[SimplifyCFG] Preserve !llvm.mem.parallel_loop_access when merging

When SimplifyCFG merges identical instructions from both sides of a diamond, it
can preserve !llvm.mem.parallel_loop_access (as it does with most of the other
metadata). There's no real data or control dependency change in this case.

llvm-svn: 267515
diff --git a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
index 23199b3..4239764 100644
--- a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -1143,7 +1143,8 @@
         LLVMContext::MD_fpmath,  LLVMContext::MD_invariant_load,
         LLVMContext::MD_nonnull, LLVMContext::MD_invariant_group,
         LLVMContext::MD_align,   LLVMContext::MD_dereferenceable,
-        LLVMContext::MD_dereferenceable_or_null};
+        LLVMContext::MD_dereferenceable_or_null,
+        LLVMContext::MD_mem_parallel_loop_access};
     combineMetadata(I1, I2, KnownIDs);
     I2->eraseFromParent();
     Changed = true;