Calling member function on raypayload causes `cast<X>() argument of incompatible type` error with PAQ

[simco50]

Description
When compiling the provided simple shader repro with SM6.7 or above (when PAQ is enabled by default) or with SM6.6 and compiling with -enable-payload-qualifiers, the compiler fails with an "Internal Compiler error".
It seems to be related to PAQ in combination with calling a member function on a raypayload that writes to a member.

Steps to Reproduce
Example in Compiler Explorer: https://godbolt.org/z/qqKedsWv9
Commandlines that reproduce the issue:

• -T lib_6_7
• -T lib_6_8
• -T lib_6_6 -enable-payload-qualifiers

Actual Behavior
The output of the compiler:

Internal Compiler error: cast<X>() argument of incompatible type!
Compiler returned: 29

Environment

• DXC version dxcompiler.dll: 1.8 - 1.8.2403.36 (9c2b82878); dxil.dll: 1.8(101.8.2403.21)
• Host Operating System: Win11 - 22631.3296

[llvm-beanz]

A few bits of extra context. This reproduces back to DXC 1.7.2207 when targeting SM 6.7, so it is not a new regression. The call stack for the exception throw is:

An exception is being thrown from here, because a member function is being accessed but the code assumes all member accesses are field declarations.

This exposes a flaw in the implementation for payload access qualifiers. It incorrectly assumes all member expressions are accessing field declarations whereas here we're accessing a member function declaration.

[damyanp]

Slightly reduced repro: https://godbolt.org/z/bnb9feMv6 - this repro doesn't have any payload qualifiers at all, although passing -enable-payload-qualifiers does trigger it.

Looks like this would affect someone trying to migrate from lib_6_6 to lib_6_7.

[devshgraphicsprogramming]

I've ran into this recently with SPIR-V output as well

struct [raypayload] PrimaryPayload
{
    using generator_t = nbl::hlsl::random::Pcg;

    // alpha is quantized to 10 bits
    bool nextDiscard(const uint32_t quantAlpha)
    {
        const uint32_t bitpattern = pcg()>>22;
        return bitpattern > quantAlpha;
    }

    bool nextDiscard(const float32_t alpha)
    {
        const uint32_t bitpattern = pcg();
        const float32_t xi = (float32_t(bitpattern)+0.5f)/float32_t(0xFFFFFFFF);
        return xi > alpha;
    }

    float32_t3  worldNormal : read(caller) : write(closesthit);
    float32_t   rayDistance : read(caller) : write(closesthit, miss);
    generator_t pcg         : read(anyhit) : write(caller,anyhit);
    MaterialId  materialId  : read(caller) : write(closesthit);

};

as soon as I added a method to a payload struct

[devshgraphicsprogramming]

You can, however put a struct with a method as a member variable in the payload. That works.