[LoopSimplify] Preserve LCSSA when removing edges from unreachable blocks.

This fixes PR30454.

llvm-svn: 287379

2 files changed, 4 insertions, 3 deletions

diff --git a/llvm/lib/Transforms/Utils/Local.cpp b/llvm/lib/Transforms/Utils/Local.cpp
index 3ad5f58e6cb..01a5579e1ed 100644
--- a/llvm/lib/Transforms/Utils/Local.cpp
+++ b/llvm/lib/Transforms/Utils/Local.cpp
@@ -1369,12 +1369,13 @@ unsigned llvm::removeAllNonTerminatorAndEHPadInstructions(BasicBlock *BB) {
   return NumDeadInst;
 }
 
-unsigned llvm::changeToUnreachable(Instruction *I, bool UseLLVMTrap) {
+unsigned llvm::changeToUnreachable(Instruction *I, bool UseLLVMTrap,
+                                   bool PreserveLCSSA) {
   BasicBlock *BB = I->getParent();
   // Loop over all of the successors, removing BB's entry from any PHI
   // nodes.
   for (BasicBlock *Successor : successors(BB))
-    Successor->removePredecessor(BB);
+    Successor->removePredecessor(BB, PreserveLCSSA);
 
   // Insert a call to llvm.trap right before this.  This turns the undefined
   // behavior into a hard fail instead of falling through into random code.
diff --git a/llvm/lib/Transforms/Utils/LoopSimplify.cpp b/llvm/lib/Transforms/Utils/LoopSimplify.cpp
index d24c1c41557..00cda2af00c 100644
--- a/llvm/lib/Transforms/Utils/LoopSimplify.cpp
+++ b/llvm/lib/Transforms/Utils/LoopSimplify.cpp
@@ -530,7 +530,7 @@ ReprocessLoop:
 
       // Zap the dead pred's terminator and replace it with unreachable.
       TerminatorInst *TI = P->getTerminator();
-      changeToUnreachable(TI, /*UseLLVMTrap=*/false);
+      changeToUnreachable(TI, /*UseLLVMTrap=*/false, PreserveLCSSA);
       Changed = true;
     }
   }