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

[via llvm-commits]

================
@@ -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,
----------------
vporpo wrote:

The interval describes a range of nodes in program order. This particular interval is going to be used as the range of nodes to be scanned for dependencies as we are building the DAG. The DAG's interval is the range of instructions that are represented by the DAG, it's only used to check if some instruction/node is inside or outside the DAG.

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