[SPIR-V] Improperly aligned OpLoad/OpStore for structures with 64-bit scalar types

[krisvers]

Description
When using vk::RawBufferLoad<T> when T is a structure containing at least one 64-bit scalar (such as uint64_t or double, but not uint2 or float2), the generated SPIR-V improperly tries to load from the address using a 4-byte alignment which should be 8-byte.

Steps to Reproduce

• Source Code: https://godbolt.org/z/o9e1djnce
  Or Simplified Code:

  struct StructureWith64BitScalarMember {
    uint64_t member;
    double member2; //also fails
  };
  
  void main() {
    uint64_t someAddress;
    /* line below produces invalid SPIR-V */
    StructureWith64BitScalarMember data64 = vk::RawBufferLoad<StructureWith64BitScalarMember>(someAddress);
    vk::RawBufferStore<StructureWith64BitScalarMember>(someAddress, data64);
  }

• Command Run: dxc.exe -T cs_6_0 -E main -spirv source.hlsl -Fo out.spv (note: my dxc executable was sourced from LunarG's VulkanSDK version 1.4.335.0)

Actual Behavior 1

StructureWith64BitScalarMember data64 = vk::RawBufferLoad<StructureWith64BitScalarMember>(someAddress);

The above HLSL code (see the source code link in Steps to Reproduce) compiles to %75 = OpLoad %StructureWith64BitScalarMember %74 Aligned 4, which is then validated within DXC's pipeline and is found to be invalid.

fatal error: generated SPIR-V is invalid: [VUID-StandaloneSpirv-PhysicalStorageBuffer64-06314] Memory accesses Aligned operand value 4 is too small, the largest scalar type is 8 bytes.
  %75 = OpLoad %StructureWith64BitScalarMember %74 Aligned 4

note: please file a bug report on https://github.com/Microsoft/DirectXShaderCompiler/issues with source code if possible

Actual Behavior 2

vk::RawBufferStore<StructureWith64BitScalarMember>(someAddress, data64);

The above HLSL code (see the source code link in Steps to Reproduce) compiles to OpStore %57 %58 Aligned 4, which is then validated within DXC's pipeline and is found to be invalid.

fatal error: generated SPIR-V is invalid: [VUID-StandaloneSpirv-PhysicalStorageBuffer64-06314] Memory accesses Aligned operand value 4 is too small, the largest scalar type is 8 bytes.
  OpStore %57 %58 Aligned 4

note: please file a bug report on https://github.com/Microsoft/DirectXShaderCompiler/issues with source code if possible

Environment

• DXC version: dxcompiler.dll: 1.10 - 1.8.0.5123 (3f85295cf)
• Host Operating System: Windows 11 25H2 (OS Build 26200.8655)

NOTE
Both actual behaviors are not visible at the same time. This is because when a single SPIR-V validation check fails, no further validation is continued. So, when the load is determined to be invalid, it doesn't attempt to report the equally as invalid store later.