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

This fixes PR30454.

llvm-svn: 287379
diff --git a/llvm/lib/Transforms/Utils/LoopSimplify.cpp b/llvm/lib/Transforms/Utils/LoopSimplify.cpp
index d24c1c4..00cda2a 100644
--- a/llvm/lib/Transforms/Utils/LoopSimplify.cpp
+++ b/llvm/lib/Transforms/Utils/LoopSimplify.cpp
@@ -530,7 +530,7 @@
 
       // 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;
     }
   }