Re: GCC-How does the coding style affect the insv pattern recognization?

[fanqifei <fanqifei at gmail dot com>]

2010/1/18 Adam Nemet <adambnemet@gmail.com>:
> fanqifei <fanqifei@gmail.com> writes:
>> ? ? Paolo Bonzini said that insv instruction might be synthesized
>> later by combine. But combine only works on at most 3 instructions and
>> insv is not generated in such case.
>> ? ? So exactly when will the insv pattern be recognized and how does
>> the coding style affect it?
>
> Sorry for jumping in late. ?See make_file_assigment in combine.c.
>
> The problem usually is that:
>
> ?(set A (ior (and B C1) OTHER))
>
> can only be turned into a bit-insertion if A and B happen to be the same
> pseudos.
>
> Adam
>
I did found such kind of pattern for some simple C statements in rtl dump.
Unfortunately, A and B are not same.
Is it possible and easy to move B to A firstly and replace B with A in the insn?
Anyway, this is not required if it's impracticable.

Qifei Fan