SCEV: cover a codepath in isImpliedCondBalancedTypes

The code that checks a predicate against a swapped predicate in
isImpliedCondBalancedTypes is not covered by any existing test, within
any Analysis or Transform. Fix this by adding a test to SCEV.

Author: artagnon

llvm/lib/Analysis/ScalarEvolution.cpp

@@ -11872,7 +11872,6 @@ bool ScalarEvolution::isImpliedCondBalancedTypes(
   // FIXME: use CmpPredicate::getMatching here.
   if (ICmpInst::getSwappedCmpPredicate(FoundPred) ==
       static_cast<CmpInst::Predicate>(Pred)) {
-    return false;
     // We can write the implication
     // 0.  LHS Pred      RHS  <-   FoundLHS SwapPred  FoundRHS
     // using one of the following ways:

llvm/test/Analysis/ScalarEvolution/implied-via-division.ll

@@ -416,9 +416,9 @@ define void @swapped_predicate(i32 %n) nounwind {
 ; Prove that (n >= 1) ===> (0 >= -n / 2).
 ; CHECK-LABEL: 'swapped_predicate'
 ; CHECK-NEXT:  Determining loop execution counts for: @swapped_predicate
-; CHECK-NEXT:  Loop %header: backedge-taken count is (-1 * (0 smin (-1 + (-1 * %n.div.2)<nsw>)<nsw>))<nsw>
+; CHECK-NEXT:  Loop %header: backedge-taken count is (1 + %n.div.2)<nsw>
 ; CHECK-NEXT:  Loop %header: constant max backedge-taken count is i32 1073741824
-; CHECK-NEXT:  Loop %header: symbolic max backedge-taken count is (-1 * (0 smin (-1 + (-1 * %n.div.2)<nsw>)<nsw>))<nsw>
+; CHECK-NEXT:  Loop %header: symbolic max backedge-taken count is (1 + %n.div.2)<nsw>
 ; CHECK-NEXT:  Loop %header: Trip multiple is 1
 ;
 entry: