Add explicit template instantiation declarations.

[tkoeppe]

Summary

Explicit instantiations should be declared. Found with -Wundefined-func-template.

[tkoeppe]

Updated diff to one made with -U9999.

[tkoeppe]

I don't have commit access. I'd welcome if someone could commit this change.

Many thanks!

[dblaikie]

Looks good - maybe include info in the description mentioning that the explicit instantiation declarations match existing explicit instantiation definitions in the .cpp file. (I'll include that when I commit in a minute)

mlir/include/mlir/IR/Dominance.h

 #ifndef MLIR_IR_DOMINANCE_H
 #define MLIR_IR_DOMINANCE_H
 
 #include "mlir/IR/RegionGraphTraits.h"
 #include "llvm/Support/GenericDomTree.h"
 
 extern template class llvm::DominatorTreeBase<mlir::Block, false>;
 extern template class llvm::DominatorTreeBase<mlir::Block, true>;
+extern template class llvm::DomTreeNodeBase<mlir::Block>;
 
 namespace mlir {
 using DominanceInfoNode = llvm::DomTreeNodeBase<Block>;
 class Operation;
 
 namespace detail {
 template <bool IsPostDom>
 class DominanceInfoBase {
protected:
   /// "hasSSADominance" bit. This map does not contain dominator trees for
   /// single block CFG regions, but we do want to cache the "hasSSADominance"
   /// bit for them. We may also not have computed the DomTree yet. In either
   /// case, the DomTree is just null.
   ///
   mutable DenseMap<Region *, llvm::PointerIntPair<DomTree *, 1, bool>>
       dominanceInfos;
 };
+
+extern template class DominanceInfoBase</*IsPostDom=*/true>;
+extern template class DominanceInfoBase</*IsPostDom=*/false>;
 } // namespace detail
 
 /// A class for computing basic dominance information. Note that this
 /// class is aware of different types of regions and returns a
 /// region-kind specific concept of dominance. See RegionKindInterface.
 class DominanceInfo : public detail::DominanceInfoBase</*IsPostDom=*/false> {
 public:
   using super::super;