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

routine.

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.

I've not updated the loop passes using LoopAccessAnalysis because that
analysis hasn't been fully wired into LoopSimplify/LCSSA, and it isn't
clear that those transforms want to support those forms anyways. They
all run late anyways, so this is harmless. Similarly, LSR is left alone
because it already carefully manages its forms and doesn't need to get
fused into a single loop pass manager with a bunch of other loop passes.

LoopReroll didn't use loop simplified form previously, and I've updated
the test case to match the trivially different output.

Finally, I've also factored all the pass initialization for the passes
that use this technique as well, so that should be done regularly and
reliably.

Thanks to James for the help reviewing and thinking about this stuff,
and Ben for help thinking about it as well!

Differential Revision: http://reviews.llvm.org/D17435

llvm-svn: 261316

12 files changed, 95 insertions, 171 deletions

diff --git a/llvm/lib/Transforms/Scalar/IndVarSimplify.cpp b/llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
index 02c2629f6b5..c9dec3b28dc 100644
--- a/llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
+++ b/llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
@@ -107,16 +107,8 @@ public:
   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:
@@ -148,11 +140,7 @@ private:
 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)
 
diff --git a/llvm/lib/Transforms/Scalar/InductiveRangeCheckElimination.cpp b/llvm/lib/Transforms/Scalar/InductiveRangeCheckElimination.cpp
index dea61f6ff3d..590d4c53043 100644
--- a/llvm/lib/Transforms/Scalar/InductiveRangeCheckElimination.cpp
+++ b/llvm/lib/Transforms/Scalar/InductiveRangeCheckElimination.cpp
@@ -211,11 +211,8 @@ public:
   }
 
   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;
@@ -226,11 +223,8 @@ 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)
 
diff --git a/llvm/lib/Transforms/Scalar/LICM.cpp b/llvm/lib/Transforms/Scalar/LICM.cpp
index 3a0615b2221..0e7f534c32a 100644
--- a/llvm/lib/Transforms/Scalar/LICM.cpp
+++ b/llvm/lib/Transforms/Scalar/LICM.cpp
@@ -118,19 +118,8 @@ namespace {
     ///
     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;
@@ -174,16 +163,8 @@ namespace {
 
 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(); }
diff --git a/llvm/lib/Transforms/Scalar/LoopDeletion.cpp b/llvm/lib/Transforms/Scalar/LoopDeletion.cpp
index 7b1940b48c3..498e7d64376 100644
--- a/llvm/lib/Transforms/Scalar/LoopDeletion.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopDeletion.cpp
@@ -21,6 +21,7 @@
 #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"
@@ -39,18 +40,7 @@ namespace {
     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:
@@ -64,11 +54,7 @@ namespace {
 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)
 
diff --git a/llvm/lib/Transforms/Scalar/LoopIdiomRecognize.cpp b/llvm/lib/Transforms/Scalar/LoopIdiomRecognize.cpp
index 85b185b39b5..87439ec9ebe 100644
--- a/llvm/lib/Transforms/Scalar/LoopIdiomRecognize.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopIdiomRecognize.cpp
@@ -54,6 +54,7 @@
 #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"
@@ -85,23 +86,9 @@ public:
   /// 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:
@@ -154,16 +141,8 @@ private:
 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)
diff --git a/llvm/lib/Transforms/Scalar/LoopInstSimplify.cpp b/llvm/lib/Transforms/Scalar/LoopInstSimplify.cpp
index b4102fe9ba3..5847ad261b8 100644
--- a/llvm/lib/Transforms/Scalar/LoopInstSimplify.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopInstSimplify.cpp
@@ -25,6 +25,7 @@
 #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"
@@ -42,14 +43,10 @@ namespace {
     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);
     }
   };
 }
@@ -58,10 +55,8 @@ 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)
 
diff --git a/llvm/lib/Transforms/Scalar/LoopRerollPass.cpp b/llvm/lib/Transforms/Scalar/LoopRerollPass.cpp
index 014bc43363f..9f2aa1e2345 100644
--- a/llvm/lib/Transforms/Scalar/LoopRerollPass.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopRerollPass.cpp
@@ -147,13 +147,8 @@ namespace {
     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:
@@ -439,10 +434,7 @@ namespace {
 
 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)
 
diff --git a/llvm/lib/Transforms/Scalar/LoopRotation.cpp b/llvm/lib/Transforms/Scalar/LoopRotation.cpp
index 14621e51b60..1a9d1db1a53 100644
--- a/llvm/lib/Transforms/Scalar/LoopRotation.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopRotation.cpp
@@ -34,6 +34,7 @@
 #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;
@@ -578,20 +579,9 @@ public:
 
   // 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 {
@@ -614,14 +604,9 @@ public:
 
 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) {
diff --git a/llvm/lib/Transforms/Scalar/LoopSimplifyCFG.cpp b/llvm/lib/Transforms/Scalar/LoopSimplifyCFG.cpp
index b5fdae94c49..a15d1e85691 100644
--- a/llvm/lib/Transforms/Scalar/LoopSimplifyCFG.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopSimplifyCFG.cpp
@@ -29,6 +29,7 @@
 #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"
@@ -44,19 +45,8 @@ public:
   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);
   }
 };
 }
@@ -64,8 +54,7 @@ public:
 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)
 
diff --git a/llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp b/llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp
index 509687ce472..13d089d57df 100644
--- a/llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp
@@ -32,6 +32,7 @@
 #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>
 
@@ -744,35 +745,19 @@ public:
   ///
   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,
diff --git a/llvm/lib/Transforms/Scalar/LoopUnswitch.cpp b/llvm/lib/Transforms/Scalar/LoopUnswitch.cpp
index 95d7f8a3bed..c3b941f46f6 100644
--- a/llvm/lib/Transforms/Scalar/LoopUnswitch.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopUnswitch.cpp
@@ -55,6 +55,7 @@
 #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>
@@ -211,17 +212,8 @@ namespace {
     ///
     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:
@@ -382,11 +374,9 @@ void LUAnalysisCache::cloneData(const Loop *NewLoop, const Loop *OldLoop,
 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)
 
diff --git a/llvm/lib/Transforms/Utils/LoopUtils.cpp b/llvm/lib/Transforms/Utils/LoopUtils.cpp
index fa958e913b7..240fff0d822 100644
--- a/llvm/lib/Transforms/Utils/LoopUtils.cpp
+++ b/llvm/lib/Transforms/Utils/LoopUtils.cpp
@@ -11,13 +11,19 @@
 //
 //===----------------------------------------------------------------------===//
 
+#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"
 
@@ -727,3 +733,57 @@ SmallVector<Instruction *, 8> llvm::findDefsUsedOutsideOfLoop(Loop *L) {
 
   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 analysis 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 generic "LoopPass" dependency 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)
+}