[LLVMdev] [NVPTX] For linkonce_odr NVPTX generates .weak, but even newest PTXAS can't handle it

[Dmitry N. Mikushin]

Dear LLVM NVPTX maintainers,

Just to have the issue recorded, I don't know how important it is:

clang generates linkonce_odr out of __inline__, and NVPTX generates .weak
out of linkonce_odr (how it happens - a big question, btw, because I can't
find anything related in NVPTX asm printer - does it chain to some other
printer?), and finally ptxas (both 4.2 and 5) fails to compile it to cubin.
Below is the test case:

> cat test3.cu

__inline__ __attribute__((device)) __attribute__((used)) void test()
{
    return;
}

> clang -cc1 -emit-llvm -triple ptx64-unknown-unknown -fcuda-is-device
test3.cu -o test3.ll
> cat test3.ll
; ModuleID = 'test3.cu'
target datalayout = "e-p:64:64-i64:64:64-f64:64:
64-n1:8:16:32:64"
target triple = "ptx64-unknown-unknown"

@llvm.used = appending global [1 x i8*] [i8* bitcast (void ()* @_Z4testv to
i8*)], section "llvm.metadata"

define linkonce_odr ptx_device void @_Z4testv() nounwind inlinehint {
entry:
  ret void
}

> llc -march=nvptx64 -mcpu=sm_20 test3.ll -o test3.ptx
> cat test3.ptx

//
// Generated by LLVM NVPTX Back-End
//

.version 3.0
.target sm_20, texmode_independent
.address_size 64


    .weak    _Z4testv
.func _Z4testv(

)                                       // @_Z4testv
{
    .reg .pred %p<396>;
    .reg .s16 %rc<396>;
    .reg .s16 %rs<396>;
    .reg .s32 %r<396>;
    .reg .s64 %rl<396>;
    .reg .f32 %f<396>;
    .reg .f64 %fl<396>;

// BB#0:                                // %entry
    ret;
}

1) ptxas @ CUDA 4.2:

> ptxas -arch=sm_20 -m64 test3.ptx -o -

ptxas test3.ptx, line 10; fatal   : Parsing error near '.weak': syntax error
ptxas fatal   : Ptx assembly aborted due to errors

2) ptxas @ CUDA 5:

> ~/cuda/bin/ptxas -arch=sm_20 -m64 test3.ptx -o -

ptxas test3.ptx, line 10; error   : Feature '.weak directive' requires PTX
ISA .version 3.1 or later
ptxas test3.ptx, line 10; fatal   : Parsing error near '_Z4testv': syntax
error
ptxas fatal   : Ptx assembly aborted due to errors

3) ptxas @ CUDA 5, changed .version to 3.1: still error, because according
to 3.1 PTX spec, .weak must be followed by .func:

> ~/cuda/bin/ptxas -arch=sm_20 -m64 test3.ptx -o -

ptxas test3.ptx, line 10; fatal   : Parsing error near '_Z4testv': syntax
error
ptxas fatal   : Ptx assembly aborted due to errors

Best,
- Dima.
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