failed to legalize SPIR-V: Variable cannot be replaced: invalid index on embedded loop

[MichelVachon]

Description
A shader does not compile with "-fspv-flatten-resource-arrays" with a mixture of for loops and ifs

Note: the shader compiles when the if() condition is moved inside the inner loop.

Steps to Reproduce
Compile the following shader

RWTexture2D HZBDstTextures[16];
[numthreads(8, 8, 1)]
void main(uint3 groupId : SV_GroupID)
{
[unroll]
for (uint srcTextureID = 0; srcTextureID < 16; srcTextureID++)
{
[branch]
if (srcTextureID == groupId.z)
{
[unroll]
for (uint mipOffset = 1; mipOffset < 4; mipOffset++)
{
const uint dstTextureID = srcTextureID + mipOffset;
HZBDstTextures[dstTextureID][uint2(0, 0)] = 2.2f;
}
}
}
}

With the following command line:
dxc.exe" /T cs_6_0 -spirv -fspv-flatten-resource-arrays

Actual Behavior
The following error message is reported:
fatal error: failed to legalize SPIR-V: Variable cannot be replaced: invalid index
%87 = OpAccessChain %_ptr_UniformConstant_type_2d_image %HZBDstTextures %85
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(5373-c4d8f4f9)(1.10.2605.37) - 1.10.2605.37 (c4d8f4f)
• Host Operating System Windows 11 Enterprise 24H2