On 20/08/2020 06:40, Senthil Kumar Selvaraj via Gcc wrote:
What I didn't understand was the (set-attr "cc<cccc><ccnz><ccnzvc>")
part - as far I can tell, this results in (set_attr "cc_enabled" ...) in
all of the three substituted patterns, so I wondered why not just have
(set_attr "cc_enabled" ...) in the original define_insn instead.
I now realize that with (set-attr "cc<cccc><ccnz><ccnzvc>"), the original
unsubstituted pattern will have only a (set_attr "cc" ...) and would
therefore not match the attr check for "enabled" - correctly so, as the
original insn pattern clobbers CRIS_CC0_REGNUM. Did I get that right?
The best (only?) way to understand define_subst is to read the expanded
machine description. This is not written anywhere, by default, but
there's a way to get it.
cd <build>/gcc
make mddump
less tmp-mddump.md
Not only are all the define_subst expanded, but so are all the other
iterators.
HTH
Andrew
