[PATCH] D21237: LoopRotation: remove iterative calls to rotateLoops

[Sebastian Pop via llvm-commits]

sebpop created this revision.
sebpop added reviewers: dberlin, atrick, hfinkel.
sebpop added subscribers: llvm-commits, hiraditya.
Herald added a subscriber: mzolotukhin.

Loops should be rotated only once.  Passes regression test and llvm test-suite.

Patch wrote by Aditya Kumar and Sebastian Pop.

http://reviews.llvm.org/D21237

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

Index: llvm/lib/Transforms/Scalar/LoopRotation.cpp
===================================================================
--- llvm/lib/Transforms/Scalar/LoopRotation.cpp
+++ llvm/lib/Transforms/Scalar/LoopRotation.cpp
@@ -569,9 +569,8 @@
   return true;
 }
 
-/// Rotate \c L as many times as possible. Return true if the loop is rotated
-/// at least once.
-static bool iterativelyRotateLoop(Loop *L, unsigned MaxHeaderSize, LoopInfo *LI,
+/// Rotate loop L.  Return true if the loop is rotated.
+static bool rotateLoop(Loop *L, unsigned MaxHeaderSize, LoopInfo *LI,
                                   const TargetTransformInfo *TTI,
                                   AssumptionCache *AC, DominatorTree *DT,
                                   ScalarEvolution *SE) {
@@ -582,13 +581,8 @@
   // upward. Rotation may not be needed if the loop tail can be folded into the
   // loop exit.
   bool SimplifiedLatch = simplifyLoopLatch(L, LI, DT);
-
-  // One loop can be rotated multiple times.
-  bool MadeChange = false;
-  while (rotateLoop(L, MaxHeaderSize, LI, TTI, AC, DT, SE, SimplifiedLatch)) {
-    MadeChange = true;
-    SimplifiedLatch = false;
-  }
+  bool MadeChange = rotateLoop(L, MaxHeaderSize, LI, TTI, AC, DT, SE,
+                               SimplifiedLatch);
 
   // Restore the loop metadata.
   // NB! We presume LoopRotation DOESN'T ADD its own metadata.
@@ -613,7 +607,7 @@
   auto *DT = FAM.getCachedResult<DominatorTreeAnalysis>(*F);
   auto *SE = FAM.getCachedResult<ScalarEvolutionAnalysis>(*F);
 
-  bool Changed = iterativelyRotateLoop(&L, MaxHeaderSize, LI, TTI, AC, DT, SE);
+  bool Changed = rotateLoop(&L, MaxHeaderSize, LI, TTI, AC, DT, SE);
   if (!Changed)
     return PreservedAnalyses::all();
   return getLoopPassPreservedAnalyses();
@@ -654,7 +648,7 @@
     auto *SEWP = getAnalysisIfAvailable<ScalarEvolutionWrapperPass>();
     auto *SE = SEWP ? &SEWP->getSE() : nullptr;
 
-    return iterativelyRotateLoop(L, MaxHeaderSize, LI, TTI, AC, DT, SE);
+    return rotateLoop(L, MaxHeaderSize, LI, TTI, AC, DT, SE);
   }
 };
 }


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