[LLVMdev] Inserting trace information during opt transformations

[Sarah Thompson]

Hi all,

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):

	std::ostringstream instr;
	(*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;
		args.push_back(PointerType::get(Type::Int8Ty));
		
		FunctionType *FT = FunctionType::get(Type::VoidTy, args, false);
		TraceFunc = M.getOrInsertFunction("mcp_trace_instruction", FT);

		return true;		
	}

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.
opt((anonymous namespace)::PrintStackTrace()+0x15)[0x8346cf5]
/lib/tls/libc.so.6(abort+0xe9)[0xbd3209]
/lib/tls/libc.so.6(__assert_fail+0x101)[0xbcad91]
opt[0x82ec15e]
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,
Sarah