SimplifyCFG: don't turn volatile stores to null/undef into unreachable. Fixes PR7369.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@105914 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Transforms/Scalar/SimplifyCFGPass.cpp

@@ -137,6 +137,9 @@ static bool MarkAliveBlocks(BasicBlock *BB,
       // they should be changed to unreachable by passes that can't modify the
       // CFG.
       if (StoreInst *SI = dyn_cast<StoreInst>(BBI)) {
+        // Don't touch volatile stores.
+        if (SI->isVolatile()) continue;
+
         Value *Ptr = SI->getOperand(1);
         
         if (isa<UndefValue>(Ptr) ||