Revert "Revert r253253 and r253126: "Don't recompute LCSSA after loop-unrolling when...

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.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@255133 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Transforms/Utils/LoopUnroll.cpp b/lib/Transforms/Utils/LoopUnroll.cpp
index ad4c388e4066aa0c69ecbe40777748f85e02abfd..44dde1b51cfcb911fe2f070e918a9856618cb99e 100644 (file)
--- a/lib/Transforms/Utils/LoopUnroll.cpp
+++ b/lib/Transforms/Utils/LoopUnroll.cpp
@@ -221,6 +221,12 @@ bool llvm::UnrollLoop(Loop *L, unsigned Count, unsigned TripCount,
 
   // 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 Count, unsigned TripCount,
     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 Count, unsigned TripCount,
         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.");
     }
   }