Efficient 64b operations

[Jim Wilson]

Jan Hoogerbrugge wrote:
> This works fine except that it could be better in the case
> a 32 bit value is added to a 64-bit value. Here is an example
> where "1" is added to a long long.

RTL would be more useful as an example.  The optimizer does not work on 
Trimedia instructions, it works on RTL, so it isn't obvious what is 
happening here.

We may also need info about your target port, patterns in the md file, 
macros in the .h file, etc.

> Any idea whether peepholes for this would help?

I would think peepholes should be unnecessary for something as simple as 
this, but we don't have enough info.

> Alternatively, I could test in the expansion whether I am adding
>        - two 64b registers,
>        - a 64b register and a 64b constant,
>        - a 64b register and a 32b register,
>        - or a 64b register and a 32b constant.
> Any idea on how to do this? The which_alternative variable does not
> seem to work.

You can use register_operand to check for registers, GET_CODE (x) == 
CONST_INT to check for constants, etc.  However, this doesn't help if a 
constant is put into a register before the adddi3 pattern is called, so 
this won't completely solve your problem.

which_alternative only works after reload, and only if you have multiple 
constraints alternatives.  It is mainly useful for emitting assembly 
language after optimization.

> Are there architectures where I could learn from?

Probably, try looking at some of them.
-- 
Jim Wilson, GNU Tools Support, http://www.SpecifixInc.com