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llvmllvm-irllvm-c++-api

LLVM get operand and lvalue name of an instruction

For a LLVM IR instruction like %cmp7 = icmp eq i32 %6 %7 I want to get all three register/symbol names (i.e. %cmp %6 and %7)

Now I can get string %cmp by command pi->getName() where pi is Instruction pointer. But when I try to get oprand names I got empty string by typing pi->getOperand(0)->getName().

I tried isa<Instruction>(pi->getOperand(0)) to check whether this is an instruction and it returned true but pi->getOperand(0)->hasName() returned false. Things make me feeling strange is that why both pi and pi->getOperand(0) are instructions but only pi has name?

Is there any thoughts I can get operand name (string %6 and %7 here)by using API?

LLVM version I'm using is 3.4.2

Solution

  • Names are optional for LLVM instructions, and indeed the two operands of your icmp instruction in this case don't have a name, hence the empty string.

    When you print an LLVM module to an .ll file then the writer allocates a %<num> name for each instruction to make it human-readable, but this is only something the writer does during printing, that string does not exist in the actual module.