[NFC][PowerPC] Improve the for loop in Early Return

[ZhangKang]

Summary

In PPCEarlyReturn.cpp

183       for (MachineFunction::iterator I = MF.begin(); I != MF.end();) {
184         MachineBasicBlock &B = *I++;
185         if (processBlock(B))
186           Changed = true;
187       }

Above code can be improved to:

184       for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E;) {
185         MachineBasicBlock &B = *I++;
186         Changed |= processBlock(B);
187       }

[hfinkel]

LGTM

llvm/trunk/lib/Target/PowerPC/PPCEarlyReturn.cpp

bool runOnMachineFunction(MachineFunction &MF) override {
       TII = MF.getSubtarget().getInstrInfo();
 
       bool Changed = false;
 
       // If the function does not have at least two blocks, then there is
       // nothing to do.
       if (MF.size() < 2)
         return Changed;
       
-      for (MachineFunction::iterator I = MF.begin(); I != MF.end();) {
+      // We can't use a range-based for loop due to clobbering the iterator.
+      for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E;) {
         MachineBasicBlock &B = *I++;
-        if (processBlock(B))
-          Changed = true;
+        Changed |= processBlock(B);
       }
 
       return Changed;
     }
 
     MachineFunctionProperties getRequiredProperties() const override {
       return MachineFunctionProperties().set(
           MachineFunctionProperties::Property::NoVRegs);