New EH representation for MSVC compatibility

This introduces new instructions neccessary to implement MSVC-compatible
exception handling support.  Most of the middle-end and none of the
back-end haven't been audited or updated to take them into account.

Differential Revision: http://reviews.llvm.org/D11097

llvm-svn: 243766

llvm/lib/Transforms/Utils/LoopSimplify.cpp

@@ -142,6 +142,8 @@ BasicBlock *llvm::InsertPreheaderForLoop(Loop *L, Pass *PP) {
   BasicBlock *PreheaderBB;
   PreheaderBB = SplitBlockPredecessors(Header, OutsideBlocks, ".preheader", DT,
                                        LI, PreserveLCSSA);
+  if (!PreheaderBB)
+    return nullptr;
 
   DEBUG(dbgs() << "LoopSimplify: Creating pre-header "
                << PreheaderBB->getName() << "\n");
@@ -178,6 +180,8 @@ static BasicBlock *rewriteLoopExitBlock(Loop *L, BasicBlock *Exit,
 
   NewExitBB = SplitBlockPredecessors(Exit, LoopBlocks, ".loopexit", DT, LI,
                                      PreserveLCSSA);
+  if (!NewExitBB)
+    return nullptr;
 
   DEBUG(dbgs() << "LoopSimplify: Creating dedicated exit block "
                << NewExitBB->getName() << "\n");
@@ -256,8 +260,10 @@ static Loop *separateNestedLoop(Loop *L, BasicBlock *Preheader,
     return nullptr;
 
   // The header is not a landing pad; preheader insertion should ensure this.
-  assert(!L->getHeader()->isLandingPad() &&
-         "Can't insert backedge to landing pad");
+  BasicBlock *Header = L->getHeader();
+  assert(!Header->isLandingPad() && "Can't insert backedge to landing pad");
+  if (!Header->canSplitPredecessors())
+    return nullptr;
 
   PHINode *PN = findPHIToPartitionLoops(L, DT, AC);
   if (!PN) return nullptr;  // No known way to partition.
@@ -285,7 +291,6 @@ static Loop *separateNestedLoop(Loop *L, BasicBlock *Preheader,
 
   bool PreserveLCSSA = PP->mustPreserveAnalysisID(LCSSAID);
 
-  BasicBlock *Header = L->getHeader();
   BasicBlock *NewBB = SplitBlockPredecessors(Header, OuterLoopPreds, ".outer",
                                              DT, LI, PreserveLCSSA);