[CodeGen] Turn MCRegUnit into an enum class (NFC) (#167943)

This changes `MCRegUnit` type from `unsigned` to `enum class : unsigned`
and inserts necessary casts.
The added `MCRegUnitToIndex` functor is used with `SparseSet`,
`SparseMultiSet` and `IndexedMap` in a few places.

`MCRegUnit` is opaque to users, so it didn't seem worth making it a
full-fledged class like `Register`.

Static type checking has detected one issue in
`PrologueEpilogueInserter.cpp`, where `BitVector` created for
`MCRegister` is indexed by both `MCRegister` and `MCRegUnit`.

The number of casts could be reduced by using `IndexedMap` in more
places and/or adding a `BitVector` adaptor, but the number of casts *per
file* is still small and `IndexedMap` has limitations, so it didn't seem
worth the effort.

Pull Request: https://github.com/llvm/llvm-project/pull/167943

1 files changed, 2 insertions, 2 deletions

diff --git a/llvm/lib/CodeGen/MachineCopyPropagation.cpp b/llvm/lib/CodeGen/MachineCopyPropagation.cpp
index 5ec7c48d7ee6..2a344b40c30c 100644
--- a/llvm/lib/CodeGen/MachineCopyPropagation.cpp
+++ b/llvm/lib/CodeGen/MachineCopyPropagation.cpp
@@ -138,7 +138,7 @@ public:
       for (unsigned SafeReg = 0, E = TRI.getNumRegs(); SafeReg < E; ++SafeReg)
         if (!RegMaskOp.clobbersPhysReg(SafeReg))
           for (MCRegUnit SafeUnit : TRI.regunits(SafeReg))
-            PreservedRegUnits.set(SafeUnit);
+            PreservedRegUnits.set(static_cast<unsigned>(SafeUnit));
 
       return PreservedRegUnits;
     }
@@ -996,7 +996,7 @@ void MachineCopyPropagation::ForwardCopyPropagateBlock(MachineBasicBlock &MBB) {
         // this register mask.
         bool MIRefedinCopyInfo = false;
         for (MCRegUnit RegUnit : TRI->regunits(Reg)) {
-          if (!PreservedRegUnits.test(RegUnit))
+          if (!PreservedRegUnits.test(static_cast<unsigned>(RegUnit)))
             Tracker.clobberRegUnit(RegUnit, *TRI, *TII, UseCopyInstr);
           else {
             if (MaybeDead == Tracker.findCopyForUnit(RegUnit, *TRI)) {