[llvm] [MachineCombiner][NFC] Split target-dependent patterns (PR #87991)

[Min-Yih Hsu via llvm-commits]

================
@@ -16,170 +16,24 @@
 
 namespace llvm {
 
+/// The combiner's goal may differ based on which pattern it is attempting
+/// to optimize.
+enum class CombinerObjective {
+  MustReduceDepth,            // The data dependency chain must be improved.
+  MustReduceRegisterPressure, // The register pressure must be reduced.
+  Default                     // The critical path must not be lengthened.
+};
+
 /// These are instruction patterns matched by the machine combiner pass.
-enum class MachineCombinerPattern {
+enum MachineCombinerPattern {
----------------
mshockwave wrote:

could we explicitly designate the underlying type here, like `enum MachineCombinerPattern : unsigned`

https://github.com/llvm/llvm-project/pull/87991