[all-commits] [llvm/llvm-project] 2ac2e9: [mlir][LLVM] Improve lowering of `llvm.byval` func...

[Diego Caballero via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 2ac2e9a5b6c97cbf267db1ef322ed21ebceb2aba
      https://github.com/llvm/llvm-project/commit/2ac2e9a5b6c97cbf267db1ef322ed21ebceb2aba
  Author: Diego Caballero <dieg0ca6aller0 at gmail.com>
  Date:   2024-08-08 (Thu, 08 Aug 2024)

  Changed paths:
    M mlir/include/mlir/Conversion/LLVMCommon/TypeConverter.h
    M mlir/lib/Conversion/FuncToLLVM/FuncToLLVM.cpp
    M mlir/lib/Conversion/LLVMCommon/TypeConverter.cpp
    M mlir/test/Transforms/test-convert-func-op.mlir
    M mlir/test/lib/Conversion/FuncToLLVM/TestConvertFuncOp.cpp

  Log Message:
  -----------
  [mlir][LLVM] Improve lowering of `llvm.byval` function arguments (#100028)

When a function argument is annotated with the `llvm.byval` attribute,
[LLVM expects](https://llvm.org/docs/LangRef.html#parameter-attributes)
the function argument type to be an `llvm.ptr`. For example:

```
func.func (%args0 : llvm.ptr {llvm.byval = !llvm.struct<(i32)>} {
  ...
}
```

Unfortunately, this makes the type conversion context-dependent, which
is something that the type conversion infrastructure (i.e.,
`LLVMTypeConverter` in this particular case) doesn't support. For
example, we may want to convert `MyType` to `llvm.struct<(i32)>` in
general, but to an `llvm.ptr` type only when it's a function argument
passed by value.

To fix this problem, this PR changes the FuncToLLVM conversion logic to
generate an `llvm.ptr` when the function argument has a `llvm.byval`
attribute. An `llvm.load` is inserted into the function to retrieve the
value expected by the argument users.



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