[AMDGPU] Return better Changed status from SIOptimizeExecMasking

[piotr]

LGTM

llvm/lib/Target/AMDGPU/SIOptimizeExecMasking.cpp

bool SIOptimizeExecMasking::runOnMachineFunction(MachineFunction &MF) {
   //
   //     x = copy exec
   //     z = s_<op>_b64 x, y
   //     exec = copy z
   // =>
   //     x = s_<op>_saveexec_b64 y
   //
 
+  bool Changed = false;
   for (MachineBasicBlock &MBB : MF) {
     MachineBasicBlock::reverse_iterator I = fixTerminators(*TII, MBB);
     MachineBasicBlock::reverse_iterator E = MBB.rend();
     if (I == E)
       continue;
 
     // It's possible to see other terminator copies after the exec copy. This
     // can happen if control flow pseudos had their outputs used by phis.
if (CopyFromExecInst == E) {
           isLogicalOpOnExec(*PrepareExecInst) == CopyToExec) {
         LLVM_DEBUG(dbgs() << "Fold exec copy: " << *PrepareExecInst);
 
         PrepareExecInst->getOperand(0).setReg(Exec);
 
         LLVM_DEBUG(dbgs() << "into: " << *PrepareExecInst << '\n');
 
         CopyToExecInst->eraseFromParent();
+        Changed = true;
       }
 
       continue;
     }
 
     if (isLiveOut(MBB, CopyToExec)) {
       // The copied register is live out and has a second use in another block.
       LLVM_DEBUG(dbgs() << "Exec copy source register is live out\n");
for (MachineBasicBlock &MBB : MF) {
     SaveExecInst->eraseFromParent();
 
     CopyToExecInst->eraseFromParent();
 
     for (MachineInstr *OtherInst : OtherUseInsts) {
       OtherInst->substituteRegister(CopyToExec, Exec,
                                     AMDGPU::NoSubRegister, *TRI);
     }
-  }
 
-  return true;
+    Changed = true;
+  }
 
+  return Changed;
 }