[LLVMdev] modify instructions

[Chris Lattner]

> I think since we use the replaceAllUsesWith to replace all
> uses of old one, the old one should already be a instruction
> with # of uses equals 0. So it should be Ok to directly delete
> it. Can you let me know if there is anything wrong with simple
> deletion? Why can we create illegal LLVM?

You can't 'delete' it because the instruction is probably still embedded
in the program, so data structures are still using it.

Please see this section of the programmers manual to see how to do it:
http://llvm.cs.uiuc.edu/docs/ProgrammersManual.html#schanges_deleting

And yes, after calling replaceAllUsesWith, it is legal to remove the
instruction from the program.

-Chris


> ---- Original message ----
> >Date: Thu, 26 Sep 2002 10:50:00 -0500
> >From: "Vikram S. Adve" <vadve at cs.uiuc.edu>
> >Subject: RE: [LLVMdev] modify instructions
> >To: <xli3 at uiuc.edu>, <llvmdev at cs.uiuc.edu>
> >
> >The simplest way is to create a new instruction and use
> replaceAllUsesWith
> >on the old one.
> >
> >Think about a simple way to get rid of the old one (without
> producing
> >illegal LLVM as the output of your phase).
> >
> >--Vikram
> >
> >
> >> -----Original Message-----
> >> From: llvmdev-admin at cs.uiuc.edu
> [mailto:llvmdev-admin at cs.uiuc.edu]On
> >> Behalf Of xli3 at uiuc.edu
> >> Sent: Thursday, September 26, 2002 9:24 AM
> >> To: llvmdev at cs.uiuc.edu
> >> Subject: [LLVMdev] modify instructions
> >>
> >>
> >> Hi, I have a question about the modify of instruction:
> >> Say I want to modify
> >> %a = getelementptr %struct %S, long 0, ubyte 1
> >> into
> >> %a.f0 = getelementptr int* %S.f0, long 0
> >>
> >> There are 3 ways I can think of to implement, but I'm not
> sure
> >> what should I do.
> >>
> >> 1. I can use new GetElementPtr to create a new instruction
> and
> >> use ReplaceInstWithInst() function to replace the old one.
> >>
> >> 2. I can use new GetElementPtr to create a new instruction
> and
> >> then insert it into the code, then delete the old
> instruction,
> >> but the problem is the program will automatically change
> the
> >> name of the new instruction if you give it the same name
> with
> >> the old one?
> >>
> >> 3. Just modify the operand 0 and delete the operand 2. But
> I
> >> didn't see an command to delete an operand.
> >>
> >> Please let me know in LLVM, what's the best way to handle
> >> this? Thanks,
> >>
> >> xiaodong
> >> _______________________________________________
> >> LLVM Developers mailing list
> >> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> >> http://mail.cs.uiuc.edu/mailman/listinfo/llvmdev
> >>
> >
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-Chris

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