LowerSwitch: Fix producing invalid IR on unreachable code

If a switch was in an unreachable block that branched
to a block with a phi, it would leave phis with missing
predecessors.

llvm-svn: 301064

1 files changed, 8 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/Utils/LowerSwitch.cpp b/llvm/lib/Transforms/Utils/LowerSwitch.cpp
index b375d51005d..8959e77438e 100644
--- a/llvm/lib/Transforms/Utils/LowerSwitch.cpp
+++ b/llvm/lib/Transforms/Utils/LowerSwitch.cpp
@@ -403,6 +403,14 @@ void LowerSwitch::processSwitchInst(SwitchInst *SI,
   Value *Val = SI->getCondition();  // The value we are switching on...
   BasicBlock* Default = SI->getDefaultDest();
 
+  // Don't handle unreachable blocks. If there are successors with phis, this
+  // would leave them behind with missing predecessors.
+  if ((CurBlock != &F->getEntryBlock() && pred_empty(CurBlock)) ||
+      CurBlock->getSinglePredecessor() == CurBlock) {
+    DeleteList.insert(CurBlock);
+    return;
+  }
+
   // If there is only the default destination, just branch.
   if (!SI->getNumCases()) {
     BranchInst::Create(Default, CurBlock);