[DAGCombiner] Minor improvements to foldAndOrOfSETCC. NFC

[craig.topper]

Summary

Reduce the scope of some variables.
Replace an if with an assertion.

[kmitropoulou]

LGTM! Thank you!

llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

static SDValue foldAndOrOfSETCC(SDNode *LogicOp, SelectionDAG &DAG) {
   // sequence will be replaced with min-cmp sequence:
   // (LHS0 < LHS1) | (RHS0 < RHS1) -> min(LHS0, RHS0) < LHS1
   // and and-cmp-cmp will be replaced with max-cmp sequence:
   // (LHS0 < LHS1) & (RHS0 < RHS1) -> max(LHS0, RHS0) < LHS1
   if (OpVT.isInteger() && TLI.isOperationLegal(ISD::UMAX, OpVT) &&
       TLI.isOperationLegal(ISD::SMAX, OpVT) &&
       TLI.isOperationLegal(ISD::UMIN, OpVT) &&
       TLI.isOperationLegal(ISD::SMIN, OpVT)) {
-    SDValue CommonValue;
-    SDValue Operand1;
-    SDValue Operand2;
-    ISD::CondCode CC = ISD::SETCC_INVALID;
     if (LHS->getOpcode() == ISD::SETCC && RHS->getOpcode() == ISD::SETCC &&
         LHS->hasOneUse() && RHS->hasOneUse() &&
         // The two comparisons should have either the same predicate or the
         // predicate of one of the comparisons is the opposite of the other one.
         (CCL == CCR || CCL == ISD::getSetCCSwappedOperands(CCR)) &&
         // The optimization does not work for `==` or `!=` .
         !ISD::isIntEqualitySetCC(CCL) && !ISD::isIntEqualitySetCC(CCR)) {
+      SDValue CommonValue, Operand1, Operand2;
+      ISD::CondCode CC = ISD::SETCC_INVALID;
       if (CCL == CCR) {
         if (LHS0 == RHS0) {
           CommonValue = LHS0;
           Operand1 = LHS1;
           Operand2 = RHS1;
           CC = ISD::getSetCCSwappedOperands(CCL);
         } else if (LHS1 == RHS1) {
           CommonValue = LHS1;
           Operand1 = LHS0;
           Operand2 = RHS0;
           CC = CCL;
         }
-      } else if (CCL == ISD::getSetCCSwappedOperands(CCR)) {
+      } else {
+        assert(CCL == ISD::getSetCCSwappedOperands(CCR) && "Unexpected CC");
         if (LHS0 == RHS1) {
           CommonValue = LHS0;
           Operand1 = LHS1;
           Operand2 = RHS0;
           CC = ISD::getSetCCSwappedOperands(CCL);
         } else if (RHS0 == LHS1) {
           CommonValue = LHS1;
           Operand1 = LHS0;