[llvm] r255133 - Revert "Revert r253253 and r253126: "Don't recompute LCSSA after loop-unrolling when possible.""

[Michael Zolotukhin via llvm-commits]

Author: mzolotukhin
Date: Wed Dec  9 12:20:28 2015
New Revision: 255133

URL: http://llvm.org/viewvc/llvm-project?rev=255133&view=rev
Log:
Revert "Revert r253253 and r253126: "Don't recompute LCSSA after loop-unrolling when possible.""

The bug in IndVarSimplify was fixed in r254976, r254977, so I'm
reapplying the original patch for avoiding redundant LCSSA recomputation.

This reverts commit ffe3b434e505e403146aff00be0c177bb6d13466.

Modified:
    llvm/trunk/lib/Transforms/Utils/LoopUnroll.cpp

Modified: llvm/trunk/lib/Transforms/Utils/LoopUnroll.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Utils/LoopUnroll.cpp?rev=255133&r1=255132&r2=255133&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Utils/LoopUnroll.cpp (original)
+++ llvm/trunk/lib/Transforms/Utils/LoopUnroll.cpp Wed Dec  9 12:20:28 2015
@@ -221,6 +221,12 @@ bool llvm::UnrollLoop(Loop *L, unsigned
 
   // Are we eliminating the loop control altogether?
   bool CompletelyUnroll = Count == TripCount;
+  SmallVector<BasicBlock *, 4> ExitBlocks;
+  L->getExitBlocks(ExitBlocks);
+  Loop *ParentL = L->getParentLoop();
+  bool AllExitsAreInsideParentLoop = !ParentL ||
+      std::all_of(ExitBlocks.begin(), ExitBlocks.end(),
+                  [&](BasicBlock *BB) { return ParentL->contains(BB); });
 
   // We assume a run-time trip count if the compiler cannot
   // figure out the loop trip count and the unroll-runtime
@@ -544,7 +550,7 @@ bool llvm::UnrollLoop(Loop *L, unsigned
     if (!OuterL && !CompletelyUnroll)
       OuterL = L;
     if (OuterL) {
-      simplifyLoop(OuterL, DT, LI, PP, SE, AC);
+      bool Simplified = simplifyLoop(OuterL, DT, LI, PP, SE, AC);
 
       // LCSSA must be performed on the outermost affected loop. The unrolled
       // loop's last loop latch is guaranteed to be in the outermost loop after
@@ -554,7 +560,11 @@ bool llvm::UnrollLoop(Loop *L, unsigned
         while (OuterL->getParentLoop() != LatchLoop)
           OuterL = OuterL->getParentLoop();
 
-      formLCSSARecursively(*OuterL, *DT, LI, SE);
+      if (CompletelyUnroll && (!AllExitsAreInsideParentLoop || Simplified))
+        formLCSSARecursively(*OuterL, *DT, LI, SE);
+      else
+        assert(OuterL->isLCSSAForm(*DT) &&
+               "Loops should be in LCSSA form after loop-unroll.");
     }
   }