[LLVMdev] Is addrspacecast implemented on Windows?

Kai Nacke kai.nacke at redstar.de
Mon Jan 27 12:04:09 PST 2014

Hi all!

On x86_64, segment prefix fs: is in address space 257 and gs: in address 
space 256. (BTW: are there constants for these magic values?) How can I 
use this in IR? I want to express this assembler code in IR:

                  mov RAX, 8;
                  mov RAX, GS:[RAX];

I tried the following:

define i64 @getStackBottom(i64 %addr) {
   %ptr = inttoptr i64 %addr to i64*
   %fs_ptr = addrspacecast i64* %ptr to i64 addrspace(256)*
   %bottom = load i64 addrspace(256)* %fs_ptr, align 1
   ret i64 %bottom

but this results in

LLVM ERROR: Cannot select: 0xcc6c60: i64 = addrspacecast 0xcc6b60[0 -> 
256] [ORD=3] [ID=6]
   0xcc6b60: i64,ch = CopyFromReg 0xc95e38, 0xcc6a60 [ORD=1] [ID=5]
     0xcc6a60: i64 = Register %vreg0 [ID=1]
In function: getStackBottom
Stack dump:
0.      Program arguments: llc thr_ll.ll
1.      Running pass 'Function Pass Manager' on module 'thr_ll.ll'.
2.      Running pass 'X86 DAG->DAG Instruction Selection' on function 

Do I miss something here? Or is this simply not yet implemented?


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