[all-commits] [llvm/llvm-project] 350b4d: [mlir][IR] Hash nesting structure in OperationFing...

[Matthias Springer via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 350b4d05e85ece30bd9f02be410b4bcb90af7a42
      https://github.com/llvm/llvm-project/commit/350b4d05e85ece30bd9f02be410b4bcb90af7a42
  Author: Matthias Springer <me at m-sp.org>
  Date:   2023-05-24 (Wed, 24 May 2023)

  Changed paths:
    M mlir/lib/IR/OperationSupport.cpp

  Log Message:
  -----------
  [mlir][IR] Hash nesting structure in OperationFingerPrint

The following ops currently have the same finger print, even though they are different:
```
func.func @test() {
  "test.foo"() ({
    "test.bar"() : () -> ()
  }) : () -> ()
}
```
And:
```
func.func @test() {
  "test.bar"() : () -> ()
  "test.foo"() ({ }) : () -> ()
}
```

The SHA1 hash used in OperationFingerPrint is order-sensitive, but the ops are hashed in the same order (post-order traversal), so the hash is the same. Switching to pre-order traversal does not solve the issue; a similar example, where IR differs just in its nesting structure, can be constructed.

The problem is solved by hashing the parent op pointer. (Alternatively, a traversal over the IR that hashes scope markers (`{}`) could be used.)

Differential Revision: https://reviews.llvm.org/D151306