[llvm] [SystemZ] Drop regstate of SELRMux operand in selectSLRMux(). (PR #128555)

[Ulrich Weigand via llvm-commits]

================
@@ -114,7 +114,7 @@ void SystemZPostRewrite::selectSELRMux(MachineBasicBlock &MBB,
   if (Src1Reg == Src2Reg) {
     BuildMI(*MBBI->getParent(), MBBI, MBBI->getDebugLoc(),
             TII->get(SystemZ::COPY), DestReg)
-        .addReg(MBBI->getOperand(1).getReg(), getRegState(MBBI->getOperand(1)));
+        .addReg(MBBI->getOperand(1).getReg(), RegState::Renamable);
----------------
uweigand wrote:

Hard-coding the renamable looks odd to me.  It may be correct now, but who knows what's going on after possible future changes?

Since the same register is present as both source operands, but with differing regstate flags, can't we simply use the *intersection* of the flags from the two operands here?

https://github.com/llvm/llvm-project/pull/128555