On Fri, 14 Aug 2020, Senthil Kumar Selvaraj via Gcc wrote: > As you can deduce from the (set_attr "cc" ..), only constraint > alternatives 0,2,3 and 6 clobber CC - others leave it unchanged.
Yes, I recognize that. > My first version of the port adds a post-reload splitter that adds a > (clobber (reg:CC REG_CC)) unconditionally, and it appears to work. Ouch, temporarily lying to gcc here. > If I > do want to add the clobber conditionally, would something like the below > be a good way to do it (get_cc_reg_clobber_rtx returns either const0_rtx > or cc_reg_rtx based on get_attr_cc (insn))? Or is there a better/cleaner way? I suggest having a look at what I did for the CRIS port. Check the git history. In short: - Add the clobber initially, to *all* patterns. - Add postreload splitters for the special combinations that don't clobber CC (ones without clobbering CC). - Use the old "cc" attribute to control and generate clobber/useful CC-setting alternatives (for various new CC_ modes) with use of define_subst. No regressions in CC quality (with one pending patch). brgds, H-P
