TurnSwitchRangeIntoICmp()` as an input actually doesn't cause a crash (I assume it gets optimized out before we get here). 
So, I guess there is some other combination of transformations that causes `TurnSwitchRangeIntoICmp()` to get a switch looking like this:
```
  switch i8 %sw, label %unreachable [
    i8 10, label %group2
    i8 9, label %group2
  ]
```


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D127712/new/

https://reviews.llvm.org/D127712