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

Reed Kotler rkotler at mips.com
Tue Mar 5 18:51:41 PST 2013

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.

More information about the llvm-dev mailing list