[PR25538]: Fix a failure caused by r253126.

In r253126 we stopped to recompute LCSSA after loop unrolling in all
cases, except the unrolling is full and at least one of the loop exits
is outside the parent loop. In other cases the transformation should not
break LCSSA, but it turned out, that we also call SimplifyLoop on the
parent loop, which might break LCSSA by itself. This fix just triggers
LCSSA recomputation in this case as well.

I'm committing it without a test case for now, but I'll try to invent
one. It's a bit tricky because in an isolated test LoopSimplify would
be scheduled before LoopUnroll, and thus will change the test and hide
the problem.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@253253 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Transforms/Utils/LoopUnroll.cpp b/lib/Transforms/Utils/LoopUnroll.cpp
index 3999989ec897a167f769a0ec8e00b240f0ab898c..44dde1b51cfcb911fe2f070e918a9856618cb99e 100644 (file)
--- a/lib/Transforms/Utils/LoopUnroll.cpp
+++ b/lib/Transforms/Utils/LoopUnroll.cpp
@@ -550,7 +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
@@ -560,7 +560,7 @@ bool llvm::UnrollLoop(Loop *L, unsigned Count, unsigned TripCount,
         while (OuterL->getParentLoop() != LatchLoop)
           OuterL = OuterL->getParentLoop();
 
-      if (CompletelyUnroll && !AllExitsAreInsideParentLoop)
+      if (CompletelyUnroll && (!AllExitsAreInsideParentLoop || Simplified))
         formLCSSARecursively(*OuterL, *DT, LI, SE);
       else
         assert(OuterL->isLCSSAForm(*DT) &&