commit d43294521aa2af71910d2a8a8fef56a7e5d36c91
author Scott Todd <scotttodd@google.com> Wed Aug 19 12:23:32 2020 -0700
committer GitHub <noreply@github.com> Wed Aug 19 12:23:32 2020 -0700
tree 7b56ac24c2ebe4061fff2945471fe3ae0b19ff4d
parent 403635de58217376fc43874b2e2f29f110f582b0

Move hal.executable.entry_point ops into hal.executable.target. (#2893)

The HAL transformation pass pipeline "materializes interfaces" then "translates executables" for each configured target ([source](https://github.com/google/iree/blob/d7f61a1510aeee066e34ebfadf13f7651aea4de4/iree/compiler/Dialect/HAL/Transforms/Passes.cpp#L46-L58)). As part of its executable translation, the VulkanSPIRV target "splits" dispatch functions using [SplitDispatchFunctionPass](https://github.com/google/iree/blob/d7f61a1510aeee066e34ebfadf13f7651aea4de4/iree/compiler/Conversion/LinalgToSPIRV/SplitDispatchFunctionPass.cpp), creating a schedule of `spv.EntryPoint` ops to dispatch in sequence when `recordDispatch()` is called ([source](https://github.com/google/iree/blob/d7f61a1510aeee066e34ebfadf13f7651aea4de4/iree/compiler/Dialect/HAL/Target/VulkanSPIRV/VulkanSPIRVTarget.cpp#L321-L370)).

For https://github.com/google/iree/issues/1890, we want to change dispatch ops from using loose ordinals for entry points:
```
hal.command_buffer.dispatch %arg0, %arg1, entry_point = 0, workgroup_xyz = ...
```
to using nested references:
```
hal.command_buffer.dispatch %arg0, %arg1, entry_point = @MyExecutable::EntryPoint, workgroup_xyz = ...
```

To use references in that format, the VulkanSPIRV target should create new `hal.executable.entry_point` ops which can be referenced whenever it splits dispatch functions. However, entry points are currently placed on `hal.executable` ops, which can contain multiple `hal.executable.target` ops (e.g. several for "vulkan" and one for "vmla"). Thus, this PR moves entry points down into `hal.executable.target` ops so that each target can have more control over how it sets up its entry points.

---

I explored a few different ways to structure the passes involved as part of this work, each with some tradeoffs. Happy to make changes now that I have a better handle on how this all fits together.