[RFC][TableGen] Restructure TableGen Source (#80847)

Refactor of the llvm-tblgen source into:
- a "Basic" library, which contains the bare minimum utilities to build
`llvm-min-tablegen`
- a "Common" library which contains all of the helpers for TableGen
backends. Such helpers can be shared by more than one backend, and even
unit tested (e.g. CodeExpander is, maybe we can add more over time)

Fixes #80647

Author: Pierre-vh

llvm/unittests/TableGen/CMakeLists.txt

@@ -15,4 +15,4 @@ add_llvm_unittest(TableGenTests DISABLE_LLVM_LINK_LLVM_DYLIB
   ParserEntryPointTest.cpp
   )
 
-target_link_libraries(TableGenTests PRIVATE LLVMTableGenGlobalISel LLVMTableGen)
+target_link_libraries(TableGenTests PRIVATE LLVMTableGenCommon LLVMTableGen)

llvm/unittests/TableGen/CodeExpanderTest.cpp

@@ -6,8 +6,8 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include "GlobalISel/CodeExpander.h"
-#include "GlobalISel/CodeExpansions.h"
+#include "Common/GlobalISel/CodeExpander.h"
+#include "Common/GlobalISel/CodeExpansions.h"
 
 #include "llvm/Support/raw_ostream.h"
 #include "llvm/TableGen/Error.h"

llvm/utils/TableGen/AsmMatcherEmitter.cpp

@@ -95,12 +95,12 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include "CodeGenInstAlias.h"
-#include "CodeGenInstruction.h"
-#include "CodeGenRegisters.h"
-#include "CodeGenTarget.h"
-#include "SubtargetFeatureInfo.h"
-#include "Types.h"
+#include "Common/CodeGenInstAlias.h"
+#include "Common/CodeGenInstruction.h"
+#include "Common/CodeGenRegisters.h"
+#include "Common/CodeGenTarget.h"
+#include "Common/SubtargetFeatureInfo.h"
+#include "Common/Types.h"
 #include "llvm/ADT/CachedHashString.h"
 #include "llvm/ADT/PointerUnion.h"
 #include "llvm/ADT/STLExtras.h"

llvm/utils/TableGen/AsmWriterEmitter.cpp

@@ -11,13 +11,13 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include "AsmWriterInst.h"
-#include "CodeGenInstAlias.h"
-#include "CodeGenInstruction.h"
-#include "CodeGenRegisters.h"
-#include "CodeGenTarget.h"
-#include "SequenceToOffsetTable.h"
-#include "Types.h"
+#include "Basic/SequenceToOffsetTable.h"
+#include "Common/AsmWriterInst.h"
+#include "Common/CodeGenInstAlias.h"
+#include "Common/CodeGenInstruction.h"
+#include "Common/CodeGenRegisters.h"
+#include "Common/CodeGenTarget.h"
+#include "Common/Types.h"
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/DenseMap.h"
 #include "llvm/ADT/STLExtras.h"

llvm/utils/TableGen/Basic/CMakeLists.txt

@@ -0,0 +1,21 @@
+# The basic TableGen library contains as little dependencies as possible.
+# In particular, it does not depend on vt_gen -> it does not use ValueTypes.
+#
+# This library is the only thing included in `llvm-min-tablegen`.
+
+set(LLVM_LINK_COMPONENTS
+  Support
+  TableGen
+  )
+
+add_llvm_library(LLVMTableGenBasic STATIC OBJECT EXCLUDE_FROM_ALL
+  CodeGenIntrinsics.cpp
+  SDNodeProperties.cpp
+)
+set_target_properties(LLVMTableGenBasic PROPERTIES FOLDER "Tablegenning")
+
+# Users may include its headers as "Basic/*.h"
+target_include_directories(LLVMTableGenBasic
+  INTERFACE
+  $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/..>
+  )