[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

diff --git a/lib/Transforms/Scalar/LoopSimplifyCFG.cpp b/lib/Transforms/Scalar/LoopSimplifyCFG.cpp
index fd417055f9c36a3b44926b73e85fd4d301ace85a..55cf20a2936c041b3a2db466437d5c0134b34bcf 100644 (file)
--- 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 {