<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/77739>77739</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            Issue with CoroEarlyPass Pass Introducing New Undefined Behavior in LLVM Transformation
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            new issue
      </td>
    </tr>

    <tr>
      <th>Assignees</th>
      <td>
      </td>
    </tr>

    <tr>
      <th>Reporter</th>
      <td>
          wyanzhao
      </td>
    </tr>
</table>

<pre>
    Consider that we have a source code file named `test.ll` with the following contents:
```llvm
define ptr @f(i32 %n) {
  ret ptr null;
}

declare void @llvm.coro.resume(ptr)

define i32 @main() {
  %hdl = call ptr @f(i32 4)
  call void @llvm.coro.resume(ptr %hdl)
  ret i32 0
}
```
After executing the command `llvm-project/build/bin/opt ./test.ll -passes='default<O2>' -print-after-all`, we observe the transformed code resulting from the `CoroEarlyPass` pass in the output:

```llvm
; *** IR Dump After CoroEarlyPass on [module] ***
; ModuleID = './test.ll'
source_filename = "./test.ll"

define ptr @f(i32 %n) {
  ret ptr null
}

declare void @llvm.coro.resume(ptr)

define i32 @main() {
  %hdl = call ptr @f(i32 4)
  %0 = call ptr @llvm.coro.subfn.addr(ptr %hdl, i8 0)
  call fastcc void %0(ptr %hdl)
 ret i32 0
}

; Function Attrs: nocallback nofree nosync nounwind willreturn memory(argmem: read)
declare ptr @llvm.coro.subfn.addr(ptr nocapture readonly, i8) #0

attributes #0 = { nocallback nofree nosync nounwind willreturn memory(argmem: read) }
```

### Issue Description

The `CoroEarlyPass` transformation introduces new instances of undefined behavior in the LLVM IR, particularly when handling functions that return a null pointer in the context of coroutine intrinsics.

### Original Code Behavior:

In the original code's main function, the function `@f(i32 %n)` returns `ptr null`.
The call to `@llvm.coro.resume(ptr %hdl)` with `%hdl` being a null pointer (returned from @f) leads to undefined behavior.

### Transformed Code Behavior:

In the transformed code's main function, `%hdl` (which is ptr null) is used in the expression` %0 = call ptr @llvm.coro.subfn.addr(ptr %hdl, i8 0)`. This call likely leads to undefined behavior due to the dereference of a null pointer.

The result of this call (`%0`) is considered to be "poisoned" due to the undefined behavior of the previous step.

Subsequently, the `call fastcc void %0(ptr %hdl)` with a potentially poisoned `%0` and a null `%hdl` introduces another instance of undefined behavior.

Thus, the `CoroEarlyPass` pass introduces new undefined behaviors in the transformed code, which were not present in the original source code.
</pre>
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