PIShellcode is a Position-Independent shellcode loader. It's basically a C Program compiled as a PIC. It's a modified version of Mr mattifestation's PIC_BindShell project. Here are the details on how to write optimized shellcode for Windwos in C and Visual Studio which he greatly explains. http://www.exploit-monday.com/2013/08/writing-optimized-windows-shellcode-in-c.html

The program currently uses a static XOR key 0x32 0x47 0x68 0x84 0x59 0x91 0x34 0x17 0x58 0x13 0x77 0x69 0x09 0x11 0x19 0x94 and static shellcode file from location C:\Users\Public\code.dat. Both can be changed in the code. Only 64 bit architecture is supported.

For whatever reason compiling & linking the code in Visual Studio 2017 with fully optimized arguments /O1, The generated code ends up having data segment register offsets to .rdata section in it. So in order to actualy obtain position independent code, Maximum optimization feature in compiler settings is turned off.

Look-into: merging two sections into one.