[LoopSimplify] Add opt-bisect support to LoopSimplify pass

[craig.topper]

Summary

This patch adds the skipFunction call so that LoopSimplify will partcipate.

[andrew.w.kaylor]

It looks like a number of passes have this as a required analysis pass, and some assert that loops are in the simplified form. Can you verify that all passes which depend on this pass can also be skipped by opt-bisect?

[andrew.w.kaylor]

Oops. I didn't mean to accept the revision yet.

[chandlerc]

What Andrew said.

The legacy pass manager does actually use this in pass-form by using implicit "requires" from the analysis stuff. And they'll crash if it isn't in simplified form.

We could add opt-bisect support to the pass, but it would need to be controlled very differently for cases where it isn't a fundamental requirement.

lib/Transforms/Utils/LoopSimplify.cpp

 // Publicly exposed interface to pass...
 char &llvm::LoopSimplifyID = LoopSimplify::ID;
 Pass *llvm::createLoopSimplifyPass() { return new LoopSimplify(); }
 
 /// runOnFunction - Run down all loops in the CFG (recursively, but we could do
 /// it in any convenient order) inserting preheaders...
 ///
 bool LoopSimplify::runOnFunction(Function &F) {
+  if (skipFunction(F))
+    return false;
+
   bool Changed = false;
   LoopInfo *LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
   DominatorTree *DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
   auto *SEWP = getAnalysisIfAvailable<ScalarEvolutionWrapperPass>();
   ScalarEvolution *SE = SEWP ? &SEWP->getSE() : nullptr;
   AssumptionCache *AC =
       &getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);