Divide by zero in GetPartReflection when constant buffers have zero-sized arrays.

[johnhable]

Description
There is an issue with a divide by zero when gathering reflection data. In particular, GetPartReflection() is causing a divide by zero exception.

When looking at the shader code, it looks like there was a bug in the raw shader data, with a zero sized array. The compilation was succeeding, but crashing with divide by zero when getting reflection. There was a struct that looked like this:

struct MaterialData
{
float3 diffuseColor;
...
uint4 srv_info[0];
};

ConstantBuffer s_MaterialCb : register(b0,space2);

Removing the srv_info struct fixed it. After discussion, it appears that this line was causing the divide by zero:

https://github.com/microsoft/DirectXShaderCompiler/blob/main/lib/HLSL/DxilContainerReflection.cpp#L997

Steps to Reproduce
While I don't have a full repro case, I can share the specific shader privately if it would help.

Actual Behavior
The output is a divide by zero exception in GetPartReflection().

Environment

• DXC version: July 2024
• Host Operating System: Windows 10, Version 22H2, OS Build 19045.5011