This patch only shows a way how to custom lowering the constrained fma operation.
What does this patch do:
- Expand SDNodeFlags APIs to set up SDNodeFlags at the initial DAG build phase when reading the constrained fps metadata data.
- AMDGPU backend sets up resister modes based on retrieved SDNodeFlags.
This change will fail on all platforms except AMDGPU as you have this patch written. If you need target-specific behavior here, we'll need a target hook of some kind.