[clang] [llvm] [SPIRV] Use AMDGPU ABI for AMDGCN flavoured SPIRV (PR #169865)

[Marcos Maronas via llvm-commits]

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@@ -374,7 +374,10 @@ bool SPIRVCallLowering::lowerFormalArguments(MachineIRBuilder &MIRBuilder,
         buildOpDecorate(VRegs[i][0], MIRBuilder,
                         SPIRV::Decoration::FuncParamAttr, {Attr});
       }
-      if (Arg.hasAttribute(Attribute::ByVal)) {
+      if (Arg.hasAttribute(Attribute::ByVal) ||
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maarquitos14 wrote:

Can we add a comment here explaining why you need this for AMD, so that people can easily understand when reading this code? I fear people might don't understand, or simply think it's wrong, to lower `ByRef` to `ByVal`.

https://github.com/llvm/llvm-project/pull/169865