failed assertion: Cannot split an edge from a CallBrInst

[nickdesaulniers]

testing #1160 w/ assertions enabled, I hit an assertion failure; cvised down:

f;
a(void);
b(void) {
  while (({
    long c;
    if (a()) {
      asm goto("" : : : : d);
      break;
    d:;
    }
    c;
  }))
    return 4;
  return 0;
}
e(int);
do_pages_move_nr_pages(void) {
  int g, a = 0;
  for (;; g++) {
    if (f) a = b();
    if (a) goto h;
  }
h:
  e(g);
}

clang-12: ../lib/Transforms/Utils/BasicBlockUtils.cpp:787: llvm::BasicBlock *llvm::SplitBlockPredecessors(llvm::BasicBlock *, ArrayRef<llvm::BasicBlock *>, const char *, llvm::DominatorTree *, llvm::LoopInfo *, llvm::MemorySSAUpdater *, bool): Assertion `!isa<CallBrInst>(Preds[i]->getTerminator()) && "Cannot split an edge from a CallBrInst"' failed.
PLEASE submit a bug report to https://bugs.llvm.org/ and include the crash backtrace, preprocessed source, and associated run script.
Stack dump:
...
3.      Running pass 'Function Pass Manager' on module 'mm/migrate.c'.
4.      Running pass 'Loop Pass Manager' on function '@do_pages_move'
5.      Running pass 'Loop Strength Reduction' on basic block '%for.body'
 #0 0x00000000040e75e4 PrintStackTraceSignalHandler(void*) (/android0/llvm-project/llvm/build/bin/clang-12+0x40e75e4)
 #1 0x00000000040e51ee llvm::sys::RunSignalHandlers() (/android0/llvm-project/llvm/build/bin/clang-12+0x40e51ee)
 #2 0x00000000040e7905 SignalHandler(int) (/android0/llvm-project/llvm/build/bin/clang-12+0x40e7905)
 #3 0x00007fe120692140 __restore_rt (/lib/x86_64-linux-gnu/libpthread.so.0+0x14140)
 #4 0x00007fe12016adb1 raise ./signal/../sysdeps/unix/sysv/linux/raise.c:51:1
 #5 0x00007fe120154537 abort ./stdlib/abort.c:81:7
 #6 0x00007fe12015440f get_sysdep_segment_value ./intl/loadmsgcat.c:509:8
 #7 0x00007fe12015440f _nl_load_domain ./intl/loadmsgcat.c:970:34
 #8 0x00007fe1201635b2 (/lib/x86_64-linux-gnu/libc.so.6+0x345b2)
 #9 0x00000000040f5ab6 llvm::SplitBlockPredecessors(llvm::BasicBlock*, llvm::ArrayRef<llvm::BasicBlock*>, char const*, llvm::DominatorTree*, llvm::LoopInfo*, llvm::MemorySSAUpdater*, bool) (/android0/llvm-project/llvm/build/bin/clang-12+0x40f5ab6)
#10 0x00000000040fd53f llvm::SplitCriticalEdge(llvm::Instruction*, unsigned int, llvm::CriticalEdgeSplittingOptions const&) (/android0/llvm-project/llvm/build/bin/clang-12+0x40fd53f)
#11 0x0000000003f1c615 (anonymous namespace)::LSRInstance::LSRInstance(llvm::Loop*, llvm::IVUsers&, llvm::ScalarEvolution&, llvm::DominatorTree&, llvm::LoopInfo&, llvm::TargetTransformInfo const&, llvm::AssumptionCache&, llvm::TargetLibraryInfo&, llvm::MemorySSAUpdater*) (/android0/llvm-project/llvm/build/bin/clang-12+0x3f1c615)
#12 0x0000000003f151fe ReduceLoopStrength(llvm::Loop*, llvm::IVUsers&, llvm::ScalarEvolution&, llvm::DominatorTree&, llvm::LoopInfo&, llvm::TargetTransformInfo const&, llvm::AssumptionCache&, llvm::TargetLibraryInfo&, llvm::MemorySSA*) (/android0/llvm-project/llvm/build/bin/clang-12+0x3f151fe)
#13 0x0000000003f3bab6 (anonymous namespace)::LoopStrengthReduce::runOnLoop(llvm::Loop*, llvm::LPPassManager&) (/android0/llvm-project/llvm/build/bin/clang-12+0x3f3bab6)
#14 0x000000000338305b llvm::LPPassManager::runOnFunction(llvm::Function&) (/android0/llvm-project/llvm/build/bin/clang-12+0x338305b)
#15 0x0000000003a32a38 llvm::FPPassManager::runOnFunction(llvm::Function&) (/android0/llvm-project/llvm/build/bin/clang-12+0x3a32a38)
#16 0x0000000003a390f8 llvm::FPPassManager::runOnModule(llvm::Module&) (/android0/llvm-project/llvm/build/bin/clang-12+0x3a390f8)
#17 0x0000000003a330e7 llvm::legacy::PassManagerImpl::run(llvm::Module&) (/android0/llvm-project/llvm/build/bin/clang-12+0x3a330e7)
#18 0x000000000430d482 clang::EmitBackendOutput(clang::DiagnosticsEngine&, clang::HeaderSearchOptions const&, clang::CodeGenOptions const&, clang::TargetOptions const&, clang::LangOptions const&, llvm::DataLayout const&, llvm::Module*, clang::BackendAction, std::unique_ptr<llvm::raw_pwrite_stream, std::default_delete<llvm::raw_pwrite_stream> >) (/android0/llvm-project/llvm/build/bin/clang-12+0x430d482)
#19 0x0000000004b2b9e6 clang::BackendConsumer::HandleTranslationUnit(clang::ASTContext&) (/android0/llvm-project/llvm/build/bin/clang-12+0x4b2b9e6)
#20 0x0000000005b0e4e3 clang::ParseAST(clang::Sema&, bool, bool) (/android0/llvm-project/llvm/build/bin/clang-12+0x5b0e4e3)
#21 0x0000000004a78ce3 clang::FrontendAction::Execute() (/android0/llvm-project/llvm/build/bin/clang-12+0x4a78ce3)
#22 0x00000000049d56e3 clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) (/android0/llvm-project/llvm/build/bin/clang-12+0x49d56e3)
#23 0x0000000004b26022 clang::ExecuteCompilerInvocation(clang::CompilerInstance*) (/android0/llvm-project/llvm/build/bin/clang-12+0x4b26022)
#24 0x000000000287eecd cc1_main(llvm::ArrayRef<char const*>, char const*, void*) (/android0/llvm-project/llvm/build/bin/clang-12+0x287eecd)
#25 0x000000000287cf7c ExecuteCC1Tool(llvm::SmallVectorImpl<char const*>&) (/android0/llvm-project/llvm/build/bin/clang-12+0x287cf7c)
#26 0x000000000287cce1 main (/android0/llvm-project/llvm/build/bin/clang-12+0x287cce1)
#27 0x00007fe120155cca __libc_start_main ./csu/../csu/libc-start.c:308:16
#28 0x0000000002879c3a _start (/android0/llvm-project/llvm/build/bin/clang-12+0x2879c3a)

