From 58b987211a031ee54a57ce972e81ab8525b2148f Mon Sep 17 00:00:00 2001
From: Max Kazantsev <max.kazantsev@azul.com>
Date: Tue, 19 Feb 2019 11:14:05 +0000
Subject: [PATCH] [NFC] API for signaling that the current loop is being
 deleted

We are planning to be able to delete the current loop in LoopSimplifyCFG
in the future. Add API to notify the loop pass manager that it happened.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@354314 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Transforms/Scalar/LoopSimplifyCFG.cpp | 39 +++++++++++++++++------
 1 file changed, 30 insertions(+), 9 deletions(-)

diff --git a/lib/Transforms/Scalar/LoopSimplifyCFG.cpp b/lib/Transforms/Scalar/LoopSimplifyCFG.cpp
index fd417055f9c..55cf20a2936 100644
--- a/lib/Transforms/Scalar/LoopSimplifyCFG.cpp
+++ b/lib/Transforms/Scalar/LoopSimplifyCFG.cpp
@@ -596,6 +596,10 @@ public:
 
     return true;
   }
+
+  bool foldingBreaksCurrentLoop() const {
+    return DeleteCurrentLoop;
+  }
 };
 } // namespace
 
@@ -603,7 +607,8 @@ public:
 /// branches.
 static bool constantFoldTerminators(Loop &L, DominatorTree &DT, LoopInfo &LI,
                                     ScalarEvolution &SE,
-                                    MemorySSAUpdater *MSSAU) {
+                                    MemorySSAUpdater *MSSAU,
+                                    bool &IsLoopDeleted) {
   if (!EnableTermFolding)
     return false;
 
@@ -613,7 +618,9 @@ static bool constantFoldTerminators(Loop &L, DominatorTree &DT, LoopInfo &LI,
     return false;
 
   ConstantTerminatorFoldingImpl BranchFolder(L, LI, DT, SE, MSSAU);
-  return BranchFolder.run();
+  bool Changed = BranchFolder.run();
+  IsLoopDeleted = Changed && BranchFolder.foldingBreaksCurrentLoop();
+  return Changed;
 }
 
 static bool mergeBlocksIntoPredecessors(Loop &L, DominatorTree &DT,
@@ -645,11 +652,15 @@ static bool mergeBlocksIntoPredecessors(Loop &L, DominatorTree &DT,
 }
 
 static bool simplifyLoopCFG(Loop &L, DominatorTree &DT, LoopInfo &LI,
-                            ScalarEvolution &SE, MemorySSAUpdater *MSSAU) {
+                            ScalarEvolution &SE, MemorySSAUpdater *MSSAU,
+                            bool &isLoopDeleted) {
   bool Changed = false;
 
   // Constant-fold terminators with known constant conditions.
-  Changed |= constantFoldTerminators(L, DT, LI, SE, MSSAU);
+  Changed |= constantFoldTerminators(L, DT, LI, SE, MSSAU, isLoopDeleted);
+
+  if (isLoopDeleted)
+    return true;
 
   // Eliminate unconditional branches by merging blocks into their predecessors.
   Changed |= mergeBlocksIntoPredecessors(L, DT, LI, MSSAU);
@@ -662,14 +673,19 @@ static bool simplifyLoopCFG(Loop &L, DominatorTree &DT, LoopInfo &LI,
 
 PreservedAnalyses LoopSimplifyCFGPass::run(Loop &L, LoopAnalysisManager &AM,
                                            LoopStandardAnalysisResults &AR,
-                                           LPMUpdater &) {
+                                           LPMUpdater &LPMU) {
   Optional<MemorySSAUpdater> MSSAU;
   if (EnableMSSALoopDependency && AR.MSSA)
     MSSAU = MemorySSAUpdater(AR.MSSA);
+  bool DeleteCurrentLoop = false;
   if (!simplifyLoopCFG(L, AR.DT, AR.LI, AR.SE,
-                       MSSAU.hasValue() ? MSSAU.getPointer() : nullptr))
+                       MSSAU.hasValue() ? MSSAU.getPointer() : nullptr,
+                       DeleteCurrentLoop))
     return PreservedAnalyses::all();
 
+  if (DeleteCurrentLoop)
+    LPMU.markLoopAsDeleted(L, "loop-simplifycfg");
+
   return getLoopPassPreservedAnalyses();
 }
 
@@ -681,7 +697,7 @@ public:
     initializeLoopSimplifyCFGLegacyPassPass(*PassRegistry::getPassRegistry());
   }
 
-  bool runOnLoop(Loop *L, LPPassManager &) override {
+  bool runOnLoop(Loop *L, LPPassManager &LPM) override {
     if (skipLoop(L))
       return false;
 
@@ -695,8 +711,13 @@ public:
       if (VerifyMemorySSA)
         MSSA->verifyMemorySSA();
     }
-    return simplifyLoopCFG(*L, DT, LI, SE,
-                           MSSAU.hasValue() ? MSSAU.getPointer() : nullptr);
+    bool DeleteCurrentLoop = false;
+    bool Changed = simplifyLoopCFG(
+        *L, DT, LI, SE, MSSAU.hasValue() ? MSSAU.getPointer() : nullptr,
+        DeleteCurrentLoop);
+    if (DeleteCurrentLoop)
+      LPM.markLoopAsDeleted(*L);
+    return Changed;
   }
 
   void getAnalysisUsage(AnalysisUsage &AU) const override {
-- 
2.40.0