[LLVMdev] modify instructions

Vikram S. Adve vadve at cs.uiuc.edu
Thu Sep 26 10:51:01 PDT 2002

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).


> -----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
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