[NFC][TableGen][GlobalISel] Move MIR pattern parsing out of combiner (#86789)

Reland of cfa0833

Author: Pierre-vh

llvm/utils/TableGen/Common/CMakeLists.txt

@@ -12,10 +12,12 @@ set(LLVM_LINK_COMPONENTS
 
 add_llvm_library(LLVMTableGenCommon STATIC OBJECT EXCLUDE_FROM_ALL
   GlobalISel/CodeExpander.cpp
+  GlobalISel/CombinerUtils.cpp
   GlobalISel/CXXPredicates.cpp
   GlobalISel/GlobalISelMatchTable.cpp
   GlobalISel/GlobalISelMatchTableExecutorEmitter.cpp
   GlobalISel/MatchDataInfo.cpp
+  GlobalISel/PatternParser.cpp
   GlobalISel/Patterns.cpp
 
   AsmWriterInst.cpp

llvm/utils/TableGen/Common/GlobalISel/CombinerUtils.cpp

@@ -0,0 +1,23 @@
+//===- CombinerUtils.cpp --------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "CombinerUtils.h"
+#include "llvm/ADT/StringSet.h"
+
+namespace llvm {
+
+StringRef insertStrRef(StringRef S) {
+  if (S.empty())
+    return {};
+
+  static StringSet<> Pool;
+  auto [It, Inserted] = Pool.insert(S);
+  return It->getKey();
+}
+
+} // namespace llvm

llvm/utils/TableGen/Common/GlobalISel/CombinerUtils.h

@@ -65,6 +65,10 @@ inline const DagInit *getDagWithOperatorOfSubClass(const Init &N,
         return I;
   return nullptr;
 }
+
+/// Copies a StringRef into a static pool to preserve it.
+StringRef insertStrRef(StringRef S);
+
 } // namespace llvm
 
 #endif