[LLVMdev] Reading Static Values

Nick Lewycky nicholas at mxc.ca
Sat Sep 24 13:02:40 PDT 2011

On 09/24/2011 12:21 PM, bdavis at cs.fsu.edu wrote:
> Hi,
> I'm currently trying to translate LLVM IR language to VPO .dec file
> specification. I'm using LLVM source parser in the same way that it is
> used in tools llc or llvm-as. One issue I'm having is I cannot find
> any static values. For example, in a global declaration i.e. '@a =
> global i32 7, align 4' I cannot get '7' from the parsed structure.

GlobalVariable has the method getInitializer() which will return a 
Constant*. You can then dyn_cast<ConstantInt*>(...) that value to turn 
it into a ConstantInt and retrieve the concrete number from it. If it's 
not an integer, the dyn_cast will return NULL.
> Similarly (sort of), once I'm looking at a parsed Function, and I go
> into a BasicBlock, and get say and add Instruction, and I get its
> operands, I can't get static values. If for example the Instruction
> was '%add = add i32 %tmp, 60', I can get the name of value 'tmp' which
> is enough, but I can't get the value '60'.

I->getOperand(1) retrieves the second operand as a Value*. If a dyn_cast 
to ConstantInt* is successful, then it's a constant integer and you can 
read off the value with getValue().

In general, I recommend familiarizing yourself with the class 
hierarchies for Value and Type. I keep this page bookmarked: 
http://llvm.org/doxygen/hierarchy.html for these sorts of questions.


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