Update SwiftCompilerSources AllocBoxToStack to handle mark_dep.

Handle the easy case in which the promoted box is the base operand of a
mark_dep. This requires nothing more than setting the base operand to the new
stack address.

Required for move-only checking. Otherwise, we get an incredibly bizarre
compiler error: noncopyable 'foo' cannot be consumed when captured by an
escaping closure

The legacy pass was updated first for 6.2.

Author: atrick

SwiftCompilerSources/Sources/Optimizer/FunctionPasses/AllocBoxToStack.swift

@@ -154,6 +154,12 @@ private func canPromote(allocBox: AllocBoxInst) -> (promotableArguments: [Functi
         fallthrough
       case is MarkUninitializedInst, is CopyValueInst, is MoveValueInst:
         worklist.pushIfNotVisited(use.instruction as! SingleValueInstruction)
+      case let markDep as MarkDependenceInstruction:
+        if markDep.baseOperand == use {
+          // mark_dependence base value uses will be directly converted to base address uses.
+          break
+        }
+        return nil
       case let apply as ApplySite:
         if apply.isCallee(operand: use) {
           // Calling the closure does not escape the closure value.
@@ -226,6 +232,9 @@ private struct FunctionSpecializations {
         // First, replace the instruction with the original `box`, which adds more uses to `box`.
         // In a later iteration those additional uses will be handled.
         (user as! SingleValueInstruction).replace(with: box, context)
+      case let markDep as MarkDependenceInstruction:
+        assert(markDep.baseOperand == use)
+        markDep.baseOperand.set(to: stack, context)
       case let apply as ApplySite:
         specialize(apply: apply, context)
       default:

test/SILOptimizer/allocbox_to_stack_ne.sil

@@ -1,4 +1,5 @@
 // RUN: %target-sil-opt -enable-experimental-feature LifetimeDependence -allocbox-to-stack %s | %FileCheck %s
+// RUN: %target-sil-opt -enable-experimental-feature LifetimeDependence -legacy-allocbox-to-stack %s | %FileCheck %s
 
 // REQUIRES: swift_feature_LifetimeDependence