[SPIR-V] Crash when accessing buffer from array of buffers

[jaoel]

Description
The SPIR-V optimizer crashes when accessing a buffer from an array of buffers which has been assigned to a variable.

Steps to Reproduce
Minimal example derived from a real world shader that suffers from the crash:

ByteAddressBuffer inputBuffers[16] : register(t0);

struct MyStruct
{
	ByteAddressBuffer myBuffers[16];
};

[numthreads(32, 1, 1)]
void main()
{
	MyStruct ms;
	ms.myBuffers = inputBuffers;
	ByteAddressBuffer buffer = ms.myBuffers[0]; // < This line causes crash
}

I managed to strip the example even more to just these two lines, but the location of the crash is slightly different so I'll include both examples for completeness:

[numthreads(32, 1, 1)]
void main()
{
	ByteAddressBuffer buffers[16];
	ByteAddressBuffer buffer = buffers[0]; // < This line causes crash
}

Everything is compiled with command line options: -E "main" -T cs_6_0 -spirv

Actual Behavior
Both examples causes a crash in SPIRV-Tools Pass::GenerateCopy()
The first example produces an assert "Don't know how to copy this type. Code is likely illegal."
The second example attempts to read nullptr.

Environment

• DXC version dxcompiler.dll: 1.8 - 1.7.0.14383 (main, ad3958c2d)
• Host Operating System Windows 10 64-bit

[s-perron]

The is a bug in the SPIR-V code generation in DXC. Local ByteAddressBuffers are suppose to be treated as pointers to the ByteAddressBuffers in the uniform storage class. This is how buffers and buffer are declared:

    %buffers = OpVariable %_ptr_Function__ptr_Uniform__arr_type_ByteAddressBuffer_uint_16 Function
     %buffer = OpVariable %_ptr_Function__ptr_Uniform_type_ByteAddressBuffer Function

However, when implement the copy of the array element into buffer we try to copy the ByteAddressBuffer itself, and not a pointer to it.

         %21 = OpLoad %_ptr_Uniform__arr_type_ByteAddressBuffer_uint_16 %buffers
         %22 = OpAccessChain %_ptr_Uniform_type_ByteAddressBuffer %21 %int_0
         %23 = OpLoad %type_ByteAddressBuffer %22  ; <-- We load the entire ByteAddressBuffer
               OpStore %buffer %23 ; <-- And we try to store it. We should store %22 instead.

[jaoel]

Thanks for looking into this! Unfortunately this fix does not solve the issues in the first example I gave.
Storing an array of buffers in a struct and later accessing those buffers still produces a read access violation when compiling.