[LPM] Factor all of the loop analysis usage updates into a common helper routine.

[chandlerc]

Summary

We were getting this wrong in small ways and generally being very
inconsistent about it across loop passes. Instead, let's have a common
place where we do this. One minor downside is that this will require
some analyses like SCEV in more places than they are strictly needed.
However, this seems benign as these analyses are complete no-ops, and
without this consistency we can in many cases end up with the legacy
pass manager scheduling deciding to split up a loop pass pipeline in
order to run the function analysis half-way through. It is very, very
annoying to fix these without just being very pedantic across the board.

The only loop passes I've not updated here are ones that use
AU.setPreservesAll() such as IVUsers (an analysis) and the pass printer.
They seemed less relevant.

With this patch, almost all of the problems in PR24804 around loop pass
pipelines are fixed. The one remaining issue is that we run simplify-cfg
and instcombine in the middle of the loop pass pipeline. We've recently
added some loop variants of these passes that would seem substantially
cleaner to use, but this at least gets us much closer to the previous
state. Notably, the seven loop pass managers is down to three.

Note that this doesn't currently pass tests because in changing this, I've made
the INITIALIZE_PASS_DEPENDENCY nonsense totally not work. I'll fix that, but
that won't change the substantive parts of this patch that I'd really like to
get review feedback on -- essentially, is this a reasonable approach?

[jmolloy]

This LGTM.

[chandlerc]

Update the patch with tests, and to remove changes to passes that doen't
actually need them. This now passes all tests while reducing the pass pipelines
as desired.

[jmolloy]

Small comment typos.

also, should we add this to WritingAnLLVMPass.rst?

lib/Transforms/Utils/LoopUtils.cpp

771

generic. dependency.

[chandlerc]

Thanks, landing based on confirmed LGTM on IRC.

In D17435#356845, @jmolloy wrote:

Small comment typos.

Fixed.

also, should we add this to WritingAnLLVMPass.rst?

Follow-up patch will be forthcoming.

include/llvm/InitializePasses.h

 void initializeLintPass(PassRegistry&);
 void initializeLiveDebugVariablesPass(PassRegistry&);
 void initializeLiveIntervalsPass(PassRegistry&);
 void initializeLiveRegMatrixPass(PassRegistry&);
 void initializeLiveStacksPass(PassRegistry&);
 void initializeLiveVariablesPass(PassRegistry&);
 void initializeLoaderPassPass(PassRegistry&);
 void initializeLocalStackSlotPassPass(PassRegistry&);
+void initializeLoopPassPass(PassRegistry&);
 void initializeLoopDeletionPass(PassRegistry&);
 void initializeLoopExtractorPass(PassRegistry&);
 void initializeLoopInfoWrapperPassPass(PassRegistry&);
 void initializeLoopInterchangePass(PassRegistry &);
 void initializeLoopInstSimplifyPass(PassRegistry&);
 void initializeLoopRotatePass(PassRegistry&);
 void initializeLoopSimplifyPass(PassRegistry&);
 void initializeLoopSimplifyCFGPass(PassRegistry&);

include/llvm/Transforms/Utils/LoopUtils.h

 
 /// \brief Check string metadata into loop, if it exist return true,
 /// else return false.
 bool checkStringMetadataIntoLoop(Loop *TheLoop, StringRef Name);
 
 /// \brief Set input string into loop metadata by keeping other values intact.
 void addStringMetadataToLoop(Loop *TheLoop, const char *MDString, 
                              unsigned V = 0);
+
+/// Helper to consistently add the set of standard passes to a loop pass's \c
+/// AnalysisUsage.
+///
+/// All loop passes should call this as part of implementing their \c
+/// getAnalysisUsage.
+void getLoopAnalysisUsage(AnalysisUsage &AU);
+
 }
 
 #endif

lib/Transforms/Scalar/IndVarSimplify.cpp

public:
   IndVarSimplify()
     : LoopPass(ID), LI(nullptr), SE(nullptr), DT(nullptr), Changed(false) {
     initializeIndVarSimplifyPass(*PassRegistry::getPassRegistry());
   }
 
   bool runOnLoop(Loop *L, LPPassManager &LPM) override;
 
   void getAnalysisUsage(AnalysisUsage &AU) const override {
-    AU.addRequired<DominatorTreeWrapperPass>();
-    AU.addRequired<LoopInfoWrapperPass>();
-    AU.addRequired<ScalarEvolutionWrapperPass>();
-    AU.addRequiredID(LoopSimplifyID);
-    AU.addRequiredID(LCSSAID);
-    AU.addPreserved<GlobalsAAWrapperPass>();
-    AU.addPreserved<ScalarEvolutionWrapperPass>();
-    AU.addPreservedID(LoopSimplifyID);
-    AU.addPreservedID(LCSSAID);
     AU.setPreservesCFG();
+    getLoopAnalysisUsage(AU);
   }
 
 private:
   void releaseMemory() override {
     DeadInsts.clear();
   }
 
   bool isValidRewrite(Value *FromVal, Value *ToVal);
private:
   Value *expandSCEVIfNeeded(SCEVExpander &Rewriter, const SCEV *S, Loop *L,
                             Instruction *InsertPt, Type *Ty);
 };
 }
 
 char IndVarSimplify::ID = 0;
 INITIALIZE_PASS_BEGIN(IndVarSimplify, "indvars",
                 "Induction Variable Simplification", false, false)
-INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
-INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)
-INITIALIZE_PASS_DEPENDENCY(ScalarEvolutionWrapperPass)
-INITIALIZE_PASS_DEPENDENCY(LoopSimplify)
-INITIALIZE_PASS_DEPENDENCY(LCSSA)
+INITIALIZE_PASS_DEPENDENCY(LoopPass)
 INITIALIZE_PASS_END(IndVarSimplify, "indvars",
                 "Induction Variable Simplification", false, false)
 
