[SPIR-V] Counter is emitted when RWStructuredBuffer is passed into a function

[Raikiri]

Description

[[vk::binding(0, 0)]]
StructuredBuffer<int> buf;

void Func(StructuredBuffer<int> b){}

void main()
{
  Func(buf);
}

Compiling with

dxc -spirv -T ps_6_0 -E main `"$srcPath`" -fspv-preserve-interface -fspv-preserve-bindings -Fo `"$dstPath`"

This code emits a binding for buf, but also for counter.var.buf. If I comment out the function call Func(buf), the second binding disappears.

Seems possibly related to #3287 ?

Environment

• DXC version libdxcompiler.so: 1.8(dev;0-00000000); libdxil.so: 1.8
• Host Operating System NixOS (not sure how this is relevant)

[s-perron]

This is expected. When passing the buffer to a function, we cannot know what the function will do with the buffer. The counter has to be created and passed along in case. Typically it would be removed during optimization if it is not actually needed.

However, you have the option to preserve the variable. The optimizer will leave it at your request.

[Raikiri]

I use the flag "preserve inteface" to preserve the interface that I defined, not the interface that the compiler decided to generate for its internal purposes. In fact, what the compiler does in this case is the opposite of preserving the interface that I defined.