[RFC] Feedback on approach for adding support for V8QI->V8HI widening patterns

[Joel Hutton]

Hi Richard(s),

I'm just looking to see if I'm going about this the right way, based on the discussion we had on IRC. I've managed to hack something together, I've attached a (very) WIP patch which gives the correct codegen for the testcase in question (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98772). It would obviously need to support other widening patterns and differentiate between big/little endian among other things.

I added a backend pattern because I wasn't quite clear which changes to make in order to allow the existing backend patterns to be used with a V8QI, or how to represent V16QI where we don't care about the top/bottom 8. I made some attempt in optabs.c, which is in the patch commented out, but I'm not sure if I'm going about this the right way.

Joel
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