 Pass *llvm::createIndVarSimplifyPass() {
   return new IndVarSimplify();
 }
 
 /// Return true if the SCEV expansion generated by the rewriter can replace the

lib/Transforms/Scalar/InductiveRangeCheckElimination.cpp

 public:
   static char ID;
   InductiveRangeCheckElimination() : LoopPass(ID) {
     initializeInductiveRangeCheckEliminationPass(
         *PassRegistry::getPassRegistry());
   }
 
   void getAnalysisUsage(AnalysisUsage &AU) const override {
-    AU.addRequired<LoopInfoWrapperPass>();
-    AU.addRequiredID(LoopSimplifyID);
-    AU.addRequiredID(LCSSAID);
-    AU.addRequired<ScalarEvolutionWrapperPass>();
     AU.addRequired<BranchProbabilityInfoWrapperPass>();
+    getLoopAnalysisUsage(AU);
   }
 
   bool runOnLoop(Loop *L, LPPassManager &LPM) override;
 };
 
 char InductiveRangeCheckElimination::ID = 0;
 }
 
 INITIALIZE_PASS_BEGIN(InductiveRangeCheckElimination, "irce",
                       "Inductive range check elimination", false, false)
-INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)
-INITIALIZE_PASS_DEPENDENCY(LoopSimplify)
-INITIALIZE_PASS_DEPENDENCY(LCSSA)
-INITIALIZE_PASS_DEPENDENCY(ScalarEvolutionWrapperPass)
 INITIALIZE_PASS_DEPENDENCY(BranchProbabilityInfoWrapperPass)
+INITIALIZE_PASS_DEPENDENCY(LoopPass)
 INITIALIZE_PASS_END(InductiveRangeCheckElimination, "irce",
                     "Inductive range check elimination", false, false)
 
 const char *InductiveRangeCheck::rangeCheckKindToStr(
     InductiveRangeCheck::RangeCheckKind RCK) {
   switch (RCK) {
   case InductiveRangeCheck::RANGE_CHECK_UNKNOWN:
     return "RANGE_CHECK_UNKNOWN";

lib/Transforms/Scalar/LICM.cpp

struct LICM : public LoopPass {
 
     bool runOnLoop(Loop *L, LPPassManager &LPM) override;
 
     /// This transformation requires natural loop information & requires that
     /// loop preheaders be inserted into the CFG...
     ///
     void getAnalysisUsage(AnalysisUsage &AU) const override {
       AU.setPreservesCFG();
-      AU.addRequired<DominatorTreeWrapperPass>();
-      AU.addRequired<LoopInfoWrapperPass>();
-      AU.addRequiredID(LoopSimplifyID);
-      AU.addPreservedID(LoopSimplifyID);
-      AU.addRequiredID(LCSSAID);
-      AU.addPreservedID(LCSSAID);
-      AU.addRequired<AAResultsWrapperPass>();
-      AU.addPreserved<AAResultsWrapperPass>();
-      AU.addPreserved<BasicAAWrapperPass>();
-      AU.addPreserved<GlobalsAAWrapperPass>();
-      AU.addPreserved<ScalarEvolutionWrapperPass>();
-      AU.addPreserved<SCEVAAWrapperPass>();
       AU.addRequired<TargetLibraryInfoWrapperPass>();
+      getLoopAnalysisUsage(AU);
     }
 
     using llvm::Pass::doFinalization;
 
     bool doFinalization() override {
       assert(LoopToAliasSetMap.empty() && "Didn't free loop alias sets");
       return false;
     }
private:
     /// info from all subloops of L, but does not include instructions in L
     /// itself.
     AliasSetTracker *collectAliasInfoFromSubLoops(Loop *L);
   };
 }
 
 char LICM::ID = 0;
 INITIALIZE_PASS_BEGIN(LICM, "licm", "Loop Invariant Code Motion", false, false)
-INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
-INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)
-INITIALIZE_PASS_DEPENDENCY(LoopSimplify)
-INITIALIZE_PASS_DEPENDENCY(LCSSA)
-INITIALIZE_PASS_DEPENDENCY(ScalarEvolutionWrapperPass)
+INITIALIZE_PASS_DEPENDENCY(LoopPass)
 INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
-INITIALIZE_PASS_DEPENDENCY(BasicAAWrapperPass)
-INITIALIZE_PASS_DEPENDENCY(AAResultsWrapperPass)
-INITIALIZE_PASS_DEPENDENCY(GlobalsAAWrapperPass)
-INITIALIZE_PASS_DEPENDENCY(SCEVAAWrapperPass)
 INITIALIZE_PASS_END(LICM, "licm", "Loop Invariant Code Motion", false, false)
 
 Pass *llvm::createLICMPass() { return new LICM(); }
 
 /// Hoist expressions out of the specified loop. Note, alias info for inner
 /// loop is not preserved so it is not a good idea to run LICM multiple
 /// times on one loop.
 ///

lib/Transforms/Scalar/LoopDeletion.cpp

 
 #include "llvm/Transforms/Scalar.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/Statistic.h"
 #include "llvm/Analysis/GlobalsModRef.h"
 #include "llvm/Analysis/LoopPass.h"
 #include "llvm/Analysis/ScalarEvolution.h"
 #include "llvm/IR/Dominators.h"
+#include "llvm/Transforms/Utils/LoopUtils.h"
 using namespace llvm;
 
