Add verifyAnalysis for LCSSA.

[mzolotukhin]

Summary

LCSSAWrapperPass currently doesn't override verifyAnalysis method, so pass
manager doesn't verify LCSSA. This patch adds the method so that we start
verifying LCSSA between loop passes.

[sanjoy]

lib/Transforms/Utils/LCSSA.cpp

318 ↗

(On Diff #65818)

I'm missing something here -- how is LCSSA an "analysis" that can be "verified"?

[mzolotukhin]

lib/Transforms/Utils/LCSSA.cpp

318 ↗

(On Diff #65818)

I'm not very confident about this, but my understanding was that if a pass states that it preserves LCSSA (AU.addPreservedID(LCSSAID) like e.g. LoopSimplify does), then pass manager would run verifyAnalysis for LCSSA. In debugger this function is definitely entered several times.

I'd be happy to be corrected here, and add a verifier in some other way.

[sanjoy]

lib/Transforms/Utils/LCSSA.cpp

318 ↗

(On Diff #65818)

Make sense, the Analysis part threw me off.

Does it make sense to use something that would work in release mode also? Or is verifyAnalysis expected to be a no-op in non-debug builds?

[mzolotukhin]

lib/Transforms/Utils/LCSSA.cpp

318 ↗

(On Diff #65818)

is verifyAnalysis expected to be a no-op in non-debug builds?

In LegacyPassManager.cpp it was

void PMDataManager::verifyPreservedAnalysis(Pass *P) {
  // Don't do this unless assertions are enabled.
#ifdef NDEBUG
  return;
#endif
...

So in Release+Assertions and Debug builds it should be on.

[sanjoy]

lgtm

llvm/trunk/lib/Transforms/Utils/LCSSA.cpp

struct LCSSAWrapperPass : public FunctionPass {
   }
 
   // Cached analysis information for the current function.
   DominatorTree *DT;
   LoopInfo *LI;
   ScalarEvolution *SE;
 
   bool runOnFunction(Function &F) override;
+  void verifyAnalysis() const override {
+    assert(
+        all_of(*LI, [&](Loop *L) { return L->isRecursivelyLCSSAForm(*DT); }) &&
+        "LCSSA form is broken!");
+  };
 
   /// This transformation requires natural loop information & requires that
   /// loop preheaders be inserted into the CFG.  It maintains both of these,
   /// as well as the CFG.  It also requires dominator information.
   void getAnalysisUsage(AnalysisUsage &AU) const override {
     AU.setPreservesCFG();
 
     AU.addRequired<DominatorTreeWrapperPass>();