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Re: [rfc] multi-word subreg lowering pass

On Sat, May 07, 2005 at 10:04:12AM -0400, Paul Schlie wrote:
> - For a byte word size target like AVR for which UNITS_PER_WORD == 1,
>   would all operations be decomposed to QI mode operations?


> - What effect if any would it's presently necessary lie about it's
>   word size (i.e. lies within libgcc2 and claims UNITS_PER_WORD == 4
>   in order to trick it into selecting reasonably correct operand modes)
>   have on the generated code for functions defined within libgcc2?

No idea.

> - Out of curiosity, why not leave all decomposed operations in their
>   subreg form, thereby maintaining the logical integrity of their operand
>   modes? i.e. the above decomposes to something like:
>      (set (subreg:SI 100 0) (and:SI (reg:SI x) (subreg:SI y 0)))
>      (set (subreg:SI 100 1) (and:SI (const_int 0) (subreg:SI y 1)))
>   which seems both simpler, and does not require introduction of new
>   semantics which complicate multi-word/sub-reg input operand expressions.

The Object is to present the register allocator with something that
it has more freedom to work with.  This doesn't achieve that goal.


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