 #define DEBUG_TYPE "loop-delete"
 
 STATISTIC(NumDeleted, "Number of loops deleted");
 
 namespace {
   class LoopDeletion : public LoopPass {
   public:
     static char ID; // Pass ID, replacement for typeid
     LoopDeletion() : LoopPass(ID) {
       initializeLoopDeletionPass(*PassRegistry::getPassRegistry());
     }
 
     // Possibly eliminate loop L if it is dead.
     bool runOnLoop(Loop *L, LPPassManager &) override;
 
     void getAnalysisUsage(AnalysisUsage &AU) const override {
-      AU.addRequired<DominatorTreeWrapperPass>();
-      AU.addRequired<LoopInfoWrapperPass>();
-      AU.addRequired<ScalarEvolutionWrapperPass>();
-      AU.addRequiredID(LoopSimplifyID);
-      AU.addRequiredID(LCSSAID);
-
-      AU.addPreserved<ScalarEvolutionWrapperPass>();
-      AU.addPreserved<DominatorTreeWrapperPass>();
-      AU.addPreserved<LoopInfoWrapperPass>();
-      AU.addPreserved<GlobalsAAWrapperPass>();
-      AU.addPreservedID(LoopSimplifyID);
-      AU.addPreservedID(LCSSAID);
+      getLoopAnalysisUsage(AU);
     }
 
   private:
     bool isLoopDead(Loop *L, SmallVectorImpl<BasicBlock *> &exitingBlocks,
                     SmallVectorImpl<BasicBlock *> &exitBlocks,
                     bool &Changed, BasicBlock *Preheader);
 
   };
 }
 
 char LoopDeletion::ID = 0;
 INITIALIZE_PASS_BEGIN(LoopDeletion, "loop-deletion",
                 "Delete dead loops", false, false)
-INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
-INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)
-INITIALIZE_PASS_DEPENDENCY(ScalarEvolutionWrapperPass)
-INITIALIZE_PASS_DEPENDENCY(LoopSimplify)
-INITIALIZE_PASS_DEPENDENCY(LCSSA)
+INITIALIZE_PASS_DEPENDENCY(LoopPass)
 INITIALIZE_PASS_END(LoopDeletion, "loop-deletion",
                 "Delete dead loops", false, false)
 
 Pass *llvm::createLoopDeletionPass() {
   return new LoopDeletion();
 }
 
 /// isLoopDead - Determined if a loop is dead.  This assumes that we've already

lib/Transforms/Scalar/LoopIdiomRecognize.cpp

 #include "llvm/IR/DataLayout.h"
 #include "llvm/IR/Dominators.h"
 #include "llvm/IR/IRBuilder.h"
 #include "llvm/IR/IntrinsicInst.h"
 #include "llvm/IR/Module.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/raw_ostream.h"
 #include "llvm/Transforms/Utils/Local.h"
+#include "llvm/Transforms/Utils/LoopUtils.h"
 using namespace llvm;
 
 #define DEBUG_TYPE "loop-idiom"
 
 STATISTIC(NumMemSet, "Number of memset's formed from loop stores");
 STATISTIC(NumMemCpy, "Number of memcpy's formed from loop load+stores");
 
 namespace {
public:
   }
 
   bool runOnLoop(Loop *L, LPPassManager &LPM) override;
 
   /// This transformation requires natural loop information & requires that
   /// loop preheaders be inserted into the CFG.
   ///
   void getAnalysisUsage(AnalysisUsage &AU) const override {
-    AU.addRequired<LoopInfoWrapperPass>();
-    AU.addPreserved<LoopInfoWrapperPass>();
-    AU.addRequiredID(LoopSimplifyID);
-    AU.addPreservedID(LoopSimplifyID);
-    AU.addRequiredID(LCSSAID);
-    AU.addPreservedID(LCSSAID);
-    AU.addRequired<AAResultsWrapperPass>();
-    AU.addPreserved<AAResultsWrapperPass>();
-    AU.addRequired<ScalarEvolutionWrapperPass>();
-    AU.addPreserved<ScalarEvolutionWrapperPass>();
-    AU.addPreserved<SCEVAAWrapperPass>();
-    AU.addRequired<DominatorTreeWrapperPass>();
-    AU.addPreserved<DominatorTreeWrapperPass>();
     AU.addRequired<TargetLibraryInfoWrapperPass>();
     AU.addRequired<TargetTransformInfoWrapperPass>();
-    AU.addPreserved<BasicAAWrapperPass>();
-    AU.addPreserved<GlobalsAAWrapperPass>();
+    getLoopAnalysisUsage(AU);
   }
 
 private:
   typedef SmallVector<StoreInst *, 8> StoreList;
   typedef MapVector<Value *, StoreList> StoreListMap;
   StoreListMap StoreRefsForMemset;
   StoreListMap StoreRefsForMemsetPattern;
   StoreList StoreRefsForMemcpy;
private:
   /// @}
 };
 
 } // End anonymous namespace.
 
