[LLVMdev] Memory Altering/Accessing Instructions

[Prakash Prabhu]

Hi John,

Thanks for the reply. I am planning to use this information as a part
of Analysis, so I guess it should be ok since it is before code
generation.

- Prakash

On Wed, Sep 24, 2008 at 4:57 PM, John Criswell <criswell at cs.uiuc.edu> wrote:
> Prakash Prabhu wrote:
>> Hi all,
>>
>> Would it be correct to say that the only instructions in LLVM IR that
>> modify/access memory potentially are the following:
>>
> I believe that every instruction has a
> mayWriteToMemory()/mayReadToMemory() method that you can use to
> determine this information.  See
> http://llvm.org/doxygen/classllvm_1_1Instruction.html (the LLVM doxygen
> info on llvm::Instruction) for more details.  I believe these methods
> describe whether memory is read/written in a way visible from the LLVM
> IR; I don't believe they'll take into account things like read/writes
> due to register spills created by the code generator.
>
>> (1) LoadInst : Ref
>> (2) StoreInst : Mod
>> (3) VAArgInst : Ref (?)
>> (4) AllocaInst : Mod
>> (5) MallocInst : Mod
>> (6) FreeInst : Mod
>> (7) CallInst : Mod/Ref ?
>>
>> Also, my earlier impression was that the GEP instruction only computes
>> the effective address and does not modify/access any memory location.
>> Is that true ?
>>
> This is correct.
>
>> If I have missed other instructions that could alter/modify memory,
>> please let me know.
>>
>> Thanks for your time.
>>
> -- John T.
>> - Prakash
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