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

[Nikita Popov via llvm-commits]

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@@ -0,0 +1,712 @@
+//==--------------- 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)
+};
+
+template <typename MatchContext>
+using ctx_has_get_dag = decltype(std::declval<const MatchContext &>().getDAG());
+
+template <typename MatchContext>
+using ctx_has_get_tli = decltype(std::declval<const MatchContext &>().getTLI());
+
+template <typename MatchContext>
+using ctx_has_match = decltype(std::declval<const MatchContext &>().match(
+    std::declval<SDValue>(), std::declval<unsigned>()));
+
+template <typename Pattern, typename MatchContext>
+[[nodiscard]] bool sd_context_match(SDValue N, const MatchContext &Ctx,
+                                    Pattern &&P) {
+  static_assert(is_detected<ctx_has_get_dag, MatchContext>::value,
+                "Match context has to implement getDAG().");
+  static_assert(is_detected<ctx_has_get_tli, MatchContext>::value,
+                "Match context has to implement getTLI().");
+  return P.match(Ctx, N);
+}
+
+template <typename Pattern, typename MatchContext>
+[[nodiscard]] bool sd_context_match(SDNode *N, const MatchContext &Ctx,
+                                    Pattern &&P) {
+  return sd_context_match(SDValue(N, 0), Ctx, P);
+}
+
+template <typename Pattern>
+[[nodiscard]] bool sd_match(SDNode *N, const SelectionDAG *DAG, Pattern &&P) {
+  return sd_context_match(N, BasicMatchContext(DAG), P);
+}
+
+template <typename Pattern>
+[[nodiscard]] bool sd_match(SDValue N, const SelectionDAG *DAG, Pattern &&P) {
+  return sd_context_match(N, BasicMatchContext(DAG), P);
+}
+
+template <typename Pattern>
+[[nodiscard]] bool sd_match(SDNode *N, Pattern &&P) {
+  return sd_match(N, nullptr, P);
+}
+
+template <typename Pattern>
+[[nodiscard]] bool sd_match(SDValue N, Pattern &&P) {
+  return sd_match(N, nullptr, P);
+}
+
+// === Utilities ===
+struct Value_match {
+  SDValue MatchVal;
+
+  Value_match() = default;
+
+  explicit Value_match(SDValue Match) : MatchVal(Match) {}
+
+  template <typename MatchContext> bool match(const MatchContext &, SDValue N) {
+    return (MatchVal && (MatchVal == N)) || N.getNode();
----------------
nikic wrote:

I don't understand this condition. Won't this always match due to the `N.getNode()`, even if `MatchVal` is specified?

I think you should split this into separate matchers for m_Value and m_Specific.

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