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Re: Proposed major change to combine
- To: amylaar at cambridge dot redhat dot com
- Subject: Re: Proposed major change to combine
- From: kenner at vlsi1 dot ultra dot nyu dot edu (Richard Kenner)
- Date: Sat, 10 Mar 01 06:10:06 EST
- Cc: gcc at gcc dot gnu dot org
combine chokes on anything involving more than three insns.
True.
Moreover, a lot of optimizations try to recognize insn, rather than go
through the expanders.
That's true too.
I agree this is a tradeoff and there are *sometimes* cases where it's valuable
to have an insn that corresponds to multiple instructions (a good example
is movdi on 32-bit machines), but I'd be against adding code to combine to
"understand" these cases since I think they are rare and are to be avoided
as much as possible (as I said, they also mess up heuristics in loop.c0.