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Fix accuracy issue for double alias #950

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Fix accuracy issue for double alias #950

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Commits on Oct 12, 2023

  1. Temporary commit at 10/5/2023, 2:10:31 PM 

    Differential Revision:
D49759512

test_codegen

fbshipit-source-id: c2d9f9ee4aeda516e56229b5369bf46cc313e256
    @ColinPeppler @facebook-github-bot
    ColinPeppler authored and facebook-github-bot committed Oct 12, 2023
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  2. Fix accuracy issue for double output alias (facebookincubator#950) 

    Summary:
Pull Request resolved: facebookincubator#950

## Problem

Here's an edge case for AIT. Suppose we have two outputs, and both are view on the same tensor. Atm, AIT will not provide accurate results for output0.

```
some-tensor  <--view-- output0
         ^------view-- ouptut1

void SetUpInputOutput() {
  input_x = static_cast<decltype(input_x)>(params_[0].ptr);
  elementwise_0_0 = static_cast<decltype(elementwise_0_0)>(params_[2].ptr);
  output_0 = elementwise_0_0;
  output_1 = elementwise_0_0;
}

void DeviceToDeviceCopies(stream) {
  // empty
}
```

Why doesn't AIT provide accurate results for output0? Because notice how `params_[1]` isn't assigned to anything.

## Solution
Use a D2D copy to pass data from `params_[2]` to `params_[1]`. We do this by checking to see if the view is aliased by another output.
* If yes, then run a D2D copy.
* If no, don't worry about this output.

## Refactor
We refactor `_codegen_output_tensor` by combining the `external_tensor` case with the `is_view` case.

Differential Revision: D50202241

fbshipit-source-id: 599cc609dcb11f92e432479f2f3214236f6d68c5
    @ColinPeppler @facebook-github-bot
    ColinPeppler authored and facebook-github-bot committed Oct 12, 2023
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    2b87bc1 View commit details
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