[llvm-dev] How can I use llvm::LoopInfo in the runOnModule method?

[J Skye via llvm-dev]

Hi all,

I tried to have a LoopInfo object in a function pass, and add addRequired in getAnalysisUsage, and then use getAnalysis in runOnFunction(). It worked OK.
Now I want to have a module pass to traverse the functions, and similarly, I want to have to loop information of the functions.
When I did the above in runOnModule, and build the module pass, the following error popped out, and the compile did not succeed:

[ 50%] Building CXX object src/CMakeFiles/SkeletonPass.dir/Skeleton.cpp.o
/home/**/Desktop/skeleton/src/Skeleton.cpp: In member function ‘virtual bool llvm::SkeletonPass::runOnModule(llvm::Module&)’:
/home/**/Desktop/skeleton/src/Skeleton.cpp:47:43: error: no matching function for call to ‘llvm::SkeletonPass::getAnalysis(llvm::Function*&)’
     LoopInfo &LI = getAnalysis<LoopInfo>(F);

...
home/**/Work/llvm-6.0.1.src/include/llvm/PassAnalysisSupport.h: In instantiation of ‘llvm::AnalysisUsage& llvm::AnalysisUsage::addRequired() [with PassClass = llvm::LoopInfo]’:
/home/**/Desktop/skeleton/src/Skeleton.cpp:24:38:   required from here
/home/**/Work/llvm-6.0.1.src/include/llvm/PassAnalysisSupport.h:67:39: error: ‘ID’ is not a member of ‘llvm::LoopInfo’
     return addRequiredID(PassClass::ID);
                                       ^

Here is my source code:

#include "llvm/Pass.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/Module.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/IR/Dominators.h"
#include "llvm/Analysis/LoopInfo.h"

namespace llvm
{
    class SkeletonPass : public ModulePass
    {
    public:
        static char ID;
        SkeletonPass() : ModulePass(ID) {}
        bool runOnModule(Module &M) override;
        virtual StringRef getPassName() const override
        {
            return "Skeleton";
        }
        virtual void getAnalysisUsage(AnalysisUsage &AU) const override {
            errs() << "get analysis usage method.\n";
            AU.addRequired<LoopInfo>();
        }
    };

    Pass *createSkeletonPass()
    {
        return new SkeletonPass();
    }

    char SkeletonPass::ID = 0;
    Pass *createSkeletonPass();
    void initializeSkeletonPass(PassRegistry &Registry);


} // namespace llvm

using namespace llvm;
using namespace std;


bool SkeletonPass::runOnModule(llvm::Module &M){
    errs() << "=============start=============\n";
    auto F = M.getFunction("main");
    LoopInfo &LI = getAnalysis<LoopInfo>(F);

    LI.print(errs());
    errs() << "==========================\n";
}

static RegisterPass<SkeletonPass> X("run", "Hello world pass", false, false);

The version of LLVM is 6.0.1, can anyone tell me the correct way to handle this in a module pass? Thanks a lot!

Best,
Liu

[Jonathan Smith via llvm-dev]

It should be `LoopInfoWrapperPass` instead of just `LoopInfo`, but you
can also get the same information if you manually construct a
dominator tree and target info first and pass those to the LoopInfo
constructor.

> _______________________________________________
> LLVM Developers mailing list
> llvm...@lists.llvm.org
> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
_______________________________________________
LLVM Developers mailing list
llvm...@lists.llvm.org
https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev

[David Greene via llvm-dev]

Interesting that we're getting a relative flood of these recently.

See here:

http://lists.llvm.org/pipermail/llvm-dev/2019-March/131346.html

I don't think one can reliably get a Function analysis pass from within
a ModulePass using the legacy pass manager. You have to manually
construct the pass yourself.

-David

[Jonathan Smith via llvm-dev]

I saw this (or perhaps an earlier, similar message) before and that
was enough for me to avoid trying it.

The good thing is it's easy enough to get a LoopInfo manually without
constructing a pass at all:

llvm::DominatorTree domTree{&func, func};
llvm::LoopInfo loopInfo{&func, domTree};

[Florian Hahn via llvm-dev]

On Apr 3, 2019, at 17:40, David Greene via llvm-dev <llvm...@lists.llvm.org> wrote:

I don't think one can reliably get a Function analysis pass from within
a ModulePass using the legacy pass manager.  You have to manually
construct the pass yourself.

That’s strange. AFAIK IPSCCP does exactly that for the DT analysis, see getAnalysis in 

   https://github.com/llvm/llvm-project/blob/master/llvm/lib/Transforms/IPO/SCCP.cpp#L53

Which is called for each function in the module:

  https://github.com/llvm/llvm-project/blob/master/llvm/lib/Transforms/Scalar/SCCP.cpp#L1960

It does not seem like the legacy pass manager is able to preserve Function analyses from Module passes, whereas the new pass manager can, however.

Cheers,

Florian

[David Greene via llvm-dev]

Florian Hahn <floria...@apple.com> writes:

> On Apr 3, 2019, at 17:40, David Greene via llvm-dev <llvm...@lists.llvm.org> wrote:
>
> I don't think one can reliably get a Function analysis pass from within
> a ModulePass using the legacy pass manager. You have to manually
> construct the pass yourself.
>
> That’s strange. AFAIK IPSCCP does exactly that for the DT analysis, see getAnalysis in
> https://github.com/llvm/llvm-project/blob/master/llvm/lib/Transforms/IPO/SCCP.cpp#L53

Yes, I know. That's what I modeled my solution after. And it worked
for a bunch of codes I ran it on. Until it didn't.

I think IPSCCP is broken because the on-the-fly pass manager stuff is
broken.

> It does not seem like the legacy pass manager is able to preserve
> Function analyses from Module passes, whereas the new pass manager
> can, however.

It's not about preserving analyses. The analyses are not safely
available within the ModulePass itself. They get deleted sometime
during the sequence of calls to getAnalysis.

-David