[LoopUnroll][NFC] Remove redundant canPeel check

We check `canPeel` twice: when evaluating the number of iterations to be peeled
and within the method `peelLoop` that performs peeling. This method is only
executed if the calculated peel count is positive. Thus, the check in `peelLoop` can
never fail. This patch replaces this check with an assert.

Differential Revision: https://reviews.llvm.org/D44919
Reviewed By: fhahn

llvm-svn: 328615

llvm/lib/Transforms/Utils/LoopUnrollPeel.cpp

@@ -473,8 +473,8 @@ static void cloneLoopBlocks(Loop *L, unsigned IterNumber, BasicBlock *InsertTop,
 bool llvm::peelLoop(Loop *L, unsigned PeelCount, LoopInfo *LI,
                     ScalarEvolution *SE, DominatorTree *DT,
                     AssumptionCache *AC, bool PreserveLCSSA) {
-  if (!canPeel(L))
-    return false;
+  assert(PeelCount > 0 && "Attempt to peel out zero iterations?");
+  assert(canPeel(L) && "Attempt to peel a loop which is not peelable?");
 
   LoopBlocksDFS LoopBlocks(L);
   LoopBlocks.perform(LI);