[PATCH] D138531: [PATCH] [NVPTX] Backend support for variadic functions

[Artem Belevich via Phabricator via llvm-commits]

tra added a comment.

> Note that aggregates passed by value as variadic arguments are not currently supported.

What happens when a user does try to pass an aggregate as a var arg?



================
Comment at: llvm/lib/Target/NVPTX/NVPTXAsmPrinter.cpp:1676
+      O << ",\n";
+    O << "\t.param .align 8 .b8 %VAParam[]";
+  }
----------------
pavelkopyl wrote:
> tra wrote:
> > What determines the alignment here? 
> > NVIDIA does not seem to specify anything regarding alignment here and their example shows `align 4`:
> > https://docs.nvidia.com/cuda/parallel-thread-execution/index.html#kernel-and-function-directives-func
> > 
> > 
> It seems the documentation is a little bit outdated, because NVCC 11.7 generates .align 8 for the last parameter (unsized array): https://godbolt.org/z/7W7YThMf8
> 
The question remains. Do we set alignment to 8 because that's what NVCC does or is there some other reason behind it?
I.e. should it follow the alignment guarantees provided by e.g. `malloc` which returns a pointer sufficiently aligned to access any type. 

I think this should be retrieved from DataLayout or TargetInfo, instead of being hardcoded here.
Based on `NVPTXTargetLowering::getFunctionParamOptimizedAlign`, we may have argument alignment as high as 16.


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  https://reviews.llvm.org/D138531/new/

https://reviews.llvm.org/D138531