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Re: [PATCH: PR target/44999] Replace "and r0, r0, #255" with uxtb in thumb2


On 07/26/2010 11:08 AM, Carrot Wei wrote:
I'm not an expert of combine, and I find the following comments in combine.c:

    We try to combine each pair of insns joined by a logical link.
    We also try to combine triples of insns A, B and C when
    C has a link back to B and B has a link back to A.

Only one insn is involved in the change, so combine should not check it.

Right, of course. I check the i386 backend and it is also doing the same optimization as your patch does, i.e. without the help of the middle-end.


(It actually does it using a constraint instead of RTL, but that doesn't really matter and would be a bit harder to do for ARM).

Paolo


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