[LLVMdev] Advice on MachineMoves and SEH

[Villmow, Micah]

> -----Original Message-----
> From: llvmdev-bounces at cs.uiuc.edu [mailto:llvmdev-bounces at cs.uiuc.edu]
> On Behalf Of Jim Grosbach
> Sent: Thursday, June 02, 2011 9:11 AM
> To: Rafael Ávila de Espíndola
> Cc: llvmdev at cs.uiuc.edu
> Subject: Re: [LLVMdev] Advice on MachineMoves and SEH
> 
> 
> On Jun 2, 2011, at 6:20 AM, Rafael Ávila de Espíndola wrote:
> 
> > On 11-06-02 6:56 AM, Anton Korobeynikov wrote:
> >> Hi Chip,
> >>
> >>> Because of all this, it's hard to reconstruct the SEH information
> from
> >>> the MachineMove array. I have thought about adding a new array
> specific
> >>> to SEH information, but I'm not sure how you guys would feel about
> that.
> >>> Any ideas on how to solve this problem?
> >> Same problem with ARM-specific EH. I ended with own information
> >> scheme, where instructions are marked as "frame related" during all
> >> prologue&  epilogue emission and later are "recognized" during the
> MI
> >> =>  MCInst lowering. You might want to look into ARM backend, maybe
> we
> >> can somehow "generalize" this approach.
> >>
> >
> > Yes, the current model of producing a on the side vector of machine
> > moves doesn't look like the best thing to do now that we produce cfi
> > directives.
> >
> > I was thinking about just creating pseudo instructions that map 1:1
> to
> > the cfi directives (and ARM, and SEH). Codegen would create the
> > appropriate one depending on the target. This would also avoid the
> silly
> > labels that we still create when producing cfi.
> >
> 
> Pseudo instructions are problematic. That means every function pass
> that iterates over the instructions has to explicitly check for them to
> make sure they don't affect optimization. We already have to do that
> for debug_value instructions, and it's really unpleasant and error
> prone.
[Villmow, Micah] What about adding a field to the Instruction class that specifies if it is a pseudo instruction or not. That way it is the same check no matter how many pseudo-instructions are added. While this might not be the best solution, if it is something that has to be done for debug_value instructions already, and no better solution is proposed, it might be helpful.
> 
> -Jim
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