Why is the "omp" dialect loaded by default?

dpotop · September 24, 2020, 8:47am

Hello,

I wrote a dialect, along with its compiler. This compiler registers and loads two other dialects: std and llvm, which it uses as lowering targets. But for some reason, when I call context.getLoadedDialects() the omp dialect is listed as well. I guess this is why when linking I need to include libMLIROpenMP…

Is there a way to remove it?

Best,
Dumitru

SouraVX · September 24, 2020, 12:42pm

Could please let us know the motivation behind doing this ? why do you want to remove it ?
+
@kiranchandramohan @mehdi_amini

kiranchandramohan · September 24, 2020, 1:34pm

Thanks @dpotop for your question.

I think this happens because the OpenMP dialect is listed as a dependency for the LLVM dialect. There is actually no dependency, it is just that the tool that is used to translate the LLVM dialect is also capable of translating the mix of OpenMP+LLVM dialect. This is currently listed as a FIXME, see link below.

github.com

llvm/llvm-project/blob/a6a6ccfc4c8b348d6d534657e16bb7504b9f2888/mlir/include/mlir/Dialect/LLVMIR/LLVMOpBase.td#L30


//===----------------------------------------------------------------------===//
// LLVM Dialect.
//===----------------------------------------------------------------------===//

def LLVM_Dialect : Dialect {
  let name = "llvm";
  let cppNamespace = "::mlir::LLVM";

  /// FIXME: at the moment this is a dependency of the translation to LLVM IR,
  /// not really one of this dialect per-se.
  let dependentDialects = ["omp::OpenMPDialect"];

  let hasRegionArgAttrVerify = 1;
  let hasOperationAttrVerify = 1;
  let extraClassDeclaration = [{
    /// Name of the data layout attributes.
    static StringRef getDataLayoutAttrName() { return "llvm.data_layout"; }

    /// Verifies if the given string is a well-formed data layout descriptor.
    /// Uses `reportError` to report errors.
    static LogicalResult verifyDataLayoutString(

dpotop · September 24, 2020, 2:18pm

@kiranchandramohan Thanks for this explanation.
@SouraVX I’m a scientist, when there’s stuff around in my work and I don’t understand why I tend to wonder why.

mehdi_amini · September 25, 2020, 5:07am

We could lift this restriction by fixing the translator to LLVM IR, it is just an implementation quirks right now.

mehdi_amini · September 26, 2020, 2:18am

Sent: https://reviews.llvm.org/D88351 to make it not loaded by default. It is still a link dependency to export to LLVM IR though.