Enable integrated assembler for MIPS64 targets except N32 ABI explicitly selected by the -mabi=n32 command line option or mips64(el)-linux-gnuabin32 target triple.
Good point. In fact, integrated assembler for GNUABIN32 was enabled in the MipsMCAsmInfo ctor by me and by mistake. I have another patch which fix it. But anyway there is a problem - we cannot check command line options in the MipsMCAsmInfo. So I'm going to test current MIPS N32 ABI implementation. Maybe we are ready to enable integrated assembler for it. In that case both Generic_GCC::IsIntegratedAssemblerDefault() and MipsMCAsmInfo ctor can be simplified.
IMHO it would be best to try and deal with as many known / exposed issues with the N32 support and then just enable IAS across the board. Then tackle any remaining issues as they come up.