 char LoopIdiomRecognize::ID = 0;
 INITIALIZE_PASS_BEGIN(LoopIdiomRecognize, "loop-idiom", "Recognize loop idioms",
                       false, false)
-INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)
-INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
-INITIALIZE_PASS_DEPENDENCY(LoopSimplify)
-INITIALIZE_PASS_DEPENDENCY(LCSSA)
-INITIALIZE_PASS_DEPENDENCY(ScalarEvolutionWrapperPass)
+INITIALIZE_PASS_DEPENDENCY(LoopPass)
 INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
-INITIALIZE_PASS_DEPENDENCY(BasicAAWrapperPass)
-INITIALIZE_PASS_DEPENDENCY(AAResultsWrapperPass)
-INITIALIZE_PASS_DEPENDENCY(GlobalsAAWrapperPass)
-INITIALIZE_PASS_DEPENDENCY(SCEVAAWrapperPass)
 INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass)
 INITIALIZE_PASS_END(LoopIdiomRecognize, "loop-idiom", "Recognize loop idioms",
                     false, false)
 
 Pass *llvm::createLoopIdiomPass() { return new LoopIdiomRecognize(); }
 
 /// deleteDeadInstruction - Delete this instruction.  Before we do, go through
 /// and zero out all the operands of this instruction.  If any of them become

lib/Transforms/Scalar/LoopInstSimplify.cpp

 #include "llvm/Analysis/LoopPass.h"
 #include "llvm/Analysis/ScalarEvolution.h"
 #include "llvm/IR/DataLayout.h"
 #include "llvm/IR/Dominators.h"
 #include "llvm/IR/Instructions.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Analysis/TargetLibraryInfo.h"
 #include "llvm/Transforms/Utils/Local.h"
+#include "llvm/Transforms/Utils/LoopUtils.h"
 using namespace llvm;
 
 #define DEBUG_TYPE "loop-instsimplify"
 
 STATISTIC(NumSimplified, "Number of redundant instructions simplified");
 
 namespace {
   class LoopInstSimplify : public LoopPass {
   public:
     static char ID; // Pass ID, replacement for typeid
     LoopInstSimplify() : LoopPass(ID) {
       initializeLoopInstSimplifyPass(*PassRegistry::getPassRegistry());
     }
 
     bool runOnLoop(Loop*, LPPassManager&) override;
 
     void getAnalysisUsage(AnalysisUsage &AU) const override {
-      AU.setPreservesCFG();
       AU.addRequired<AssumptionCacheTracker>();
-      AU.addRequired<LoopInfoWrapperPass>();
-      AU.addRequiredID(LoopSimplifyID);
-      AU.addPreservedID(LoopSimplifyID);
-      AU.addPreservedID(LCSSAID);
-      AU.addPreserved<ScalarEvolutionWrapperPass>();
       AU.addRequired<TargetLibraryInfoWrapperPass>();
+      AU.setPreservesCFG();
+      getLoopAnalysisUsage(AU);
     }
   };
 }
 
 char LoopInstSimplify::ID = 0;
 INITIALIZE_PASS_BEGIN(LoopInstSimplify, "loop-instsimplify",
                 "Simplify instructions in loops", false, false)
 INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
+INITIALIZE_PASS_DEPENDENCY(LoopPass)
 INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
-INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
-INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)
-INITIALIZE_PASS_DEPENDENCY(LCSSA)
 INITIALIZE_PASS_END(LoopInstSimplify, "loop-instsimplify",
                 "Simplify instructions in loops", false, false)
 
 Pass *llvm::createLoopInstSimplifyPass() {
   return new LoopInstSimplify();
 }
 
 bool LoopInstSimplify::runOnLoop(Loop *L, LPPassManager &LPM) {

lib/Transforms/Scalar/LoopRerollPass.cpp

public:
     static char ID; // Pass ID, replacement for typeid
     LoopReroll() : LoopPass(ID) {
       initializeLoopRerollPass(*PassRegistry::getPassRegistry());
     }
 
     bool runOnLoop(Loop *L, LPPassManager &LPM) override;
 
     void getAnalysisUsage(AnalysisUsage &AU) const override {
-      AU.addRequired<AAResultsWrapperPass>();
-      AU.addRequired<LoopInfoWrapperPass>();
-      AU.addPreserved<LoopInfoWrapperPass>();
-      AU.addRequired<DominatorTreeWrapperPass>();
-      AU.addPreserved<DominatorTreeWrapperPass>();
-      AU.addRequired<ScalarEvolutionWrapperPass>();
       AU.addRequired<TargetLibraryInfoWrapperPass>();
+      getLoopAnalysisUsage(AU);
     }
 
   protected:
     AliasAnalysis *AA;
     LoopInfo *LI;
     ScalarEvolution *SE;
     TargetLibraryInfo *TLI;
     DominatorTree *DT;
void collectPossibleReductions(Loop *L,
            ReductionTracker &Reductions);
     bool reroll(Instruction *IV, Loop *L, BasicBlock *Header, const SCEV *IterCount,
                 ReductionTracker &Reductions);
   };
 }
 
 char LoopReroll::ID = 0;
 INITIALIZE_PASS_BEGIN(LoopReroll, "loop-reroll", "Reroll loops", false, false)
-INITIALIZE_PASS_DEPENDENCY(AAResultsWrapperPass)
-INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)
-INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
-INITIALIZE_PASS_DEPENDENCY(ScalarEvolutionWrapperPass)
+INITIALIZE_PASS_DEPENDENCY(LoopPass)
 INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
 INITIALIZE_PASS_END(LoopReroll, "loop-reroll", "Reroll loops", false, false)
 
 Pass *llvm::createLoopRerollPass() {
   return new LoopReroll;
 }
 
 // Returns true if the provided instruction is used outside the given loop.

