[llvm] [MISched] Unify the way to specify scheduling direction (PR #119518)

[David Green via llvm-commits]

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@@ -99,8 +99,16 @@
 
 namespace llvm {
 
-extern cl::opt<bool> ForceTopDown;
-extern cl::opt<bool> ForceBottomUp;
+namespace MISched {
+enum Direction {
+  Unspecified,
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davemgreen wrote:

Yeah I see, that makes sense. I don't have a strong opinion but would be temped to go that route and make it more explicit. The shuffler, whilst not the most important, seems to be assuming the default is Bidirectional where as the scheduler defaults to BottomUp. I have the feeling that MISched::Direction could get used more in the future, and if it does having an Unspecified makes it more awkward to rely upon.

Either way this LGTM. It's a nice cleanup.

https://github.com/llvm/llvm-project/pull/119518