[mips] Always run the MipsOptimizePICCall pass.

[vkalintiris]

Summary

Remove this pass from addMachineSSAOptimization() and register it unconditionally in through addPreRegAlloc(). This pass is required for generating correct PIC calls.

[sdardis]

LGTM.

lib/Target/Mips/MipsTargetMachine.cpp

public:
   }
 
   const MipsSubtarget &getMipsSubtarget() const {
     return *getMipsTargetMachine().getSubtargetImpl();
   }
 
   void addIRPasses() override;
   bool addInstSelector() override;
-  void addMachineSSAOptimization() override;
   void addPreEmitPass() override;
 
   void addPreRegAlloc() override;
 
 };
 } // namespace
 
 TargetPassConfig *MipsTargetMachine::createPassConfig(PassManagerBase &PM) {

 // the ISelDag to gen Mips code.
 bool MipsPassConfig::addInstSelector() {
   addPass(createMipsModuleISelDagPass(getMipsTargetMachine()));
   addPass(createMips16ISelDag(getMipsTargetMachine(), getOptLevel()));
   addPass(createMipsSEISelDag(getMipsTargetMachine(), getOptLevel()));
   return false;
 }
 
-void MipsPassConfig::addMachineSSAOptimization() {
-  addPass(createMipsOptimizePICCallPass(getMipsTargetMachine()));
-  TargetPassConfig::addMachineSSAOptimization();
-}
-
 void MipsPassConfig::addPreRegAlloc() {
-  if (getOptLevel() == CodeGenOpt::None)
-    addPass(createMipsOptimizePICCallPass(getMipsTargetMachine()));
 }
 
 TargetIRAnalysis MipsTargetMachine::getTargetIRAnalysis() {
   return TargetIRAnalysis([this](const Function &F) {
     if (Subtarget->allowMixed16_32()) {
       DEBUG(errs() << "No Target Transform Info Pass Added\n");
       // FIXME: This is no longer necessary as the TTI returned is per-function.
       return TargetTransformInfo(F.getParent()->getDataLayout());