In several of the transformations I'm working on I need to embed the logical equivalent of puts/printf/etc. calls inline with code. I am having some difficulties getting the transformation code right. As I understand it, I should be creating a ConstantArray based on the string (in this case I'm taking an instruction, 'disassembling' it to an ostringstream then turning it into a constant array):
(*wp)->print(instr); Constant *itext = ConstantArray::get(instr.str());
This bit seems OK. I am calling a function in my run time system with the signature
void mcp_trace_instruction(const char *)
by first declaring it inside doInitialization():
virtual bool doInitialization(Module &M)
std::vector<const Type*> args;
FunctionType *FT = FunctionType::get(Type::VoidTy, args, false);
TraceFunc = M.getOrInsertFunction("mcp_trace_instruction", FT);
then inserting a suitable CallInst instruction
new CallInst(TraceFunc, gepinst, "", *wp);
Looking at disassembly output from similar code, I can't just pass the constant array directly to the call because I need a GetElementPtrInst conversion. This is the thing I'm having trouble with. My current attempt is:
GetElementPtrInst *gepinst = new GetElementPtrInst(itext, ConstantInt::get(Type::Int32Ty, 0), ConstantInt::get(Type::Int32Ty, 0), "", *wp);
but it fails as follows:
opt -load ~/llvm-tools/mcp-build/Debug/lib/MCPTransforms.so -trace-instructions -lowerselect -lowerallocs -lowergc -lowerinvoke -lowerswitch -reg2mem -insertyieldpoints -trace-memory -o Abort.fbc Abort.bc
opt: /usr/local/rse/llvm/src/lib/VMCore/Instructions.cpp:872: const llvm::Type* checkType(const llvm::Type*): Assertion `Ty && "Invalid GetElementPtrInst indices for type!"' failed.
make: *** [Abort.fbc] Aborted
The pass that is blowing up is -trace-instructions, which is intended basically just to go through the module inserting mcp_trace_instruction calls before each instruction, before any other modifications are made to the code (I have to trace instructions this way because by the time the other transformations run, I end up with something not very much like the original code).
I've tried a few other obvious-looking alternatives, but I seem to be stabbing in the dark. If anyone could suggest the correct GetElementPtrInst configuration I would be very grateful -- I've already wasted a couple of days on this.
Thank you in advance,