https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90677
--- Comment #2 from Sergei Trofimovich <slyfox at inbox dot ru> --- (In reply to Jonathan Wakely from comment #1) > If the GCC 4.6.4 code is not valid C then it's not a bug to reject it. Can you clarify what specifically here is not valid C? Should gcc-8 also reject it? >From what I see gcc-9 has the same code in gcc/pretty-print.h as it used to be in gcc-4.6.4. I don't understand what requrements __gcc_diag__ imposes on the source to be "valid C". I can re-reduce tree-mudflap.i again to maintain the property.
