Shader compiler doesn't generate a loop where one should exist

Description

Moved from internal bug 32923212

See https://godbolt.org/z/nGYxzTPn1

uint2 WaveMatchAdam(uint value)
{
    do
    {
        bool isOurValue = (WaveReadLaneFirst(value) == value);
        if (isOurValue)
        {
            return WaveActiveBallot(isOurValue).xy;
        }
    } while (true);
}

StructuredBuffer<uint> values : register(t0);
RWStructuredBuffer<uint2> matchMasks : register(u0);

[RootSignature("SRV(t0), UAV(u0)")]
[numthreads(64,1,1)]
void main(uint DTid : SV_DispatchThreadID)
{
    uint value = values[DTid.x];
    matchMasks[DTid.x] = WaveMatchAdam(value);
}

Generated DXIL doesn't contain a loop.

Steps to Reproduce

See https://godbolt.org/z/nGYxzTPn1

Environment

• libdxcompiler.so: 1.8(dev;1-b197bec6)

Start with the Godbolt reproduction at https://godbolt.org/z/nGYxzTPn1 and inspect the generated DXIL from libdxcompiler.so 1.8. Compare it with the HLSL do-while loop in the report and trace the compiler stage where the loop is lost. Done when the reproduction generates DXIL containing the expected loop.