[MLIR] Specify namespace for standard dialect using cppNamespace field

[andidr]

Summary

The ::mlir namespace for operations from standard is currently
defined by enclosing the header file generated from the ODS in
Ops.td in a namespace in Ops.h. However, when referencing
operations from Ops.td in other TableGen files, this causes the
generated C++ code to refer to classes from the global namespace
instead of ::mlir.

By defining the namespace through the cppNamespace field for
StandardOps_Dialect directly in Ops.td instead, the ODS
becomes reusable in other TableGen files through simple
inclusion.

[andidr]

Not sure why some of the unit tests fail. To me this looks unrelated to the patch. Is there any way to trigger re-running the tests?

[andidr]

Rebased diff to HEAD to trigger re-execution of tests.

[mehdi_amini]

Not sure why some of the unit tests fail. To me this looks unrelated to the patch. Is there any way to trigger re-running the tests?

It's not uncommon, feel free to ignore when the tests are clearly unrelated.

mlir/include/mlir/Dialect/StandardOps/IR/Ops.h

 class OpBuilder;
 class PatternRewriter;
 
 /// Return the list of Range (i.e. offset, size, stride). Each Range
 /// entry contains either the dynamic value or a ConstantIndexOp constructed
 /// with `b` at location `loc`.
 SmallVector<Range, 8> getOrCreateRanges(OffsetSizeAndStrideOpInterface op,
                                         OpBuilder &b, Location loc);
+} // namespace mlir
 
 #define GET_OP_CLASSES
 #include "mlir/Dialect/StandardOps/IR/Ops.h.inc"
 
 #include "mlir/Dialect/StandardOps/IR/OpsDialect.h.inc"
 
+namespace mlir {
 /// This is a refinement of the "constant" op for the case where it is
 /// returning a float value of FloatType.
 ///
 ///   %1 = "std.constant"(){value: 42.0} : bf16
 ///
 class ConstantFloatOp : public ConstantOp {
 public:
   using ConstantOp::ConstantOp;

mlir/include/mlir/Dialect/StandardOps/IR/Ops.td

 include "mlir/Interfaces/CastInterfaces.td"
 include "mlir/Interfaces/ControlFlowInterfaces.td"
 include "mlir/Interfaces/SideEffectInterfaces.td"
 include "mlir/Interfaces/VectorInterfaces.td"
 include "mlir/Interfaces/ViewLikeInterface.td"
 
 def StandardOps_Dialect : Dialect {
   let name = "std";
-  let cppNamespace = "";
+  let cppNamespace = "::mlir";
   let hasConstantMaterializer = 1;
   // TODO: This dependency is needed to handle memref ops in the
   // canonicalize pass and should be resolved.
   let dependentDialects = ["memref::MemRefDialect"];
 }
 
 // Base class for Standard dialect ops.
 class Std_Op<string mnemonic, list<OpTrait> traits = []> :