Fix SplitBlockPredecessors' LoopInfo updating code to handle the case

where a loop's header is being split and it has predecessors which are not
contained by the most-nested loop which contains the loop.
This fixes PR5235.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@84505 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 40 insertions, 8 deletions

diff --git a/lib/Transforms/Utils/BasicBlockUtils.cpp b/lib/Transforms/Utils/BasicBlockUtils.cpp
index 4931ab3..35907fd 100644
--- a/lib/Transforms/Utils/BasicBlockUtils.cpp
+++ b/lib/Transforms/Utils/BasicBlockUtils.cpp
@@ -425,14 +425,26 @@ BasicBlock *llvm::SplitBlockPredecessors(BasicBlock *BB,
 
   if (L) {
     if (IsLoopEntry) {
-      if (Loop *PredLoop = LI->getLoopFor(Preds[0])) {
-        // Add the new block to the nearest enclosing loop (and not an
-        // adjacent loop).
-        while (PredLoop && !PredLoop->contains(BB))
-          PredLoop = PredLoop->getParentLoop();
-        if (PredLoop)
-          PredLoop->addBasicBlockToLoop(NewBB, LI->getBase());
-      }
+      // Add the new block to the nearest enclosing loop (and not an
+      // adjacent loop). To find this, examine each of the predecessors and
+      // determine which loops enclose them, and select the most-nested loop
+      // which contains the loop containing the block being split.
+      Loop *InnermostPredLoop = 0;
+      for (unsigned i = 0; i != NumPreds; ++i)
+        if (Loop *PredLoop = LI->getLoopFor(Preds[i])) {
+          // Seek a loop which actually contains the block being split (to
+          // avoid adjacent loops).
+          while (PredLoop && !PredLoop->contains(BB))
+            PredLoop = PredLoop->getParentLoop();
+          // Select the most-nested of these loops which contains the block.
+          if (PredLoop &&
+              PredLoop->contains(BB) &&
+              (!InnermostPredLoop ||
+               InnermostPredLoop->getLoopDepth() < PredLoop->getLoopDepth()))
+            InnermostPredLoop = PredLoop;
+        }
+      if (InnermostPredLoop)
+        InnermostPredLoop->addBasicBlockToLoop(NewBB, LI->getBase());
     } else {
       L->addBasicBlockToLoop(NewBB, LI->getBase());
       if (SplitMakesNewLoopHeader)
diff --git a/test/Transforms/LoopSimplify/unreachable-loop-pred.ll b/test/Transforms/LoopSimplify/unreachable-loop-pred.ll
new file mode 100644
index 0000000..faaaf97
--- /dev/null
+++ b/test/Transforms/LoopSimplify/unreachable-loop-pred.ll
@@ -0,0 +1,20 @@
+; RUN: opt -S -loopsimplify -disable-output -verify-loop-info -verify-dom-info < %s
+; PR5235
+
+; When loopsimplify inserts a preheader for this loop, it should add the new
+; block to the enclosing loop and not get confused by the unreachable
+; bogus loop entry.
+
+define void @is_extract_cab() nounwind {
+entry:
+  br label %header
+
+header:                                       ; preds = %if.end206, %cond.end66, %if.end23
+  br label %while.body115
+
+while.body115:                                    ; preds = %9, %if.end192, %if.end101
+  br i1 undef, label %header, label %while.body115
+
+foo:
+  br label %while.body115
+}