lib/Transforms/Scalar/LoopRotation.cpp

 #include "llvm/IR/Function.h"
 #include "llvm/IR/IntrinsicInst.h"
 #include "llvm/IR/Module.h"
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/raw_ostream.h"
 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
 #include "llvm/Transforms/Utils/Local.h"
+#include "llvm/Transforms/Utils/LoopUtils.h"
 #include "llvm/Transforms/Utils/SSAUpdater.h"
 #include "llvm/Transforms/Utils/ValueMapper.h"
 using namespace llvm;
 
 #define DEBUG_TYPE "loop-rotate"
 
 static cl::opt<unsigned>
 DefaultRotationThreshold("rotation-max-header-size", cl::init(16), cl::Hidden,
LoopRotate(int SpecifiedMaxHeaderSize = -1) : LoopPass(ID) {
     if (SpecifiedMaxHeaderSize == -1)
       MaxHeaderSize = DefaultRotationThreshold;
     else
       MaxHeaderSize = unsigned(SpecifiedMaxHeaderSize);
   }
 
   // LCSSA form makes instruction renaming easier.
   void getAnalysisUsage(AnalysisUsage &AU) const override {
-    AU.addPreserved<AAResultsWrapperPass>();
     AU.addRequired<AssumptionCacheTracker>();
-    AU.addPreserved<DominatorTreeWrapperPass>();
-    AU.addRequired<LoopInfoWrapperPass>();
-    AU.addPreserved<LoopInfoWrapperPass>();
-    AU.addRequiredID(LoopSimplifyID);
-    AU.addPreservedID(LoopSimplifyID);
-    AU.addRequiredID(LCSSAID);
-    AU.addPreservedID(LCSSAID);
-    AU.addPreserved<ScalarEvolutionWrapperPass>();
-    AU.addPreserved<SCEVAAWrapperPass>();
     AU.addRequired<TargetTransformInfoWrapperPass>();
-    AU.addPreserved<BasicAAWrapperPass>();
-    AU.addPreserved<GlobalsAAWrapperPass>();
+    getLoopAnalysisUsage(AU);
   }
 
   bool runOnLoop(Loop *L, LPPassManager &LPM) override {
     if (skipOptnoneFunction(L))
       return false;
     Function &F = *L->getHeader()->getParent();
 
     auto *LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
     const auto *TTI = &getAnalysis<TargetTransformInfoWrapperPass>().getTTI(F);
     auto *AC = &getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
     auto *DTWP = getAnalysisIfAvailable<DominatorTreeWrapperPass>();
     auto *DT = DTWP ? &DTWP->getDomTree() : nullptr;
     auto *SEWP = getAnalysisIfAvailable<ScalarEvolutionWrapperPass>();
     auto *SE = SEWP ? &SEWP->getSE() : nullptr;
 
     return iterativelyRotateLoop(L, MaxHeaderSize, LI, TTI, AC, DT, SE);
   }
 };
 }
 
 char LoopRotate::ID = 0;
 INITIALIZE_PASS_BEGIN(LoopRotate, "loop-rotate", "Rotate Loops", false, false)
-INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass)
 INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
-INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)
-INITIALIZE_PASS_DEPENDENCY(LoopSimplify)
-INITIALIZE_PASS_DEPENDENCY(LCSSA)
-INITIALIZE_PASS_DEPENDENCY(SCEVAAWrapperPass)
-INITIALIZE_PASS_DEPENDENCY(BasicAAWrapperPass)
-INITIALIZE_PASS_DEPENDENCY(GlobalsAAWrapperPass)
+INITIALIZE_PASS_DEPENDENCY(LoopPass)
+INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass)
 INITIALIZE_PASS_END(LoopRotate, "loop-rotate", "Rotate Loops", false, false)
 
 Pass *llvm::createLoopRotatePass(int MaxHeaderSize) {
   return new LoopRotate(MaxHeaderSize);
 }

lib/Transforms/Scalar/LoopSimplifyCFG.cpp

 #include "llvm/Analysis/GlobalsModRef.h"
 #include "llvm/Analysis/LoopInfo.h"
 #include "llvm/Analysis/LoopPass.h"
 #include "llvm/Analysis/ScalarEvolution.h"
 #include "llvm/Analysis/ScalarEvolutionAliasAnalysis.h"
 #include "llvm/Analysis/TargetTransformInfo.h"
 #include "llvm/IR/Dominators.h"
 #include "llvm/Transforms/Utils/Local.h"
+#include "llvm/Transforms/Utils/LoopUtils.h"
 using namespace llvm;
 
 #define DEBUG_TYPE "loop-simplifycfg"
 
 namespace {
 class LoopSimplifyCFG : public LoopPass {
 public:
   static char ID; // Pass ID, replacement for typeid
   LoopSimplifyCFG() : LoopPass(ID) {
     initializeLoopSimplifyCFGPass(*PassRegistry::getPassRegistry());
   }
 
   bool runOnLoop(Loop *L, LPPassManager &) override;
 
   void getAnalysisUsage(AnalysisUsage &AU) const override {
-    AU.addRequired<DominatorTreeWrapperPass>();
-    AU.addRequired<LoopInfoWrapperPass>();
-
-    AU.addPreserved<DominatorTreeWrapperPass>();
-    AU.addPreserved<LoopInfoWrapperPass>();
-    AU.addPreserved<GlobalsAAWrapperPass>();
-    AU.addPreserved<BasicAAWrapperPass>();
-    AU.addPreserved<AAResultsWrapperPass>();
-    AU.addPreserved<ScalarEvolutionWrapperPass>();
-    AU.addPreserved<SCEVAAWrapperPass>();
     AU.addPreserved<DependenceAnalysis>();
-    AU.addPreservedID(LoopSimplifyID);
-    AU.addPreservedID(LCSSAID);
+    getLoopAnalysisUsage(AU);
   }
 };
 }
 
 char LoopSimplifyCFG::ID = 0;
 INITIALIZE_PASS_BEGIN(LoopSimplifyCFG, "loop-simplifycfg", "Simplify loop CFG",
                       false, false)
-INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
-INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)
+INITIALIZE_PASS_DEPENDENCY(LoopPass)
 INITIALIZE_PASS_END(LoopSimplifyCFG, "loop-simplifycfg", "Simplify loop CFG",
                     false, false)
 