cc @gwelymernans @jyknight

[nickdesaulniers]

ah, need to add the command line flags to repro, let me pare those down.

[nickdesaulniers]

$ clang -O2 migrate.i -ftrivial-auto-var-init=pattern --target=powerpc64le-linux-gnu

Might be able to drop -ftrivial-auto-var-init=pattern by initializing some things.

[nickdesaulniers]

Yes, initializing c to 1 and g to -4 allows me to drop -ftrivial-auto-var-init=pattern. I still need --target=powerpc64le-linux-gnu though.

[bwendling]

Could you post the IR?

[nickdesaulniers]

Somehow, if I dump the IR, I can't reproduce by invoking llc on it...

[bwendling]

Try invoking opt -O2

[nickdesaulniers]

diff --git a/llvm/lib/Transforms/Utils/BreakCriticalEdges.cpp b/llvm/lib/Transforms/Utils/BreakCriticalEdges.cpp
index 39fb504cf7b7..e88bdc8bf476 100644
--- a/llvm/lib/Transforms/Utils/BreakCriticalEdges.cpp
+++ b/llvm/lib/Transforms/Utils/BreakCriticalEdges.cpp
@@ -186,7 +186,8 @@ llvm::SplitCriticalEdge(Instruction *TI, unsigned SuccNum,
       // Loop-simplify form can be preserved, if we can split all in-loop
       // predecessors.
       if (any_of(LoopPreds, [](BasicBlock *Pred) {
-            return isa<IndirectBrInst>(Pred->getTerminator());
+            return isa<IndirectBrInst>(Pred->getTerminator()) ||
+              isa<CallBrInst>(Pred->getTerminator());
           })) {
         if (Options.PreserveLoopSimplify)
           return nullptr;

seems to fix this. Not sure yet about getting a work reproducer in IR, or what the consequences of that change precisely are.

[nickdesaulniers]

this issue is reminiscent of #896

[nickdesaulniers]

Somehow, if I dump the IR, I can't reproduce by invoking llc on it...

Note to future self; use clang -mllvm -print-after-all -mllvm -print-module-scope, but use a dump of post-verification pass, not a post loop transform!

attaching minimal reproducer:

$ clang -O2 --target=powerpc64le reduced.ll

reduced.ll.txt

I haven't been able to figure out how to get it to crash by just invoking llc...

[bwendling]

llc generates asm code. opt performs the IR transformations. I think you want to use opt and not llc.

[nickdesaulniers]

https://reviews.llvm.org/D88438

[nathanchance]

Ha, I thought I remember that #1252 looked familiar... I assume Bill's patch will fix this one too?

[nickdesaulniers]

oh, yeah, looks similar, cc @gwelymernans @MaskRay