Swift optimizer: add Value.makeAvailable and `Value.copy(at:andMakeAvailableIn:)

Utilities to make a value available to be used in another basic block.
Inserts required `copy_value` and `destroy_value` operations in case the destination block is in a different control region than the value.
For example, if the destination block is in a loop while the value is not in that loop, the value has to be copied for each loop iteration.

Author: eeckstein

SwiftCompilerSources/Sources/Optimizer/Utilities/OptUtils.swift

@@ -35,3 +35,45 @@ extension Builder {
     }
   }
 }
+
+extension Value {
+  /// Makes this new owned value available to be used in the block `destBlock`.
+  ///
+  /// Inserts required `copy_value` and `destroy_value` operations in case the `destBlock`
+  /// is in a different control region than this value. For example, if `destBlock` is
+  /// in a loop while this value is not in that loop, the value has to be copied for
+  /// each loop iteration.
+  func makeAvailable(in destBlock: BasicBlock, _ context: PassContext) -> Value {
+    precondition(uses.isEmpty)
+    precondition(ownership == .owned)
+
+    let beginBlock = definingBlock
+    var useToDefRange = BasicBlockRange(begin: beginBlock, context)
+    defer { useToDefRange.deinitialize() }
+
+    useToDefRange.insert(destBlock)
+
+    // The value needs to be destroyed at every exit of the liferange.
+    for exitBlock in useToDefRange.exits {
+      let builder = Builder(at: exitBlock.instructions.first!, context)
+      builder.createDestroyValue(operand: self)
+    }
+  
+    if useToDefRange.contains(destBlock) {
+      // The `destBlock` is within a loop, so we need to copy the value at each iteration.
+      let builder = Builder(at: destBlock.instructions.first!, context)
+      return builder.createCopyValue(operand: self)
+    }
+    return self
+  }
+
+  /// Copies this value at `insertionPoint` and makes the copy available to be used in `destBlock`.
+  ///
+  /// For details see `makeAvailable`.
+  func copy(at insertionPoint: Instruction, andMakeAvailableIn destBlock: BasicBlock,
+            _ context: PassContext) -> Value {
+    let builder = Builder(at: insertionPoint, context)
+    let copiedValue = builder.createCopyValue(operand: self)
+    return copiedValue.makeAvailable(in: destBlock, context)
+  }
+}