[llvm-dev] Problems with registering of ModulePass (with Dependencies)

[John Criswell via llvm-dev]

On 7/10/17 9:57 AM, Gerion Entrup via llvm-dev wrote:
> Hello,
>
> I have created a ModulePass, that now needs LoopInfo information.
> The ModulePass registration is taken from [1]. I use clang to directly invoke
> it (This is also a hard requirement, because I need the fancy output of clang
> warnings/remarks).

It's not clear to me what the problem is, but perhaps your pass 
dependencies are creating circular dependencies that the PassManager 
cannot resolve.  This could happen if LoopInfoWrappersPass, or a pass 
upon which LoopInfoWrappersPass depends, is not a pure analysis pass 
(i.e., it does not preserve the results of all other passes).

To that end, you could try making your pass preserve all other passes 
(using addPreserveAll() in your getAnalysisUsage() method) or check that 
LoopInfoWrappersPass and all passes it uses do not invalidate any passes.

If that doesn't help, then you'll need to dig deeper (using the 
debugger) to figure out why the PassManager is hitting the assertion.  
Using -debug-pass=structure may help.  Tracing back through the control 
flow using the debugger may also provide some insight.

Sorry I can't be more helpful.

Regards,

John Criswell


> The problem is, that the dependency to the LoopInfoWrapperPass does not seem
> to work. The error is:
> --- snip ---
> clang-4.0: /var/tmp/portage/sys-devel/llvm-4.0.1/work/llvm-4.0.1.src/include/llvm/PassAnalysisSupport.h:236:
> AnalysisType& llvm::Pass::getAnalysisID(llvm::AnalysisID) const [with AnalysisType = llvm::LoopInfoWrapperPass; llvm::AnalysisID = const void*]:
> Assertion `ResultPass && "getAnalysis*() called on an analysis that was not " "'required' by pass!"' failed.
> --- /snip ---
>
> The minimal code, that triggers the error is:
> --------- snip ---------
> #include "llvm/Support/raw_ostream.h"
> #include "llvm/ADT/Statistic.h"
> #include "llvm/IR/IRBuilder.h"
> #include "llvm/IR/LegacyPassManager.h"
> #include "llvm/IR/Module.h"
> #include "llvm/Support/Debug.h"
> #include "llvm/Transforms/IPO/PassManagerBuilder.h"
> #include "llvm/Analysis/LoopInfo.h"
>
> using namespace llvm;
>
> namespace {
>          struct SkeletonPass : public ModulePass {
>                  static char ID;
>                  SkeletonPass() : ModulePass(ID) { }
>
>                  virtual bool runOnModule(Module &M) override {
>                          errs() << "In module called: " << M.getName() << "!\n";
>                          LoopInfo& li = getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
>                          return false;
>                  }
>
>                  virtual void getAnalysisUsage(AnalysisUsage& au) const override {
>                          au.setPreservesCFG();
>                          au.addRequired<LoopInfoWrapperPass>();
>                  }
>      };
> }
>
> char SkeletonPass::ID = 0;
>
> //Automatically enable the pass.
> //http://adriansampson.net/blog/clangpass.html
> static void registerSkeletonPass(const PassManagerBuilder &,
>                       legacy::PassManagerBase &PM) {
>          PM.add(new SkeletonPass());
> }
>
> static RegisterStandardPasses
>          RegisterMyPass(PassManagerBuilder::EP_ModuleOptimizerEarly, registerSkeletonPass);
>
> static RegisterStandardPasses
>          RegisterMyPass0(PassManagerBuilder::EP_EnabledOnOptLevel0, registerSkeletonPass);
> -------- /snip------
> Invocation per:
> clang -Xclang -load -Xclang /path/to/llvm-pass-skeleton/build/skeleton/libSkeletonPass.so -g test.c
> I use clang 4.0.1.
>
> Can someone give me an advice, how to fix this and use the LoopInfo?
>
> Gerion
>
> [1]https://github.com/sampsyo/llvm-pass-skeleton/issues/7
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-- 
John Criswell
Assistant Professor
Department of Computer Science, University of Rochester
http://www.cs.rochester.edu/u/criswell

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