Make sure function passes are run

[JesperAntonsson]

Summary

This is a correction to bug 27509.

The reason for the fix is that optlevel flags might have been be cleared, apparently in order to not rerun the AddOptimizationPasses() function. However, this makes us not run FPasses, which should be wrong.

[patrik.h.hagglund]

Using FPasses exactly when it is initialized (using the replaced condition at line 499) looks like the right thing to do. LGTM.

[JesperAntonsson]

rL272770

tools/opt/opt.cpp

if (OptLevelOs)
     AddOptimizationPasses(Passes, *FPasses, TM.get(), 2, 1);
 
   if (OptLevelOz)
     AddOptimizationPasses(Passes, *FPasses, TM.get(), 2, 2);
 
   if (OptLevelO3)
     AddOptimizationPasses(Passes, *FPasses, TM.get(), 3, 0);
 
-  if (OptLevelO1 || OptLevelO2 || OptLevelOs || OptLevelOz || OptLevelO3) {
+  if (FPasses) {
     FPasses->doInitialization();
     for (Function &F : *M)
       FPasses->run(F);
     FPasses->doFinalization();
   }
 
   // Check that the module is well formed on completion of optimization
   if (!NoVerify && !VerifyEach)