The crash backtrace goes like this:

#​0 0x00000008060c93fa in thr_kill () from /lib/libc.so.7
#​1 0x00000008060c9368 in raise () from /lib/libc.so.7
#​2 0x00000008060c78e9 in abort () from /lib/libc.so.7
#​3 0x00000008060a6a61 in assert () from /lib/libc.so.7
#​4 0x000000000161500b in llvm::SplitCriticalEdge (TI=0x806d590e0, SuccNum=1, Options=...) at /share/dim/src/llvm/git/lib/Transforms/Utils/BreakCriticalEdges.cpp:138
#​5 0x0000000001459e1c in llvm::SplitCriticalEdge (Src=0x806c179c0, Dst=0x806c174c0, Options=...) at /share/dim/src/llvm/git/include/llvm/Transforms/Utils/BasicBlockUtils.h:181
#​6 0x000000000149df4d in (anonymous namespace)::LoopRotate::rotateLoop (this=0x806c16a40, L=0x806c2c4c0, SimplifiedLatch=false) at /share/dim/src/llvm/git/lib/Transforms/Scalar/LoopRotation.cpp:541
#​7 0x000000000149cc42 in (anonymous namespace)::LoopRotate::runOnLoop (this=0x806c16a40, L=0x806c2c4c0, LPM=...) at /share/dim/src/llvm/git/lib/Transforms/Scalar/LoopRotation.cpp:118
#​8 0x00000000023436d2 in llvm::LPPassManager::runOnFunction (this=0x806ccc000, F=...) at /share/dim/src/llvm/git/lib/Analysis/LoopPass.cpp:250
#​9 0x0000000001109620 in llvm::FPPassManager::runOnFunction (this=0x806d29500, F=...) at /share/dim/src/llvm/git/lib/IR/LegacyPassManager.cpp:1530
#​10 0x0000000002306212 in (anonymous namespace)::CGPassManager::RunPassOnSCC (this=0x806d29340, P=0x806d29500, CurSCC=..., CG=..., CallGraphUpToDate=@0x7fffffffa40e: true, DevirtualizedCall=@0x7fffffffa54b: false) at /share/dim/src/llvm/git/lib/Analysis/IPA/CallGraphSCCPass.cpp:151
#​11 0x0000000002305af0 in (anonymous namespace)::CGPassManager::RunAllPassesOnSCC (this=0x806d29340, CurSCC=..., CG=..., DevirtualizedCall=@0x7fffffffa54b: false) at /share/dim/src/llvm/git/lib/Analysis/IPA/CallGraphSCCPass.cpp:416
#​12 0x000000000230520c in (anonymous namespace)::CGPassManager::runOnModule (this=0x806d29340, M=...) at /share/dim/src/llvm/git/lib/Analysis/IPA/CallGraphSCCPass.cpp:472
#​13 0x000000000110a296 in (anonymous namespace)::MPPassManager::runOnModule (this=0x806ccbc00, M=...) at /share/dim/src/llvm/git/lib/IR/LegacyPassManager.cpp:1608
#​14 0x0000000001109bde in llvm::legacy::PassManagerImpl::run (this=0x806c82c00, M=...) at /share/dim/src/llvm/git/lib/IR/LegacyPassManager.cpp:1715
#​15 0x000000000110aa81 in llvm::legacy::PassManager::run (this=0x806c18240, M=...) at /share/dim/src/llvm/git/lib/IR/LegacyPassManager.cpp:1748
#​16 0x0000000001dd22d3 in (anonymous namespace)::EmitAssemblyHelper::EmitAssembly (this=0x7fffffffad30, Action=clang::Backend_EmitAssembly, OS=0x806c16300) at /share/dim/src/llvm/git/tools/clang/lib/CodeGen/BackendUtil.cpp:629
#​17 0x0000000001dd1a52 in clang::EmitBackendOutput (Diags=..., CGOpts=..., TOpts=..., LOpts=..., TDesc=..., M=0x806c7cc00, Action=clang::Backend_EmitAssembly, OS=0x806c16300) at /share/dim/src/llvm/git/tools/clang/lib/CodeGen/BackendUtil.cpp:646
#​18 0x0000000001db419f in clang::BackendConsumer::HandleTranslationUnit (this=0x806c3a180, C=...) at /share/dim/src/llvm/git/tools/clang/lib/CodeGen/CodeGenAction.cpp:174
#​19 0x0000000002bceda0 in clang::ParseAST (S=..., PrintStats=false, SkipFunctionBodies=false) at /share/dim/src/llvm/git/tools/clang/lib/Parse/ParseAST.cpp:151
#​20 0x00000000018f728a in clang::ASTFrontendAction::ExecuteAction (this=0x806c4a0f0) at /share/dim/src/llvm/git/tools/clang/lib/Frontend/FrontendAction.cpp:526
#​21 0x0000000001db2bde in clang::CodeGenAction::ExecuteAction (this=0x806c4a0f0) at /share/dim/src/llvm/git/tools/clang/lib/CodeGen/CodeGenAction.cpp:727
#​22 0x00000000018f6440 in clang::FrontendAction::Execute (this=0x806c4a0f0) at /share/dim/src/llvm/git/tools/clang/lib/Frontend/FrontendAction.cpp:428
#​23 0x000000000189950e in clang::CompilerInstance::ExecuteAction (this=0x806c31140, Act=...) at /share/dim/src/llvm/git/tools/clang/lib/Frontend/CompilerInstance.cpp:811
#​24 0x0000000001a76577 in clang::ExecuteCompilerInvocation (Clang=0x806c31140) at /share/dim/src/llvm/git/tools/clang/lib/FrontendTool/ExecuteCompilerInvocation.cpp:222
#​25 0x00000000007629f1 in cc1_main (Argv=..., Argv0=0x7fffffffe808 "/home/dim/obj/llvm-fkp-test/bin/clang", MainAddr=0x754d60 <GetExecutablePath(char const*, bool)>) at /share/dim/src/llvm/git/tools/clang/tools/driver/cc1_main.cpp:110
#​26 0x0000000000756b1b in ExecuteCC1Tool (argv=..., Tool=...) at /share/dim/src/llvm/git/tools/clang/tools/driver/driver.cpp:369
#​27 0x00000000007552d2 in main (argc=7, argv=0x7fffffffe548) at /share/dim/src/llvm/git/tools/clang/tools/driver/driver.cpp:415

It's invalid to split a critical edge (i.e. an edge from a block wiht multiple successors to a block with multiple predecessors), that starts at IndirectrBrinst.
I think the right behaviour is that of stopping the rotation of the loop, e.g.

Index: LoopRotation.cpp

--- LoopRotation.cpp (revision 229962)
+++ LoopRotation.cpp (working copy)
@@ -535,6 +535,8 @@
Loop *PredLoop = LI->getLoopFor(*PI);
if (!PredLoop || PredLoop->contains(Exit))
continue;

•  if (!isa<IndirectBrInst>(*TI))
  

•    return false;
   SplitLatchEdge |= L->getLoopLatch() == *PI;
   BasicBlock *ExitSplit = SplitCriticalEdge(
       *PI, Exit, CriticalEdgeSplittingOptions(DT, LI).setPreserveLCSSA());
  

I'm not sure this is 100% correct because I didn't analyze all the side-effects, but it's a start (among others, it passes clang test suite without complaining). Can you give it a shot and see the compiled executable is valid? I'll investigate further on this and ask for review once I'll be more confident

r230058 should help.