 Pass *llvm::createLoopSimplifyCFGPass() { return new LoopSimplifyCFG(); }
 
 static bool simplifyLoopCFG(Loop *L, DominatorTree *DT, LoopInfo *LI) {
   bool Changed = false;
   // Copy blocks into a temporary array to avoid iterator invalidation issues

lib/Transforms/Scalar/LoopUnrollPass.cpp

 #include "llvm/IR/DiagnosticInfo.h"
 #include "llvm/IR/Dominators.h"
 #include "llvm/IR/InstVisitor.h"
 #include "llvm/IR/IntrinsicInst.h"
 #include "llvm/IR/Metadata.h"
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/raw_ostream.h"
+#include "llvm/Transforms/Utils/LoopUtils.h"
 #include "llvm/Transforms/Utils/UnrollLoop.h"
 #include <climits>
 
 using namespace llvm;
 
 #define DEBUG_TYPE "loop-unroll"
 
 static cl::opt<unsigned>
return tryToUnrollLoop(L, DT, LI, SE, TTI, AC, PreserveLCSSA, ProvidedCount,
                            ProvidedRuntime);
   }
 
   /// This transformation requires natural loop information & requires that
   /// loop preheaders be inserted into the CFG...
   ///
   void getAnalysisUsage(AnalysisUsage &AU) const override {
     AU.addRequired<AssumptionCacheTracker>();
-    AU.addRequired<DominatorTreeWrapperPass>();
-    AU.addRequired<LoopInfoWrapperPass>();
-    AU.addPreserved<LoopInfoWrapperPass>();
-    AU.addRequiredID(LoopSimplifyID);
-    AU.addPreservedID(LoopSimplifyID);
-    AU.addRequiredID(LCSSAID);
-    AU.addPreservedID(LCSSAID);
-    AU.addRequired<ScalarEvolutionWrapperPass>();
-    AU.addPreserved<ScalarEvolutionWrapperPass>();
     AU.addRequired<TargetTransformInfoWrapperPass>();
-    // FIXME: Loop unroll requires LCSSA. And LCSSA requires dom info.
-    // If loop unroll does not preserve dom info then LCSSA pass on next
-    // loop will receive invalid dom info.
-    // For now, recreate dom info, if loop is unrolled.
-    AU.addPreserved<DominatorTreeWrapperPass>();
-    AU.addPreserved<GlobalsAAWrapperPass>();
+    // FIXME: Loop passes are required to preserve domtree, and for now we just
+    // recreate dom info if anything gets unrolled.
+    getLoopAnalysisUsage(AU);
   }
 };
 }
 
 char LoopUnroll::ID = 0;
 INITIALIZE_PASS_BEGIN(LoopUnroll, "loop-unroll", "Unroll loops", false, false)
-INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass)
 INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
-INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
-INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)
-INITIALIZE_PASS_DEPENDENCY(LoopSimplify)
-INITIALIZE_PASS_DEPENDENCY(LCSSA)
-INITIALIZE_PASS_DEPENDENCY(ScalarEvolutionWrapperPass)
+INITIALIZE_PASS_DEPENDENCY(LoopPass)
+INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass)
 INITIALIZE_PASS_END(LoopUnroll, "loop-unroll", "Unroll loops", false, false)
 
 Pass *llvm::createLoopUnrollPass(int Threshold, int Count, int AllowPartial,
                                  int Runtime) {
   // TODO: It would make more sense for this function to take the optionals
   // directly, but that's dangerous since it would silently break out of tree
   // callers.
   return new LoopUnroll(Threshold == -1 ? None : Optional<unsigned>(Threshold),

lib/Transforms/Scalar/LoopUnswitch.cpp

 #include "llvm/IR/Module.h"
 #include "llvm/IR/MDBuilder.h"
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/raw_ostream.h"
 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
 #include "llvm/Transforms/Utils/Cloning.h"
 #include "llvm/Transforms/Utils/Local.h"
+#include "llvm/Transforms/Utils/LoopUtils.h"
 #include <algorithm>
 #include <map>
 #include <set>
 using namespace llvm;
 
 #define DEBUG_TYPE "loop-unswitch"
 
 STATISTIC(NumBranches, "Number of branches unswitched");
public:
     bool runOnLoop(Loop *L, LPPassManager &LPM) override;
     bool processCurrentLoop();
 
