[PATCH] D98263: [LoopInterchange] fix tightlyNested() in LoopInterchange legality

[Congzhe Cao via Phabricator via llvm-commits]

congzhe updated this revision to Diff 329349.

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D98263/new/

https://reviews.llvm.org/D98263

Files:
  llvm/lib/Transforms/Scalar/LoopInterchange.cpp


Index: llvm/lib/Transforms/Scalar/LoopInterchange.cpp
===================================================================
--- llvm/lib/Transforms/Scalar/LoopInterchange.cpp
+++ llvm/lib/Transforms/Scalar/LoopInterchange.cpp
@@ -19,6 +19,7 @@
 #include "llvm/ADT/StringRef.h"
 #include "llvm/Analysis/DependenceAnalysis.h"
 #include "llvm/Analysis/LoopInfo.h"
+#include "llvm/Analysis/LoopNestAnalysis.h"
 #include "llvm/Analysis/LoopPass.h"
 #include "llvm/Analysis/OptimizationRemarkEmitter.h"
 #include "llvm/Analysis/ScalarEvolution.h"
@@ -605,6 +606,21 @@
       containsUnsafeInstructions(InnerLoopPreHeader))
     return false;
 
+  BasicBlock *InnerLoopExit = InnerLoop->getExitBlock();
+  // Ensure the inner loop exit block flow to the outer loop latch possibly
+  // through empty blocks
+  const BasicBlock &SuccInner = LoopNest::skipEmptyBlockUntil(InnerLoopExit, OuterLoopLatch);
+  if (&SuccInner != OuterLoopLatch) {
+    LLVM_DEBUG(dbgs() << "Inner loop exit block " << *InnerLoopExit
+                      << " does not lead to the outer loop latch.\n";);
+    return false;
+  }
+  // The inner loop exit block does flow to the outer loop latch and not some
+  // other BBs, now make sure it contains safe instructions, since it will be
+  // move into the (new) inner loop after interchange
+  if (containsUnsafeInstructions(InnerLoopExit))
+    return false;
+
   LLVM_DEBUG(dbgs() << "Loops are perfectly nested\n");
   // We have a perfect loop nest.
   return true;


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