[PATCH] [NVPTX] noop when kernel pointers are already global

[Justin Holewinski]

Hi Tobias,

One thing to keep in mind is that the CUDA interface expects kernel parameters to be in the generic address space.  If you write kernels that pass arguments as global memory pointers, you are technically violating the contract between host and device.  Now, this just so happens to work since the global->generic and generic->global pointer conversions are no-ops, but as far as I know this is not actually guaranteed and may not be true in the future.

> On Jun 26, 2015, at 6:36 PM, Jingyue Wu <jingyue at google.com> wrote:
> 
> REPOSITORY
>  rL LLVM
> 
> http://reviews.llvm.org/D10779
> 
> Files:
>  llvm/trunk/lib/Target/NVPTX/NVPTXLowerKernelArgs.cpp
>  llvm/trunk/test/CodeGen/NVPTX/lower-kernel-ptr-arg.ll
> 
> Index: llvm/trunk/lib/Target/NVPTX/NVPTXLowerKernelArgs.cpp
> ===================================================================
> --- llvm/trunk/lib/Target/NVPTX/NVPTXLowerKernelArgs.cpp
> +++ llvm/trunk/lib/Target/NVPTX/NVPTXLowerKernelArgs.cpp
> @@ -132,6 +132,10 @@
>   assert(!Arg->hasByValAttr() &&
>          "byval params should be handled by handleByValParam");
> 
> +  // Do nothing if the argument already points to the global address space.
> +  if (Arg->getType()->getPointerAddressSpace() == ADDRESS_SPACE_GLOBAL)
> +    return;
> +
>   Instruction *FirstInst = Arg->getParent()->getEntryBlock().begin();
>   Instruction *ArgInGlobal = new AddrSpaceCastInst(
>       Arg, PointerType::get(Arg->getType()->getPointerElementType(),
> Index: llvm/trunk/test/CodeGen/NVPTX/lower-kernel-ptr-arg.ll
> ===================================================================
> --- llvm/trunk/test/CodeGen/NVPTX/lower-kernel-ptr-arg.ll
> +++ llvm/trunk/test/CodeGen/NVPTX/lower-kernel-ptr-arg.ll
> @@ -16,5 +16,16 @@
>   ret void
> }
> 
> -!nvvm.annotations = !{!0}
> +define void @kernel2(float addrspace(1)* %input, float addrspace(1)* %output) {
> +; CHECK-LABEL: .visible .entry kernel2(
> +; CHECK-NOT: cvta.to.global.u64
> +  %1 = load float, float addrspace(1)* %input, align 4
> +; CHECK: ld.global.f32
> +  store float %1, float addrspace(1)* %output, align 4
> +; CHECK: st.global.f32
> +  ret void
> +}
> +
> +!nvvm.annotations = !{!0, !1}
> !0 = !{void (float*, float*)* @kernel, !"kernel", i32 1}
> +!1 = !{void (float addrspace(1)*, float addrspace(1)*)* @kernel2, !"kernel", i32 1}
> 
> EMAIL PREFERENCES
>  http://reviews.llvm.org/settings/panel/emailpreferences/
> <D10779.28605.patch>

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