[ShrinkWrap] Fix FindIDom to only have one kind of failure.

FindIDom() can fail in two different ways - it can either return nullptr or the
block itself, depending on the circumstances. Some users of FindIDom() check
one error condition, while others check the other.

Change it to always return nullptr on failure.
This fixes PR26004.

Differential Revision: http://reviews.llvm.org/D15847

llvm-svn: 256955

1 files changed, 4 insertions, 6 deletions

diff --git a/llvm/lib/CodeGen/ShrinkWrap.cpp b/llvm/lib/CodeGen/ShrinkWrap.cpp
index f8aa1e2b0b9..2ff86aaa51c 100644
--- a/llvm/lib/CodeGen/ShrinkWrap.cpp
+++ b/llvm/lib/CodeGen/ShrinkWrap.cpp
@@ -263,6 +263,8 @@ MachineBasicBlock *FindIDom(MachineBasicBlock &Block, ListOfBBs BBs,
     if (!IDom)
       break;
   }
+  if (IDom == &Block)
+    return nullptr;
   return IDom;
 }
 
@@ -352,13 +354,9 @@ void ShrinkWrap::updateSaveRestorePoints(MachineBasicBlock &MBB,
       if (MLI->getLoopDepth(Save) > MLI->getLoopDepth(Restore)) {
         // Push Save outside of this loop if immediate dominator is different
         // from save block. If immediate dominator is not different, bail out.
-        MachineBasicBlock *IDom = FindIDom<>(*Save, Save->predecessors(), *MDT);
-        if (IDom != Save)
-          Save = IDom;
-        else {
-          Save = nullptr;
+        Save = FindIDom<>(*Save, Save->predecessors(), *MDT);
+        if (!Save)
           break;
-        }
       } else {
         // If the loop does not exit, there is no point in looking
         // for a post-dominator outside the loop.