[LLVMdev] [PATCH] RegScavenger::scavengeRegister

[Jakob Stoklund Olesen]

On Mar 25, 2013, at 12:04 PM, Akira Hatanaka <ahatanak at gmail.com> wrote:

> This patch adds parameter "EliminateFI" to RegScavenger::scavengeRegister, which tells register scavenger not to eliminate frame index of the emergency spill slot if set to false.
> 
> I have pseudo load, store and copy instructions which are generated during register allocation and expanded post-RA but before the final stack size is known. I use register scavenger to search for a temporary integer GPR that is used during pseudo-expansion.
> 
> This is what happens during pseudo-expansion:
> 
> The following pseudo
> 
> LoadAC $acc, FI // Pseudo load instructions. Load from FI to accumulator $acc.
> 
> 
> is expanded into this sequence:
> 
> LW $reg, FI         // load from FI to temporary GPR $reg
> MTLO $reg         // copy $reg to register LO
> LW $reg, FI + 4   // load from FI+4 to GPR $reg
> MTHI $reg          // copy $reg to register HI

Hi Akira,

The register scavenger is not really supposed to be used in more than one pass, because you would need to allocate a separate emergency spill slot for each pass.

I think Hal is trying to solve a very similar problem for PPC.

Hal, are you expanding pseudos during PEI?

/jakob