[LLVMdev] 2.9 segfault when requesting for both LoopInfo and DominatorTree analyses.

[Duncan Sands]

Hi Michael,

> When migrating my project to 2.9, I've encountered a strange segfault
> where if a ModulePass's getAnalysisUsage adds LoopInfo and
> DominatorTree, then llvm::PMTopLevelManager::findAnalysisUsage will
> segfault.

I suggest you build LLVM with assertions enabled - then you should get a
helpful error message rather than a segfault.  I think you are not allowed
to use LoopInfo from a ModulePass, but I don't recall the details.  This
came up several times already on the mailing list, so I suggest you search
the archives.

Ciao, Duncan.

  What's odd is that if I rearrange this (add required for
> DominatorTree before LoopInfo), it does not segfault. I realize that
> LoopInfo requires and preserves DominatorTree, but this behavior is
> strange. All my other passes migrated fine (after adding in code to do
> the initializations), but perhaps I'm still not initializing
> everything properly?. Below is an example program and it's stack trace
> and debug info.
>
> #include "llvm/Pass.h"
> #include "llvm/PassManager.h"
> #include "llvm/Analysis/Dominators.h"
> #include "llvm/Analysis/LoopInfo.h"
>
> using namespace llvm;
>
> // Forward decl
> namespace llvm {
>      void initializeFooPass(PassRegistry&);
> } // end namespace llvm
>
> namespace  {
>      class Foo : public ModulePass {
>      public:
>          Foo() : ModulePass(ID) {
>              initializeFooPass(*PassRegistry::getPassRegistry());
>          }
>
>          ~Foo() { }
>
>          static char ID;
>          bool runOnModule(Module&);
>          void print(std::ostream&, const Module*) const;
>          void getAnalysisUsage(AnalysisUsage&) const;
>      };
> } // end namespace
>
> bool Foo::runOnModule(Module&M) {
>      return false;
> }
>
> void Foo::getAnalysisUsage(AnalysisUsage&AU) const {
>      AU.addRequired<LoopInfo>();
>      AU.addRequired<DominatorTree>();
> }
>
> void Foo::print(std::ostream&, const Module*) const { }
>
> char Foo::ID = 0;
> INITIALIZE_PASS_BEGIN(Foo, "foo", "foo bar", true, true)
> INITIALIZE_PASS_DEPENDENCY(LoopInfo)
> INITIALIZE_PASS_DEPENDENCY(DominatorTree)
> INITIALIZE_PASS_END(Foo, "foo", "foo bar", true, true)
>
> Foo *createFooPass() {
>      return new Foo();
> }
>
> void runFooPass(Module&M)
> {
>      PassManager PM;
>      PM.add(createFooPass());
>      PM.run(M);
> }
>
>
> Program received signal SIGSEGV, Segmentation fault.
>
> #0  0x0832312f in llvm::PMTopLevelManager::findAnalysisUsage
> (this=0x86f798c, P=0x892bfc0) at
> <...>/llvm-2.9/lib/VMCore/PassManager.cpp:577
> #1  0x08322cfb in llvm::PMTopLevelManager::setLastUser
> (this=0x86f798c, AnalysisPasses=..., P=0x892d2e0) at
> <...>/llvm-2.9/lib/VMCore/PassManager.cpp:516
> #2  0x083275f5 in llvm::MPPassManager::addLowerLevelRequiredPass
> (this=0x885cc60, P=0x892d2e0, RequiredPass=0x892bfc0) at
> <...>/llvm-2.9/lib/VMCore/PassManager.cpp:1608
> #3  0x08324cef in llvm::PMDataManager::add (this=0x885cc70,
> P=0x892d2e0, ProcessAnalysis=true) at
> <...>/llvm-2.9/lib/VMCore/PassManager.cpp:989
> #4  0x08327f11 in llvm::ModulePass::assignPassManager (this=0x892d2e0,
> PMS=..., PreferredType=llvm::PMT_ModulePassManager) at
> <...>/llvm-2.9/lib/VMCore/PassManager.cpp:1768
> #5  0x08329b11 in llvm::PassManagerImpl::addTopLevelPass
> (this=0x885cab8, P=0x892d2e0) at
> <...>/llvm-2.9/lib/VMCore/PassManager.cpp:423
> #6  0x0832339f in llvm::PMTopLevelManager::schedulePass
> (this=0x885cb8c, P=0x892d2e0) at
> <...>/llvm-2.9/lib/VMCore/PassManager.cpp:639
> #7  0x083299dc in llvm::PassManagerImpl::add (this=0x885cab8,
> P=0x892d2e0) at<...>/llvm-2.9/lib/VMCore/PassManager.cpp:396
> #8  0x083279e5 in llvm::PassManager::addImpl (this=0xbffe9578,
> P=0x892d2e0) at<...>/llvm-2.9/lib/VMCore/PassManager.cpp:1659
> #9  0x08327b0a in llvm::PassManager::add (this=0xbffe9578,
> P=0x892d2e0) at<...>/llvm-2.9/lib/VMCore/PassManager.cpp:1672
> #10 0x08089480 in runFooPass (M=...) at<...>/Hello.h:56
> ...
>
> At that point, the variable "P" is
>
> $9 = {_vptr.Pass = 0x0, Resolver = 0x0, PassID = 0x8533e00, Kind =
> llvm::PT_Function}
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