     /// This transformation requires natural loop information & requires that
     /// loop preheaders be inserted into the CFG.
     ///
     void getAnalysisUsage(AnalysisUsage &AU) const override {
       AU.addRequired<AssumptionCacheTracker>();
-      AU.addRequiredID(LoopSimplifyID);
-      AU.addPreservedID(LoopSimplifyID);
-      AU.addRequired<LoopInfoWrapperPass>();
-      AU.addPreserved<LoopInfoWrapperPass>();
-      AU.addRequiredID(LCSSAID);
-      AU.addPreservedID(LCSSAID);
-      AU.addRequired<DominatorTreeWrapperPass>();
-      AU.addPreserved<DominatorTreeWrapperPass>();
-      AU.addPreserved<ScalarEvolutionWrapperPass>();
       AU.addRequired<TargetTransformInfoWrapperPass>();
-      AU.addPreserved<GlobalsAAWrapperPass>();
+      getLoopAnalysisUsage(AU);
     }
 
   private:
 
     void releaseMemory() override {
       BranchesInfo.forgetLoop(currentLoop);
     }
 
for (UnswitchedValsIt I = Insts.begin(); I != Insts.end(); ++I) {
 
     NewLoopProps.UnswitchedVals[NewInst] = OldLoopProps.UnswitchedVals[OldInst];
   }
 }
 
 char LoopUnswitch::ID = 0;
 INITIALIZE_PASS_BEGIN(LoopUnswitch, "loop-unswitch", "Unswitch loops",
                       false, false)
-INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass)
 INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
-INITIALIZE_PASS_DEPENDENCY(LoopSimplify)
-INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)
-INITIALIZE_PASS_DEPENDENCY(LCSSA)
+INITIALIZE_PASS_DEPENDENCY(LoopPass)
+INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass)
 INITIALIZE_PASS_END(LoopUnswitch, "loop-unswitch", "Unswitch loops",
                       false, false)
 
 Pass *llvm::createLoopUnswitchPass(bool Os) {
   return new LoopUnswitch(Os);
 }
 
 /// Cond is a condition that occurs in L. If it is invariant in the loop, or has

lib/Transforms/Utils/LoopUtils.cpp

 //===-- LoopUtils.cpp - Loop Utility functions -------------------------===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 //
 // This file defines common loop utility functions.
 //
 //===----------------------------------------------------------------------===//
 
+#include "llvm/Analysis/AliasAnalysis.h"
+#include "llvm/Analysis/BasicAliasAnalysis.h"
 #include "llvm/Analysis/LoopInfo.h"
+#include "llvm/Analysis/GlobalsModRef.h"
 #include "llvm/Analysis/ScalarEvolution.h"
 #include "llvm/Analysis/ScalarEvolutionExpressions.h"
+#include "llvm/Analysis/ScalarEvolutionAliasAnalysis.h"
+#include "llvm/IR/Dominators.h"
 #include "llvm/IR/Instructions.h"
 #include "llvm/IR/Module.h"
 #include "llvm/IR/PatternMatch.h"
 #include "llvm/IR/ValueHandle.h"
+#include "llvm/Pass.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Transforms/Utils/LoopUtils.h"
 
 using namespace llvm;
 using namespace llvm::PatternMatch;
 
 #define DEBUG_TYPE "loop-utils"
 
for (auto &Inst : *Block) {
             auto *Use = cast<Instruction>(U);
             return !L->contains(Use->getParent());
           }))
         UsedOutside.push_back(&Inst);
     }
 
   return UsedOutside;
 }
+
+void llvm::getLoopAnalysisUsage(AnalysisUsage &AU) {
+  // By definition, all loop passes need the LoopInfo analysis and the
+  // Dominator tree it depends on. Because they all participate in the loop
+  // pass manager, they must also preserve these.
+  AU.addRequired<DominatorTreeWrapperPass>();
+  AU.addPreserved<DominatorTreeWrapperPass>();
+  AU.addRequired<LoopInfoWrapperPass>();
+  AU.addPreserved<LoopInfoWrapperPass>();
+
+  // We must also preserve LoopSimplify and LCSSA. We locally access their IDs
+  // here because users shouldn't directly get them from this header.
+  extern char &LoopSimplifyID;
+  extern char &LCSSAID;
+  AU.addRequiredID(LoopSimplifyID);
+  AU.addPreservedID(LoopSimplifyID);
+  AU.addRequiredID(LCSSAID);
+  AU.addPreservedID(LCSSAID);
+
+  // Loop passes are designed to run inside of a loop pass manager which means
+  // that any function analyses they require must be required by the first loop
+  // pass in the manager (so that it is computed before the loop pass manager
+  // runs) and preserved by all loop pasess in the manager. To make this
+  // reasonably robust, the set needed for most loop passes is maintained here.
+  // If your loop pass requires an ananalysis not listed here, you will need to
+  // carefully audit the loop pass manager nesting structure that results.
+  AU.addRequired<AAResultsWrapperPass>();
+  AU.addPreserved<AAResultsWrapperPass>();
+  AU.addPreserved<BasicAAWrapperPass>();
+  AU.addPreserved<GlobalsAAWrapperPass>();
+  AU.addPreserved<SCEVAAWrapperPass>();
+  AU.addRequired<ScalarEvolutionWrapperPass>();
+  AU.addPreserved<ScalarEvolutionWrapperPass>();
+}
+
+/// Manually defined geniric "LoopPass" dependncy initialization. This is used
+/// to initialize the exact set of passes from above in \c
+/// getLoopAnalysisUsage. It can be used within a loop pass's initialization
+/// with:
+///
+///   INITIALIZE_PASS_DEPENDENCY(LoopPass)
+///
+/// As-if "LoopPass" were a pass.
+void llvm::initializeLoopPassPass(PassRegistry &Registry) {
+  INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
+  INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)
+  INITIALIZE_PASS_DEPENDENCY(LoopSimplify)
+  INITIALIZE_PASS_DEPENDENCY(LCSSA)
+  INITIALIZE_PASS_DEPENDENCY(AAResultsWrapperPass)
+  INITIALIZE_PASS_DEPENDENCY(BasicAAWrapperPass)
+  INITIALIZE_PASS_DEPENDENCY(GlobalsAAWrapperPass)
+  INITIALIZE_PASS_DEPENDENCY(SCEVAAWrapperPass)
+  INITIALIZE_PASS_DEPENDENCY(ScalarEvolutionWrapperPass)
+}

