LPM: Simplify how passes mark loops for deletion. NFC

When a pass removes a loop it currently has to reach up into the
LPPassManager's internals to update the state of the iteration over
loops. This reverse dependency results in a pretty awkward interplay
of the LPPassManager and its Passes.

Here, we change this to instead keep track of when a loop has become
"unlooped" in the Loop objects themselves, then the LPPassManager can
check this and manipulate its own state directly. This opens the door
to allow most of the loop passes to work without a backreference to
the LPPassManager.

I've kept passes calling the LPPassManager::deleteLoopFromQueue API
now so I could put an assert in to prove that this is NFC, but a later
pass will update passes just to preserve the LoopInfo directly and
stop referencing the LPPassManager completely.

llvm-svn: 255720

2 files changed, 17 insertions, 42 deletions

diff --git a/llvm/lib/Analysis/LoopInfo.cpp b/llvm/lib/Analysis/LoopInfo.cpp
index 07fd6a2ae70..ee311c50eee 100644
--- a/llvm/lib/Analysis/LoopInfo.cpp
+++ b/llvm/lib/Analysis/LoopInfo.cpp
@@ -630,14 +630,8 @@ LoopInfo::LoopInfo(const DominatorTreeBase<BasicBlock> &DomTree) {
   analyze(DomTree);
 }
 
-/// updateUnloop - The last backedge has been removed from a loop--now the
-/// "unloop". Find a new parent for the blocks contained within unloop and
-/// update the loop tree. We don't necessarily have valid dominators at this
-/// point, but LoopInfo is still valid except for the removal of this loop.
-///
-/// Note that Unloop may now be an empty loop. Calling Loop::getHeader without
-/// checking first is illegal.
 void LoopInfo::updateUnloop(Loop *Unloop) {
+  Unloop->markAsUnloop();
 
   // First handle the special case of no parent loop to simplify the algorithm.
   if (!Unloop->getParentLoop()) {
diff --git a/llvm/lib/Analysis/LoopPass.cpp b/llvm/lib/Analysis/LoopPass.cpp
index 0cfc94c1434..54b61256134 100644
--- a/llvm/lib/Analysis/LoopPass.cpp
+++ b/llvm/lib/Analysis/LoopPass.cpp
@@ -58,37 +58,14 @@ char LPPassManager::ID = 0;
 
 LPPassManager::LPPassManager()
   : FunctionPass(ID), PMDataManager() {
-  skipThisLoop = false;
   LI = nullptr;
   CurrentLoop = nullptr;
 }
 
 /// Delete loop from the loop queue and loop hierarchy (LoopInfo).
 void LPPassManager::deleteLoopFromQueue(Loop *L) {
-
+  assert(CurrentLoop == L && "deleting a loop that is not being operated on");
   LI->updateUnloop(L);
-
-  // Notify passes that the loop is being deleted.
-  deleteSimpleAnalysisLoop(L);
-
-  // If L is current loop then skip rest of the passes and let
-  // runOnFunction remove L from LQ. Otherwise, remove L from LQ now
-  // and continue applying other passes on CurrentLoop.
-  if (CurrentLoop == L)
-    skipThisLoop = true;
-
-  delete L;
-
-  if (skipThisLoop)
-    return;
-
-  for (std::deque<Loop *>::iterator I = LQ.begin(),
-         E = LQ.end(); I != E; ++I) {
-    if (*I == L) {
-      LQ.erase(I);
-      break;
-    }
-  }
 }
 
 // Inset loop into loop nest (LoopInfo) and loop queue (LQ).
@@ -204,9 +181,7 @@ bool LPPassManager::runOnFunction(Function &F) {
   // Walk Loops
   while (!LQ.empty()) {
 
-    CurrentLoop  = LQ.back();
-    skipThisLoop = false;
-
+    CurrentLoop = LQ.back();
     // Run all passes on the current Loop.
     for (unsigned Index = 0; Index < getNumContainedPasses(); ++Index) {
       LoopPass *P = getContainedPass(Index);
@@ -226,11 +201,15 @@ bool LPPassManager::runOnFunction(Function &F) {
 
       if (Changed)
         dumpPassInfo(P, MODIFICATION_MSG, ON_LOOP_MSG,
-                     skipThisLoop ? "<deleted>" :
-                                    CurrentLoop->getHeader()->getName());
+                     CurrentLoop->isUnloop()
+                         ? "<deleted>"
+                         : CurrentLoop->getHeader()->getName());
       dumpPreservedSet(P);
 
-      if (!skipThisLoop) {
+      if (CurrentLoop->isUnloop()) {
+        // Notify passes that the loop is being deleted.
+        deleteSimpleAnalysisLoop(CurrentLoop);
+      } else {
         // Manually check that this loop is still healthy. This is done
         // instead of relying on LoopInfo::verifyLoop since LoopInfo
         // is a function pass and it's really expensive to verify every
@@ -249,12 +228,12 @@ bool LPPassManager::runOnFunction(Function &F) {
 
       removeNotPreservedAnalysis(P);
       recordAvailableAnalysis(P);
-      removeDeadPasses(P,
-                       skipThisLoop ? "<deleted>" :
-                                      CurrentLoop->getHeader()->getName(),
+      removeDeadPasses(P, CurrentLoop->isUnloop()
+                              ? "<deleted>"
+                              : CurrentLoop->getHeader()->getName(),
                        ON_LOOP_MSG);
 
-      if (skipThisLoop)
+      if (CurrentLoop->isUnloop())
         // Do not run other passes on this loop.
         break;
     }
@@ -262,11 +241,13 @@ bool LPPassManager::runOnFunction(Function &F) {
     // If the loop was deleted, release all the loop passes. This frees up
     // some memory, and avoids trouble with the pass manager trying to call
     // verifyAnalysis on them.
-    if (skipThisLoop)
+    if (CurrentLoop->isUnloop()) {
       for (unsigned Index = 0; Index < getNumContainedPasses(); ++Index) {
         Pass *P = getContainedPass(Index);
         freePass(P, "<deleted>", ON_LOOP_MSG);
       }
+      delete CurrentLoop;
+    }
 
     // Pop the loop from queue after running all passes.
     LQ.pop_back();