1 files changed, 42 insertions, 3 deletions
diff --git a/llvm/lib/CodeGen/LiveDebugValues/InstrRefBasedImpl.h b/llvm/lib/CodeGen/LiveDebugValues/InstrRefBasedImpl.h
index d6dbb1feda3e..ccc284b62331 100644
--- a/llvm/lib/CodeGen/LiveDebugValues/InstrRefBasedImpl.h
+++ b/llvm/lib/CodeGen/LiveDebugValues/InstrRefBasedImpl.h
@@ -207,9 +207,48 @@ using namespace llvm;
 /// Type for a table of values in a block.
 using ValueTable = SmallVector<ValueIDNum, 0>;
 
-/// Type for a table-of-table-of-values, i.e., the collection of either
-/// live-in or live-out values for each block in the function.
-using FuncValueTable = SmallVector<ValueTable, 0>;
+/// A collection of ValueTables, one per BB in a function, with convenient
+/// accessor methods.
+struct FuncValueTable {
+  FuncValueTable(int NumBBs, int NumLocs) {
+    Storage.reserve(NumBBs);
+    for (int i = 0; i != NumBBs; ++i)
+      Storage.push_back(
+          std::make_unique<ValueTable>(NumLocs, ValueIDNum::EmptyValue));
+  }
+
+  /// Returns the ValueTable associated with MBB.
+  ValueTable &operator[](const MachineBasicBlock &MBB) const {
+    return (*this)[MBB.getNumber()];
+  }
+
+  /// Returns the ValueTable associated with the MachineBasicBlock whose number
+  /// is MBBNum.
+  ValueTable &operator[](int MBBNum) const {
+    auto &TablePtr = Storage[MBBNum];
+    assert(TablePtr && "Trying to access a deleted table");
+    return *TablePtr;
+  }
+
+  /// Returns the ValueTable associated with the entry MachineBasicBlock.
+  ValueTable &tableForEntryMBB() const { return (*this)[0]; }
+
+  /// Returns true if the ValueTable associated with MBB has not been freed.
+  bool hasTableFor(MachineBasicBlock &MBB) const {
+    return Storage[MBB.getNumber()] != nullptr;
+  }
+
+  /// Frees the memory of the ValueTable associated with MBB.
+  void ejectTableForBlock(const MachineBasicBlock &MBB) {
+    Storage[MBB.getNumber()].reset();
+  }
+
+private:
+  /// ValueTables are stored as unique_ptrs to allow for deallocation during
+  /// LDV; this was measured to have a significant impact on compiler memory
+  /// usage.
+  SmallVector<std::unique_ptr<ValueTable>, 0> Storage;
+};
 
 /// Thin wrapper around an integer -- designed to give more type safety to
 /// spill location numbers.