On 6/3/2021 2:00 AM, Segher Boessenkool wrote:
Hi!
On Thu, Jun 03, 2021 at 01:22:38PM +0800, Kewen.Lin wrote:
on 2021/6/3 上午7:52, Segher Boessenkool wrote:
- add a new "define_independent_insn_and_split" that has the
current semantics of define_insn_and_split. This should be
mechanical.
I'd rather not have that -- we can just write separate define_insn and
define_split in that case.
Not sure if someone would argue that he/she would like to go with one shared
pattern as before, to avoid any possible differences between two seperated
patterns and have good maintainability (like only editing on place) and
slightly better efficiency.
You only would do this if you have a different insn condition and split
condition, which is a very important thing to know, it doesn't hurt to
draw attention to it. The efficiency is exactly the same btw,
define_insn_and_split is just syntactic sugar.
The whole point of requiring the split condition to start with && is so
it will become harder to mess things up (it will make the gen* code a
tiny little bit simpler as well). And there is no transition period or
anything like that needed either. Just the bunch that will break will
need fixing. So let's find out how many of those there are :-)
Exactly. While these empty conditions or those not starting with "&&"
are technically valid, they're all suspicious from a port correctness
standpoint, particularly if the main condition is non-empty.
Having made that mistake when converting the H8 away from CC0, I can say
fairly confidently that if we had this in place a year ago that those
mistakes would likely have been avoided. Thankfully the H8 isn't a
heavily used port and has limped along until I stumbled over the issue a
week or so ago while polishing some improvements to the port.
Jeff
