[llvm] [Codegen] Remove redundant instruction using machinelateCleanup (PR #139716)

[Jay Foad via llvm-commits]

================
@@ -189,7 +189,13 @@ static bool isCandidate(const MachineInstr *MI, Register &DefedReg,
       if (MO.isDef()) {
         if (i == 0 && !MO.isImplicit() && !MO.isDead())
           DefedReg = MO.getReg();
----------------
jayfoad wrote:

I'd appreciate some comments to explain what's going on, for the existing cases and the new cases. Example:
// If the first def is explicit and not dead, remember it.
I'm not sure why explicit matters here.

https://github.com/llvm/llvm-project/pull/139716