commit fa16b40b0fb446262da9ac7f194d551ef68bb554
author Scott Todd <scotttodd@google.com> Fri Sep 11 08:07:02 2020 -0700
committer GitHub <noreply@github.com> Fri Sep 11 08:07:02 2020 -0700
tree 7565c4a7403fb9044cff31b389ef0cbf34a3d0cf
parent 465279e585ebb0bec7c2213ba043a3db74db48e2

Refactor semaphore use in async and sync public ABI functions. (#3118)

This makes async the "default", with sync wrapping async, instead of the other way around. Now we can push semaphores down further into the compiler (e.g. to remove hal.ex.submit_and_wait).

Progress on https://github.com/google/iree/issues/1285

---

If the test is hard to read, here's a sample from simple.mlir's translation:
* Note how the `$sync` function creates a semaphore to pass into the `$async` function and waits for it to be incremented from `0` to `1` before returning. The `$async` function still waits and signals, but could instead pass the semaphores into the raw function for a `hal.submit`, removing the need for `hal.ex.submit_and_wait`.

Before:
```mlir
  func @abs$sync(%arg0: !hal.buffer_view) -> !hal.buffer_view attributes {iree.abi.stub, iree.module.export = "abs", iree.reflection = {f = "I6!B3!t6R6!B3!t6", fv = "1"}} {
    %buffer = hal.buffer_view.buffer %arg0 : !hal.buffer
    %0 = call @abs(%buffer) : (!hal.buffer) -> !hal.buffer
    %view = hal.buffer_view.create %0, shape = [], element_type = 16777248 : !hal.buffer_view
    return %view : !hal.buffer_view
  }
  func @abs$async(%arg0: !hal.semaphore, %arg1: index, %arg2: !hal.buffer_view, %arg3: !hal.semaphore, %arg4: index) -> !hal.buffer_view attributes {iree.module.export = "abs$async"} {
    %0 = hal.semaphore.await %arg0, min_value = %arg1 : i32
    hal.check_success %0, "semaphore wait failed"
    %1 = call @abs$sync(%arg2) : (!hal.buffer_view) -> !hal.buffer_view
    hal.semaphore.signal %arg3, value = %arg4
    return %1 : !hal.buffer_view
  }
```

After:
```mlir
  func @abs$async(%arg0: !hal.semaphore, %arg1: index, %arg2: !hal.buffer_view, %arg3: !hal.semaphore, %arg4: index) -> !hal.buffer_view attributes {iree.module.export = "abs$async"} {
    %0 = hal.semaphore.await %arg0, min_value = %arg1 : i32
    hal.check_success %0, "semaphore wait failed"
    %buffer = hal.buffer_view.buffer %arg2 : !hal.buffer
    %1 = call @abs(%buffer) : (!hal.buffer) -> !hal.buffer
    %view = hal.buffer_view.create %1, shape = [], element_type = 16777248 : !hal.buffer_view
    hal.semaphore.signal %arg3, value = %arg4
    return %view : !hal.buffer_view
  }
  func @abs$sync(%arg0: !hal.buffer_view) -> !hal.buffer_view attributes {iree.abi.stub, iree.module.export = "abs", iree.reflection = {f = "I6!B3!t6R6!B3!t6", fv = "1"}} {
    %c0 = constant 0 : index
    %c1 = constant 1 : index
    %dev = hal.ex.shared_device : !hal.device
    %semaphore = hal.semaphore.create %dev, initial_value = %c0 : !hal.semaphore
    %0 = call @abs$async(%semaphore, %c0, %arg0, %semaphore, %c1) : (!hal.semaphore, index, !hal.buffer_view, !hal.semaphore, index) -> !hal.buffer_view
    %1 = hal.semaphore.await %semaphore, min_value = %c1 : i32
    hal.check_success %1, "semaphore wait failed"
    return %0 : !hal.buffer_view
  }
```