[llvm-dev] llvm.experimental.gc.statepoint genarates wrong Stack Map (or does it?)

[vlad via llvm-dev]

Hello, list

I am not quite sure if what I'm experiencing is a bug or intentional 
behavior.

In the code below the result of a function call is a deopt arg to 
llvm.experimental.gc.statepoint
(http://llvm.org/docs/Statepoints.html#llvm-experimental-gc-statepoint-intrinsic).
Therefore a Stack Map containing location of this variable is created 
upon code generation.

Here's the complete example:

     define i64 addrspace(1)* @func() {
         %p = inttoptr i64 42 to i64 addrspace(1)*
         ret i64 addrspace(1)* %p
     }

     define i8 @main() #0 gc "statepoint-example" {
         %result = call i64 addrspace(1)* @func()

         %token = call i32 (i64, i32, i64 addrspace(1)* ()*, i32, i32, 
...) @llvm.experimental.gc.statepoint.p0f_p1i64f (
             i64 111, i32 0,
             i64 addrspace(1)* ()* @func,
             i32 0, i32 0, i32 0,
             i32 1,
             i64 addrspace(1)* %result) ; the only deopt arg


         %b = ptrtoint i64 addrspace(1)* %result to i64
         %c = trunc i64 %b to i8
         ret i8 %c
     }


     declare i32 @llvm.experimental.gc.statepoint.p0f_p1i64f(i64, i32, 
i64 addrspace(1)* ()*, i32, i32, ...)
     declare i64 addrspace(1)* @llvm.experimental.gc.result.p1i64(i32)

     attributes #0 = { "no-frame-pointer-elim"="true" }

I compile with `llc -O3 -x86-asm-syntax=intel`.

Here is the meat of the emitted asm:
     call    func
     mov rbx, rax
     mov qword ptr [rbp - 16], rbx
     call    func

Here is the corresponding Stack Map Location:
     .byte   2
     .byte   8
     .short  7
     .long   0
Which means, according to 
http://llvm.org/docs/StackMaps.html#stack-map-format, that it's a Direct 
location rsp + 0 (rsp has DWARF register number 7).
Which I find is not exactly true, as it should rather be an Indirect 
location [rsp + 0], or better yet, considering I specified 
"no-frame-pointer-elim"="true", [rbp - 16].

The only explanation about direct locations in the doc is "If an alloca 
value is passed directly to a stack map intrinsic, then LLVM may fold 
the frame index into the stack map as an optimization to avoid 
allocating a register or stack slot. These frame indices will be encoded 
as Direct locations in the form BP + Offset." And as far as I can see 
it's not the case here.

I have a new version of LLVM which I built yesterday.

Please help me understand what's happening here. Thanks in advance