[feature] Generalized pattern rewriting

Changes to perform generalized pattern rewriting for VP intrinsics.
This lifts InstSimplify/InstCombine and DAGCombiner patterns that were
intended for normal instructions to also work on VP intrinsics and
SDNodes.

A newer version of this is part of an RFC for LLVM: https://reviews.llvm.org/D92086

Author: Simon Moll

llvm/include/llvm/IR/MatcherCast.h

@@ -0,0 +1,67 @@
+#ifndef LLVM_IR_MATCHERCAST_H
+#define LLVM_IR_MATCHERCAST_H
+
+//===- MatcherCast.h - Match on the LLVM IR --------------------*- C++ -*-===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+//
+// Parameterized class hierachy for templatized pattern matching.
+//
+//===----------------------------------------------------------------------===//
+
+
+namespace llvm {
+namespace PatternMatch {
+
+
+// type modification
+template<typename Matcher, typename DestClass>
+struct MatcherCast {
+  using ActualCastType = DestClass;
+};
+
+// whether the Value \p Obj behaves like a \p Class.
+template<typename MatcherClass, typename Class>
+bool match_isa(const Value* Obj) {
+  using UnconstClass = typename std::remove_cv<Class>::type;
+  using DestClass = typename MatcherCast<MatcherClass, UnconstClass>::ActualCastType;
+  return isa<const DestClass>(Obj);
+}
+
+template<typename MatcherClass, typename Class>
+auto match_cast(const Value* Obj) {
+  using UnconstClass = typename std::remove_cv<Class>::type;
+  using DestClass = typename MatcherCast<MatcherClass, UnconstClass>::ActualCastType;
+  return cast<const DestClass>(Obj);
+}
+template<typename MatcherClass, typename Class>
+auto match_dyn_cast(const Value* Obj) {
+  using UnconstClass = typename std::remove_cv<Class>::type;
+  using DestClass = typename MatcherCast<MatcherClass, UnconstClass>::ActualCastType;
+  return dyn_cast<const DestClass>(Obj);
+}
+
+template<typename MatcherClass, typename Class>
+auto match_cast(Value* Obj) {
+  using UnconstClass = typename std::remove_cv<Class>::type;
+  using DestClass = typename MatcherCast<MatcherClass, UnconstClass>::ActualCastType;
+  return cast<DestClass>(Obj);
+}
+template<typename MatcherClass, typename Class>
+auto match_dyn_cast(Value* Obj) {
+  using UnconstClass = typename std::remove_cv<Class>::type;
+  using DestClass = typename MatcherCast<MatcherClass, UnconstClass>::ActualCastType;
+  return dyn_cast<DestClass>(Obj);
+}
+
+
+} // namespace PatternMatch
+
+} // namespace llvm
+
+#endif // LLVM_IR_MATCHERCAST_H
+