clang-format can get confused by string literals in TableGen: it knows that strings can be broken up, but doesn't seem to understand how that can be indented across line breaks, and arranges them in a weird triangular pattern. Take this output example from clang-format tools/llvm-objcopy/ObjcopyOpts.td (which has now been formatted in rL345896 with this patch applied):
defm keep_global_symbols : Eq< "keep-global-symbols", "Reads a list of symbols from <filename> and " "runs as if " "--keep-global-symbol=<symbol> " "is set for each one. " "<filename> " "contains one " "symbol per line " "and may contain " "comments " "beginning " "with" " '#'" ". " "Lead" "ing "