Hi,
I'm trying to get my head around c++ - IR - c++ API and getting used
tramform manual information to code.
The manual states alloca is defined for <type>. FunstionType is a type, so
alloca for functionType should be possible? Not?
If we have a valid Module *m
we can get an allocate instruction allocating space for a non-argumented
function as follows:
AllocaInst* pa2 = new AllocaInst( FunctionType::get(
Type::getVoidTy(m->getContext()), false )
, 1, "myName");
but how about nonvar-argumented functions? E.g. I32,I16
std::vector<Type*>FuncTy_args;
FuncTy_args.push_back(IntegerType::get(mod->getContext(), 32));
FuncTy_args.push_back(IntegerType::get(mod->getContext(), 16));
AllocaInst* pa3 = new AllocaInst( FunctionType::get(
Type::getVoidTy(m->getContext()), FuncTy_args ,false )
, 1, "MyName");
does this make sense?
I guess this might not be correct, because we explicitely introduce
FuncTy_args, where we only would like to know the 'necessary memory
footprint' of it, for alloca to be able to allocate it, not?
Alex
> On Jan 15, 2015, at 3:05 AM, Alexander Poddey <alexander.poddey at gmx.net> wrote: > > Hi, > I'm trying to get my head around c++ - IR - c++ API and getting used > tramform manual information to code. > > > The manual states alloca is defined for <type>. FunstionType is a type, so > alloca for functionType should be possible? Not?I may not understand what you try to achieve because it does not make much sense to me :) As far as I understand, an alloca instruction allocate space for a variable. It does not really make sense for it to be used with a function type (do you want to store a pointer to a function of this type?). Maybe this would help: http://llvm.org/docs/tutorial/LangImpl7.html (and in any case you can check how clang is using alloca to emit llvm IR) OTH Mehdi> > > If we have a valid Module *m > > we can get an allocate instruction allocating space for a non-argumented > function as follows: > > AllocaInst* pa2 = new AllocaInst( FunctionType::get( > Type::getVoidTy(m->getContext()), false ) > , 1, "myName"); > > > but how about nonvar-argumented functions? E.g. I32,I16 > > std::vector<Type*>FuncTy_args; > FuncTy_args.push_back(IntegerType::get(mod->getContext(), 32)); > FuncTy_args.push_back(IntegerType::get(mod->getContext(), 16)); > > > AllocaInst* pa3 = new AllocaInst( FunctionType::get( > Type::getVoidTy(m->getContext()), FuncTy_args ,false ) > , 1, "MyName"); > > > does this make sense? > I guess this might not be correct, because we explicitely introduce > FuncTy_args, where we only would like to know the 'necessary memory > footprint' of it, for alloca to be able to allocate it, not? > > Alex > > > > _______________________________________________ > LLVM Developers mailing list > LLVMdev at cs.uiuc.edu http://llvm.cs.uiuc.edu > http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
> As far as I understand, an alloca instruction allocate space for a > variable. It does not really make sense for it to be used with a function > type (do you want to store a pointer to a function of this type?).Yes. if I undertand correctly, alloca allocates space for a variable. I could then want to allocate space for a function pointer. I can now see code similar to my example by using c function pointers and emitting c++API code: When translating c++ code using function pointers, the emitted llvm for int (*foo2)(double,float); looks like %foo2 = alloca i32 (double, float)*, align 8 and the c++ API code (generated by llc -march=cpp) std::vector<Type*>FuncTy_49_args; FuncTy_49_args.push_back(Type::getDoubleTy(mod->getContext())); FuncTy_49_args.push_back(Type::getFloatTy(mod->getContext())); FunctionType* FuncTy_49 = FunctionType::get( /*Result=*/IntegerType::get(mod->getContext(), 32), /*Params=*/FuncTy_49_args, /*isVarArg=*/false); PointerType* PointerTy_48 = PointerType::get(FuncTy_49, 0); AllocaInst* ptr_foo2 = new AllocaInst(PointerTy_48, "foo2", label_entry_71); This is what I had in my 1st post. So this seems to be the way to do it. This vice versa transformation between source, IR and API is quite cool! Alex