[Flang][mlir] add a band-aid to support the creation of mutually recursive types when lowering to LLVM IR

Summary:
This is a temporary implementation to support Flang.  The LLVM-IR parser
will need to be extended in some way to support recursive types.  The
exact approach here is still a work-in-progress.

Unfortunately, this won't pass roundtrip testing yet. Adding a comment
to the test file as a reminder.

Differential Revision: https://reviews.llvm.org/D72542

mlir/include/mlir/Dialect/LLVMIR/LLVMDialect.h

@@ -138,6 +138,47 @@ public:
   static LLVMType getVectorTy(LLVMType elementType, unsigned numElements);
   static LLVMType getVoidTy(LLVMDialect *dialect);
 
+  // Creation and setting of LLVM's identified struct types
+  static LLVMType createStructTy(LLVMDialect *dialect,
+                                 ArrayRef<LLVMType> elements,
+                                 Optional<StringRef> name,
+                                 bool isPacked = false);
+
+  static LLVMType createStructTy(LLVMDialect *dialect,
+                                 Optional<StringRef> name) {
+    return createStructTy(dialect, llvm::None, name);
+  }
+
+  static LLVMType createStructTy(ArrayRef<LLVMType> elements,
+                                 Optional<StringRef> name,
+                                 bool isPacked = false) {
+    assert(!elements.empty() &&
+           "This method may not be invoked with an empty list");
+    LLVMType ele0 = elements.front();
+    return createStructTy(&ele0.getDialect(), elements, name, isPacked);
+  }
+
+  template <typename... Args>
+  static typename std::enable_if_t<llvm::are_base_of<LLVMType, Args...>::value,
+                                   LLVMType>
+  createStructTy(StringRef name, LLVMType elt1, Args... elts) {
+    SmallVector<LLVMType, 8> fields({elt1, elts...});
+    Optional<StringRef> opt_name(name);
+    return createStructTy(&elt1.getDialect(), fields, opt_name);
+  }
+
+  static LLVMType setStructTyBody(LLVMType structType,
+                                  ArrayRef<LLVMType> elements,
+                                  bool isPacked = false);
+
+  template <typename... Args>
+  static typename std::enable_if_t<llvm::are_base_of<LLVMType, Args...>::value,
+                                   LLVMType>
+  setStructTyBody(LLVMType structType, LLVMType elt1, Args... elts) {
+    SmallVector<LLVMType, 8> fields({elt1, elts...});
+    return setStructTyBody(structType, fields);
+  }
+
 private:
   friend LLVMDialect;
 

mlir/lib/Dialect/LLVMIR/IR/LLVMDialect.cpp

@@ -1641,6 +1641,35 @@ LLVMType LLVMType::getStructTy(LLVMDialect *dialect,
                                  isPacked);
   });
 }
+inline static SmallVector<llvm::Type *, 8>
+toUnderlyingTypes(ArrayRef<LLVMType> elements) {
+  SmallVector<llvm::Type *, 8> llvmElements;
+  for (auto elt : elements)
+    llvmElements.push_back(elt.getUnderlyingType());
+  return llvmElements;
+}
+LLVMType LLVMType::createStructTy(LLVMDialect *dialect,
+                                  ArrayRef<LLVMType> elements,
+                                  Optional<StringRef> name, bool isPacked) {
+  StringRef sr = name.hasValue() ? *name : "";
+  SmallVector<llvm::Type *, 8> llvmElements(toUnderlyingTypes(elements));
+  return getLocked(dialect, [=] {
+    auto *rv = llvm::StructType::create(dialect->getLLVMContext(), sr);
+    if (!llvmElements.empty())
+      rv->setBody(llvmElements, isPacked);
+    return rv;
+  });
+}
+LLVMType LLVMType::setStructTyBody(LLVMType structType,
+                                   ArrayRef<LLVMType> elements, bool isPacked) {
+  llvm::StructType *st =
+      llvm::cast<llvm::StructType>(structType.getUnderlyingType());
+  SmallVector<llvm::Type *, 8> llvmElements(toUnderlyingTypes(elements));
+  return getLocked(&structType.getDialect(), [=] {
+    st->setBody(llvmElements, isPacked);
+    return st;
+  });
+}
 LLVMType LLVMType::getVectorTy(LLVMType elementType, unsigned numElements) {
   // Lock access to the dialect as this may modify the LLVM context.
   return getLocked(&elementType.getDialect(), [=] {

mlir/test/Dialect/LLVMIR/invalid.mlir

@@ -382,3 +382,15 @@ func @nvvm_invalid_mma_7(%a0 : !llvm<"<2 x half>">, %a1 : !llvm<"<2 x half>">,
   %0 = nvvm.mma.sync %a0, %a1, %b0, %b1, %c0, %c1, %c2, %c3, %c4, %c5, %c6, %c7 {alayout="col", blayout="row"} : (!llvm<"<2 x half>">, !llvm<"<2 x half>">, !llvm<"<2 x half>">, !llvm<"<2 x half>">, !llvm.float, !llvm.float, !llvm.float, !llvm.float, !llvm.float, !llvm.float, !llvm.float, !llvm.float) -> (!llvm<"{ float, float, float, float, float, float, float, float }">, !llvm.i32)
   llvm.return %0 : (!llvm<"{ float, float, float, float, float, float, float, float }">, !llvm.i32)
 }
+
+// -----
+
+// FIXME: the LLVM-IR dialect should parse mutually recursive types
+// CHECK-LABEL: @recursive_type
+// expected-error@+1 {{expected end of string}}
+llvm.func @recursive_type(%a : !llvm<"%a = type { %a* }">) ->
+                          !llvm<"%a = type { %a* }"> {
+  llvm.return %a : !llvm<"%a = type { %a* }">
+}
+
+