[llvm] [SelectionDAG] Introducing the SelectionDAG pattern matching framework (PR #78654)

[Min-Yih Hsu via llvm-commits]

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+//==--------------- llvm/CodeGen/SDPatternMatch.h ---------------*- 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
+//
+//===----------------------------------------------------------------------===//
+/// \file
+/// Contains matchers for matching SelectionDAG nodes and values.
+///
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CODEGEN_SDPATTERNMATCH_H
+#define LLVM_CODEGEN_SDPATTERNMATCH_H
+
+#include "llvm/ADT/APInt.h"
+#include "llvm/ADT/STLExtras.h"
+#include "llvm/CodeGen/SelectionDAG.h"
+#include "llvm/CodeGen/SelectionDAGNodes.h"
+#include "llvm/CodeGen/TargetLowering.h"
+
+namespace llvm {
+namespace SDPatternMatch {
+
+/// MatchContext can repurpose existing patterns to behave differently under
+/// a certain context. For instance, `m_Opc(ISD::ADD)` matches plain ADD nodes
+/// in normal circumstances, but matches VP_ADD nodes under a custom
+/// VPMatchContext. This design is meant to facilitate code / pattern reusing.
+class BasicMatchContext {
+  const SelectionDAG *DAG;
+  const TargetLowering *TLI;
+
+public:
+  explicit BasicMatchContext(const SelectionDAG *DAG)
+      : DAG(DAG), TLI(DAG ? &DAG->getTargetLoweringInfo() : nullptr) {}
+
+  explicit BasicMatchContext(const TargetLowering *TLI)
+      : DAG(nullptr), TLI(TLI) {}
+
+  // A valid MatchContext has to implement the following functions.
+
+  const SelectionDAG *getDAG() const { return DAG; }
+
+  const TargetLowering *getTLI() const {
+    if (TLI)
+      return TLI;
+    return DAG ? &DAG->getTargetLoweringInfo() : nullptr;
+  }
+
+  // Optional trait function(s)
+
+  /// Return true if N effectively has opcode Opcode.
+  // bool match(SDValue N, unsigned Opcode)
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mshockwave wrote:

> Do we expect there to be more contexts than BaseContext and VPMatchContext? I don't think that custom context will be common enough that we have to optimize for implementing one method less.

I'm convinced, I'll change this in the next update.

https://github.com/llvm/llvm-project/pull/78654