[JumpThreading] Change a dyn_cast that is already protected by an isa check to a static cast. Combine the with another static cast. NFC

[craig.topper]

Summary

I'm looking at possibly making some changes near this code. While doing that I noticed that there was a dyn_cast that was already protected by an earlier isa check. And once we do that we can hoist the cast used in the other if block and only do the cast once.

[efriedma]

lib/Transforms/Scalar/JumpThreading.cpp

583

"Cmp->getType()->isIntegerTy()" is always true, so you could just make this "if (Constant *CmpConst = dyn_cast<Constant>(Cmp->getOperand(1)))".

[craig.topper]

Doesn't isIntegerTy omit vector of integers which would be valid for cmp type?

[efriedma]

Oh, oops, you're right. Could you change it to check isVectorTy() instead, to make that more obvious?

Otherwise LGTM.

lib/Transforms/Scalar/JumpThreading.cpp

if (PN && PN->getParent() == BB) {
           Result.push_back(std::make_pair(KC, PredBB));
       }
 
       return !Result.empty();
     }
 
     // If comparing a live-in value against a constant, see if we know the
     // live-in value on any predecessors.
     if (isa<Constant>(Cmp->getOperand(1)) && Cmp->getType()->isIntegerTy()) {
+      Constant *CmpConst = cast<Constant>(Cmp->getOperand(1));
+
       if (!isa<Instruction>(Cmp->getOperand(0)) ||
           cast<Instruction>(Cmp->getOperand(0))->getParent() != BB) {
-        Constant *RHSCst = cast<Constant>(Cmp->getOperand(1));
-
         for (BasicBlock *P : predecessors(BB)) {
           // If the value is known by LazyValueInfo to be a constant in a
           // predecessor, use that information to try to thread this block.
           LazyValueInfo::Tristate Res =
             LVI->getPredicateOnEdge(Cmp->getPredicate(), Cmp->getOperand(0),
-                                    RHSCst, P, BB, CxtI ? CxtI : Cmp);
+                                    CmpConst, P, BB, CxtI ? CxtI : Cmp);
           if (Res == LazyValueInfo::Unknown)
             continue;
 
           Constant *ResC = ConstantInt::get(Cmp->getType(), Res);
           Result.push_back(std::make_pair(ResC, P));
         }
 
         return !Result.empty();
       }
 
       // Try to find a constant value for the LHS of a comparison,
       // and evaluate it statically if we can.
-      if (Constant *CmpConst = dyn_cast<Constant>(Cmp->getOperand(1))) {
-        PredValueInfoTy LHSVals;
-        ComputeValueKnownInPredecessors(I->getOperand(0), BB, LHSVals,
-                                        WantInteger, CxtI);
 
-        for (const auto &LHSVal : LHSVals) {
-          Constant *V = LHSVal.first;
-          Constant *Folded = ConstantExpr::getCompare(Cmp->getPredicate(),
-                                                      V, CmpConst);
-          if (Constant *KC = getKnownConstant(Folded, WantInteger))
-            Result.push_back(std::make_pair(KC, LHSVal.second));
-        }
 
-        return !Result.empty();
-      }
-    }
-  }
 
   if (SelectInst *SI = dyn_cast<SelectInst>(I)) {
     // Handle select instructions where at least one operand is a known constant
     // and we can figure out the condition value for any predecessor block.
     Constant *TrueVal = getKnownConstant(SI->getTrueValue(), Preference);
     Constant *FalseVal = getKnownConstant(SI->getFalseValue(), Preference);
     PredValueInfoTy Conds;
     if ((TrueVal || FalseVal) &&