sparse-llvm functions must be cast to correct type before calling

sparse-llvm functions must be cast to correct type before calling

[Dibyendu Majumdar]

Hi,

The following test (adapted from snippet posted by Linus) fails in sparse-llvm:

typedef unsigned int (*binop_t)(int, int);
typedef unsigned int (*unop_t)(int);
extern int printf(const char *, ...);
#define BINOP 0
#define UNOP 1
static unsigned int execute(int type, void *fn, int arg1, int arg2)
{
 if (type == BINOP)
  return ((binop_t)fn)(arg1,arg2);
 return ((unop_t)fn)(arg1);
}
static unsigned int unary(int arg1)
{
 return arg1+3;
}
int main(void)
{
 return execute(UNOP, unary, 3, 10) == 6 ? 0 : 1;
}

To resolve this before calling a function we need to cast it to the
expected type. This can be done like this in output_op_call():

 struct symbol *ftype = get_function_basetype(insn->fntype);

...

 LLVMTypeRef function_type = symbol_type(C, fn->module, ftype);
 LLVMTypeRef fptr_type = LLVMPointerType(function_type, 0);
 LLVMTypeRef bytep = LLVMPointerType(LLVMInt8Type(), 0);
 target = LLVMBuildBitCast(fn->builder, func, bytep, name);
 target = LLVMBuildBitCast(fn->builder, target, fptr_type, name);
 target = LLVMBuildCall(fn->builder, target, args, n_arg, name);
 insn->target->priv = target;


Thanks and Regards
Dibyendu

Re: sparse-llvm functions must be cast to correct type before calling

[Luc Van Oostenryck]

On Thu, Mar 16, 2017 at 08:58:25PM +0000, Dibyendu Majumdar wrote:
> Hi,
> 
> The following test (adapted from snippet posted by Linus) fails in sparse-llvm:

...
 
> To resolve this before calling a function we need to cast it to the
> expected type. This can be done like this in output_op_call():

This is a very general problem with sparse-llvm, directly caused
by the fact the sparse associates type to instructions and LLVM
to the values.

What's happening is that the first time a pseudo is used
it's a value is created (with the curret type, of course)
*and* is stored in the pseudo::priv.
The next times this pseudo is used the LLVM value is directly
taken from the ::priv without regards for the current type.

In the coming update of the LLVM serie, I added an helper
for this sort of things: adjust_type(). But it need to be
added at the right place(s).

-- Luc