test/Other/pass-pipelines.ll

 ; CHECK-O2-NEXT: Function Integration/Inlining
 ; CHECK-O2-NEXT: Deduce function attributes
 ; Next up is the main function pass pipeline. It shouldn't be split up and
 ; should contain the main loop pass pipeline as well.
 ; CHECK-O2-NEXT: FunctionPass Manager
 ; CHECK-O2-NOT: Manager
 ; CHECK-O2: Loop Pass Manager
 ; CHECK-O2-NOT: Manager
-; FIXME: We shouldn't have this extra loop pass manager!
-; CHECK-O2: Loop Pass Manager
-; CHECK-O2-NOT: Manager
-; FIXME: Yet another pointless loop pass manager!
-; CHECK-O2: Loop Pass Manager
-; CHECK-O2-NOT: Manager
 ; FIXME: We shouldn't be pulling out to simplify-cfg and instcombine and
 ; causing new loop pass managers.
 ; CHECK-O2: Simplify the CFG
 ; CHECK-O2-NOT: Manager
 ; CHECK-O2: Combine redundant instructions
 ; CHECK-O2-NOT: Manager
 ; CHECK-O2: Loop Pass Manager
 ; CHECK-O2-NOT: Manager
-; FIXME: Yet another pointless loop pass manager!
-; CHECK-O2: Loop Pass Manager
-; CHECK-O2-NOT: Manager
-; FIXME: Yet another pointless loop pass manager!
-; CHECK-O2: Loop Pass Manager
-; CHECK-O2-NOT: Manager
 ; FIXME: It isn't clear that we need yet another loop pass pipeline
 ; and run of LICM here.
 ; CHECK-O2-NOT: Manager
 ; CHECK-O2: Loop Pass Manager
 ; CHECK-O2-NEXT: Loop Invariant Code Motion
 ; CHECK-O2-NOT: Manager
 ; Next we break out of the main Function passes inside the CGSCC pipeline with
 ; a barrier pass.

test/Transforms/LoopReroll/nonconst_lb.ll

 ; CHECK:   %1 = sub i32 %0, %m
 ; CHECK:   %2 = lshr i32 %1, 2
 ; CHECK:   %3 = shl i32 %2, 2
 ; CHECK:   %4 = add i32 %m, %3
 ; CHECK:   %5 = add i32 %4, 3
 ; CHECK:   br label %for.body
 
 ; CHECK: for.body:                                         ; preds = %for.body, %for.body.preheader
-; CHECK:   %indvar = phi i32 [ %indvar.next, %for.body ], [ 0, %for.body.preheader ]
+; CHECK:   %indvar = phi i32 [ 0, %for.body.preheader ], [ %indvar.next, %for.body ]
 ; CHECK:   %6 = add i32 %m, %indvar
 ; CHECK:   %arrayidx = getelementptr inbounds i32, i32* %B, i32 %6
 ; CHECK:   %7 = load i32, i32* %arrayidx, align 4
 ; CHECK:   %mul = shl nsw i32 %7, 2
 ; CHECK:   %arrayidx2 = getelementptr inbounds i32, i32* %A, i32 %6
 ; CHECK:   store i32 %mul, i32* %arrayidx2, align 4
 ; CHECK:   %indvar.next = add i32 %indvar, 1
 ; CHECK:   %exitcond = icmp eq i32 %6, %5
-; CHECK:   br i1 %exitcond, label %for.end, label %for.body
+; CHECK:   br i1 %exitcond, label %for.end.loopexit, label %for.body
 
 ;void daxpy_ur(int n,float da,float *dx,float *dy)
 ;    {
 ;    int m = n % 4;
 ;    for (int i = m; i < n; i = i + 4)
 ;        {
 ;        dy[i]   = dy[i]   + da*dx[i];
 ;        dy[i+1] = dy[i+1] + da*dx[i+1];

 ; CHECK:   %1 = sub i32 %0, %rem
 ; CHECK:   %2 = lshr i32 %1, 2
 ; CHECK:   %3 = shl i32 %2, 2
 ; CHECK:   %4 = add i32 %rem, %3
 ; CHECK:   %5 = add i32 %4, 3
 ; CHECK:   br label %for.body
 
 ; CHECK: for.body:
-; CHECK:   %indvar = phi i32 [ %indvar.next, %for.body ], [ 0, %for.body.preheader ]
+; CHECK:   %indvar = phi i32 [ 0, %for.body.preheader ], [ %indvar.next, %for.body ]
 ; CHECK:   %6 = add i32 %rem, %indvar
 ; CHECK:   %arrayidx = getelementptr inbounds float, float* %dy, i32 %6
 ; CHECK:   %7 = load float, float* %arrayidx, align 4
 ; CHECK:   %arrayidx1 = getelementptr inbounds float, float* %dx, i32 %6
 ; CHECK:   %8 = load float, float* %arrayidx1, align 4
 ; CHECK:   %mul = fmul float %8, %da
 ; CHECK:   %add = fadd float %7, %mul
 ; CHECK:   store float %add, float* %arrayidx, align 4
 ; CHECK:   %indvar.next = add i32 %indvar, 1
 ; CHECK:   %exitcond = icmp eq i32 %6, %5
-; CHECK:   br i1 %exitcond, label %for.end, label %for.body
+; CHECK:   br i1 %exitcond, label %for.end.loopexit, label %for.body