[ValueTracking] Replace an always false condition with an assert.

[craig.topper]

Summary

The one caller of this function already checked that V isn't a
Constant.

Alternatively, we could remove the check from the caller if reviewers
prefer.

[spatel]

llvm/lib/Analysis/ValueTracking.cpp

2302

Change the function signature to take "Constant *C" instead of a generic "Value *"?

[craig.topper]

llvm/lib/Analysis/ValueTracking.cpp

2302

We want to exclude constants.

[spatel]

LGTM

llvm/lib/Analysis/ValueTracking.cpp

2302

Oops. :)

llvm/lib/Analysis/ValueTracking.cpp

for (gep_type_iterator GTI = gep_type_begin(GEP), GTE = gep_type_end(GEP);
 
     if (isKnownNonZero(GTI.getOperand(), Depth, Q))
       return true;
   }
 
   return false;
 }
 
 static bool isKnownNonNullFromDominatingCondition(const Value *V,
                                                   const Instruction *CtxI,
                                                   const DominatorTree *DT) {
-  if (isa<Constant>(V))
-    return false;
+  assert(!isa<Constant>(V) && "Called for constant?");
 
   if (!CtxI || !DT)
     return false;
 
   unsigned NumUsesExplored = 0;
   for (const auto *U : V->users()) {
     // Avoid massive lists
     if (NumUsesExplored >= DomConditionsMaxUses)