[PredicateInfo] return true when the function was modified

[jeroen.dobbelaere]

Summary

The PredicateInfo dumper potentially modifies the function it is analyzing. When that is the case it should report so and return true.

This fixes a bug that shows up with the old pass manager and EXPENSIVE_CHECKS. It was reported In D91661#2875179 by @jroelofs

[jroelofs]

Thank you! LGTM

[fhahn]

This fixes a bug that shows up with the old pass manager and EXPENSIVE_CHECKS. It was reported In D91661#2875179 by @jroelofs

Ok, so the reason is that PredicateInfo does not remove the declarations it created after D91661 and also does not remove the ssa_copy calls? It might be better to restore the behaviour, otherwise we will have to update all passes that use PredicateInfo to mark the function/module as changed, which seems a bit unfortunate.

[jeroen.dobbelaere]

In D105983#2880058, @fhahn wrote:

This fixes a bug that shows up with the old pass manager and EXPENSIVE_CHECKS. It was reported In D91661#2875179 by @jroelofs

Ok, so the reason is that PredicateInfo does not remove the declarations it created after D91661 and also does not remove the ssa_copy calls? It might be better to restore the behaviour, otherwise we will have to update all passes that use PredicateInfo to mark the function/module as changed, which seems a bit unfortunate.

I see. The reverted patch did much more than just fix the name clashes in an ad hoc way. Let me come up with patch that again cleans up what was produced.

llvm/include/llvm/Transforms/Utils/PredicateInfo.h

public:
 
   void dump() const;
   void print(raw_ostream &) const;
 
   const PredicateBase *getPredicateInfoFor(const Value *V) const {
     return PredicateMap.lookup(V);
   }
 
+  // Items added to the PredicateMap correspond to llvm.ssa.copy calls added to
+  // the function.
+  bool modifiedFunction() const { return !PredicateMap.empty(); }
+
 protected:
   // Used by PredicateInfo annotater, dumpers, and wrapper pass.
   friend class PredicateInfoAnnotatedWriter;
   friend class PredicateInfoPrinterLegacyPass;
   friend class PredicateInfoBuilder;
 
 private:
   Function &F;

llvm/lib/Transforms/Utils/PredicateInfo.cpp

 
 bool PredicateInfoPrinterLegacyPass::runOnFunction(Function &F) {
   auto &DT = getAnalysis<DominatorTreeWrapperPass>().getDomTree();
   auto &AC = getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
   auto PredInfo = std::make_unique<PredicateInfo>(F, DT, AC);
   PredInfo->print(dbgs());
   if (VerifyPredicateInfo)
     PredInfo->verifyPredicateInfo();
-  return false;
+  return PredInfo->modifiedFunction();
 }
 
 PreservedAnalyses PredicateInfoPrinterPass::run(Function &F,
                                                 FunctionAnalysisManager &AM) {
   auto &DT = AM.getResult<DominatorTreeAnalysis>(F);
   auto &AC = AM.getResult<AssumptionAnalysis>(F);
   OS << "PredicateInfo for function: " << F.getName() << "\n";
   auto PredInfo = std::make_unique<PredicateInfo>(F, DT, AC);