[LLVMdev] TargetLowering::isIntImmLegal(...)

[Reed Kotler]

On 03/05/2013 06:31 PM, reed kotler wrote:
> The thing I wanted for mips 16 for large literals does not seem to exist
> right now.
>
> They have MipsTargetLowering::isFPImmLegal(const APFloat &Imm, EVT VT)
>
> but not the same thing for integer literals.
>
> For Mips16, to materialize a 32 bit literal using instructions is
> expensive, both in terms of the number of registers and the number of
> instructions.
>
> You always want to just do a load of the constant from the local text
> section using a PC relative load.
>
> I could try and add this to the target independent section if there
> seems to be interest in this.
>
> I might first prototype in the Mips target area.
>
> Reed
Sorry you can materialize using instructions without a data load with 
just one register.

The main thing is that you always use at least 16 bits more by 
materializing with instructions (as opposed to a data load) and it can 
be as much as 48 bit more if the literal is repeated but even if it's 
not repeated, usually you will save 32 bits.