sparse-llvm subtraction of one pointer from another should result in int difference

[Dibyendu Majumdar <mobile@xxxxxxxxxxxxxxx>]

Hi,

I was investigating an error reported while compiling minilua (please
see my earlier post on minlua) and I found that one of the issues was
that the result of subtracting one pointer from another is not handled
correctly in sparse-llvm. I think the OP_SUB implementation should be
changed as follows:

 case OP_SUB:
  if (symbol_is_fp_type(C, insn->type))
   target = LLVMBuildFSub(fn->builder, lhs, rhs, target_name);
  else if (LLVMGetTypeKind(LLVMTypeOf(lhs)) == LLVMPointerTypeKind &&
   LLVMGetTypeKind(LLVMTypeOf(rhs)) == LLVMPointerTypeKind) {
   // Both arguments are pointer
   // Result will be integer
   lhs = LLVMBuildPtrToInt(fn->builder, lhs,
LLVMIntType(C->target->bits_in_pointer), "");
   rhs = LLVMBuildPtrToInt(fn->builder, rhs,
LLVMIntType(C->target->bits_in_pointer), "");
   target = LLVMBuildSub(fn->builder, lhs, rhs, target_name);
  }
  else
   target = LLVMBuildSub(fn->builder, lhs, rhs, target_name);
  break;

Thanks and Regards
Dibyendu
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