[LLVMdev] [PATCH] RegScavenger::scavengeRegister

[Hal Finkel]

----- Original Message -----
> From: "Jakob Stoklund Olesen" <stoklund at 2pi.dk>
> To: "Akira Hatanaka" <ahatanak at gmail.com>
> Cc: "LLVM Developers Mailing List" <llvmdev at cs.uiuc.edu>, "Hal Finkel" <hfinkel at anl.gov>
> Sent: Monday, March 25, 2013 3:06:16 PM
> Subject: Re: [LLVMdev] [PATCH] RegScavenger::scavengeRegister
> 
> 
> 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?

In part, yes. It is for eliminating FIs and expanding some pseudos for spilling registers that don't have direct load/store instructions.

 -Hal

> 
> /jakob
> 
>