[llvm] [SandboxVec][DAG] MemDGNode for memory-dependency candidate nodes (PR #109684)

[Alina Sbirlea via llvm-commits]

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@@ -66,9 +88,46 @@ class DGNode {
 #endif // NDEBUG
 };
 
+/// A DependencyGraph Node for instructions that may read/write memory, or have
+/// some ordering constraints, like with stacksave/stackrestore and
+/// alloca/inalloca.
+class MemDGNode final : public DGNode {
+  MemDGNode *PrevMemN = nullptr;
+  MemDGNode *NextMemN = nullptr;
+
+  void setNextNode(MemDGNode *N) { NextMemN = N; }
+  void setPrevNode(MemDGNode *N) { PrevMemN = N; }
+  friend class DependencyGraph; // For setNextNode(), setPrevNode().
+
+public:
+  MemDGNode(Instruction *I) : DGNode(I, DGNodeID::MemDGNode) {
+    assert(isMemDepCandidate(I) && "Expected Mem instruction!");
+  }
+  static bool classof(const DGNode *Other) {
+    return Other->SubclassID == DGNodeID::MemDGNode;
+  }
+  /// \Returns the previous Mem DGNode in instruction order.
+  MemDGNode *getPrevNode() const { return PrevMemN; }
+  /// \Returns the next Mem DGNode in instruction order.
+  MemDGNode *getNextNode() const { return NextMemN; }
+};
+
+/// Convenience builders for a MemDGNode interval.
+class MemDGNodeIntervalBuilder {
+public:
+  /// Given \p Instrs it finds their closest mem nodes in the interval and
+  /// returns the corresponding mem range. Note: BotN (or its neighboring mem
+  /// node) is included in the range.
+  static Interval<MemDGNode> make(const Interval<Instruction> &Instrs,
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alinas wrote:

Can you elaborate why you need both Interval<Instructions> and a DAG? The DAG has an interval<Instruction> inside. Are they different intervals, what's the usage for each?

https://github.com/llvm/llvm-project/pull/109684