[PATCH] D74691: [Attributor] add some pattern to containsCycle

[omar ahmed via Phabricator via llvm-commits]

omarahmed updated this revision to Diff 245368.
omarahmed added a comment.

it's a bit messy but is the approach right


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D74691/new/

https://reviews.llvm.org/D74691

Files:
  llvm/lib/Transforms/IPO/Attributor.cpp


Index: llvm/lib/Transforms/IPO/Attributor.cpp
===================================================================
--- llvm/lib/Transforms/IPO/Attributor.cpp
+++ llvm/lib/Transforms/IPO/Attributor.cpp
@@ -2369,14 +2369,42 @@
 // Helper function that checks whether a function has any cycle.
 // TODO: Replace with more efficent code
 static bool containsCycle(Function &F) {
-  SmallPtrSet<BasicBlock *, 32> Visited;
+  bool noAnalysis = false;
 
-  // Traverse BB by dfs and check whether successor is already visited.
-  for (BasicBlock *BB : depth_first(&F)) {
-    Visited.insert(BB);
-    for (auto *SuccBB : successors(BB)) {
-      if (Visited.count(SuccBB))
-        return true;
+  ScalarEvolution *SE =
+      A.getInfoCache().getAnalysisResultForFunction<ScalarEvolutionAnalysis>(F);
+  LoopInfo *LI = A.getInfoCache().getAnalysisResultForFunction<LoopAnalysis>(F);
+
+  if (!LI || !SE) {
+    noAnalysis = true;
+  }
+
+  for (scc_iterator<Function *> I = scc_begin(&F), IE = scc_end(&F); I != IE;
+       ++I) {
+    const std::vector<BasicBlock *> &SCCBBs = *I;
+    // when noAnalysis available then check only if the SCC has loop or not
+    if (noAnalysis) {
+      if (I.hasLoop()) return true;
+      continue;
+    }
+    // when current SCC has a single block with no loop continue to the next SCC
+    if (!I.hasLoop()) continue;
+
+    std::vector<BasicBlock *>::const_iterator BBI = SCCBBs.begin();
+    Loop *L = LI->getLoopFor(*BBI);
+    if (!L) {
+      return true;
+    }
+    if (L->getNumBlocks() > SCCBBs.size()) return true;
+    if (L->getNumBlocks() == SCCBBs.size()) {
+      if (!SE->getSmallConstantMaxTripCount(L)) return true;
+      continue;
+    }
+    L = L->getParentLoop();
+    if (L->getNumBlocks() > SCCBBs.size()) return true;
+    if (L->getNumBlocks() == SCCBBs.size()) {
+      if (!SE->getSmallConstantMaxTripCount(L)) return true;
+      continue;
     }
   }
   return false;


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