[LCSSA] Add expensive verification of LCSSA form for sub-loops.

This assertion makes sure all sub-loops are in LCSSA form before
bringing their parent in LCSSA form. This precondition was added to
formLCSSA in D56848.

Reviewers: davide, efriedma, mzolotukhin

Reviewed By: davide

Differential Revision: https://reviews.llvm.org/D56921

llvm-svn: 352958

llvm/lib/Transforms/Utils/LCSSA.cpp

@@ -305,6 +305,12 @@ bool llvm::formLCSSA(Loop &L, DominatorTree &DT, LoopInfo *LI,
                      ScalarEvolution *SE) {
   bool Changed = false;
 
+#ifdef EXPENSIVE_CHECKS
+  // Verify all sub-loops are in LCSSA form already.
+  for (Loop *SubLoop: L)
+    assert(SubLoop->isRecursivelyLCSSAForm(DT, *LI) && "Subloop not in LCSSA!");
+#endif
+
   SmallVector<BasicBlock *, 8> ExitBlocks;
   L.getExitBlocks(ExitBlocks);
   if (ExitBlocks.empty())