[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

1 files changed, 60 insertions, 0 deletions

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)
+}