LoopOptTutorial: Basic loop optimization template [STEP2]

llvm/include/llvm/Transforms/Scalar/LoopOptTutorial.h

@@ -33,6 +33,10 @@ class LoopSplit {
 
 private:
   LoopInfo &LI;
+
+  /// Determines if \p L is a candidate for splitting
+  bool isCandidate(const Loop &L) const;
+
 };
 
 class LoopOptTutorialPass : public PassInfoMixin<LoopOptTutorialPass> {

llvm/lib/Transforms/Scalar/LoopOptTutorial.cpp

@@ -27,22 +27,50 @@ bool LoopSplit::run(Loop &L) const {
 
   LLVM_DEBUG(dbgs() << "Entering " << __func__ << "\n");
 
-  LLVM_DEBUG(dbgs() << "TODO: Need to check if Loop is a valid candidate\n");
+  if (!isCandidate(L)) {
+    LLVM_DEBUG(dbgs() << "Loop " << L.getName()
+                      << " is not a candidate for splitting.\n");
+    return false;
+  }
+
+  LLVM_DEBUG(dbgs() << "Loop " << L.getName()
+                    << " is a candidate for splitting!\n");
 
   return false;
 }
 
+bool LoopSplit::isCandidate(const Loop &L) const {
+  // Require loops with preheaders and dedicated exits.
+  if (!L.isLoopSimplifyForm())
+    return false;
+
+  // Since we use cloning to split the loop, it has to be safe to clone.
+  if (!L.isSafeToClone())
+    return false;
+
+  // If the loop has multiple exiting blocks, do not split.
+  if (!L.getExitingBlock())
+    return false;
+
+  // If loop has multiple exit blocks, do not split.
+  if (!L.getExitBlock())
+    return false;
+
+  // Only split innermost loops. Thus, if the loop has any children, it cannot
+  // be split.
+  if (!L.getSubLoops().empty())
+    return false;
+
+  return true;
+}
+
 PreservedAnalyses LoopOptTutorialPass::run(Loop &L, LoopAnalysisManager &LAM,
                                            LoopStandardAnalysisResults &AR,
                                            LPMUpdater &U) {
-  bool Changed = false;
-
   LLVM_DEBUG(dbgs() << "Entering LoopOptTutorialPass::run\n");
   LLVM_DEBUG(dbgs() << "Loop: "; L.dump(); dbgs() << "\n");
 
-  LoopSplit LS(AR.LI);
-
-  Changed = LS.run(L);
+  bool Changed = LoopSplit(AR.LI).run(L);
 
   if (!Changed)
     return PreservedAnalyses::all();