[CapturePromotion] Preserve DebugInfo when creating project_box.

The code was assigning an incorrect lexical scope, which was
responsible for an hole (and likely, wrong DI at `-Onone` in some
cases).

Fixes SR-6709.

Author: Davide Italiano

lib/SILOptimizer/IPO/CapturePromotion.cpp

@@ -1175,7 +1175,7 @@ constructClonedFunction(PartialApplyInst *PAI, FunctionRefInst *FRI,
 static SILValue getOrCreateProjectBoxHelper(SILValue PartialOperand) {
   // If we have a copy_value, just create a project_box on the copy and return.
   if (auto *CVI = dyn_cast<CopyValueInst>(PartialOperand)) {
-    SILBuilder B(std::next(CVI->getIterator()));
+    SILBuilderWithScope B(std::next(CVI->getIterator()));
     return B.createProjectBox(CVI->getLoc(), CVI, 0);
   }
 
@@ -1189,7 +1189,7 @@ static SILValue getOrCreateProjectBoxHelper(SILValue PartialOperand) {
   }
 
   // Just return a project_box.
-  SILBuilder B(std::next(Box->getIterator()));
+  SILBuilderWithScope B(std::next(Box->getIterator()));
   return B.createProjectBox(Box->getLoc(), Box, 0);
 }
 

test/SILOptimizer/sr6709.swift

@@ -0,0 +1,35 @@
+// Make sure project_box gets assigned the correct lexical scope when we create it.
+// RUN: %target-swift-frontend -primary-file %s -Onone -emit-sil -Xllvm -sil-print-after=capture-promotion -Xllvm \
+// RUN:   -sil-print-debuginfo -o /dev/null 2>&1 | %FileCheck %s
+
+// CHECK: sil hidden @_T04null19captureStackPromoteSiycyF : $@convention(thin) () -> @owned @callee_guaranteed () -> Int {
+// CHECK: bb0:
+// CHECK:   %0 = alloc_box ${ var Int }, var, name "x", loc {{.*}}:32:7, scope 3 // users: %19, %7, %1
+// CHECK:   %1 = project_box %0 : ${ var Int }, 0, loc {{.*}}:32:7, scope 3 // users: %9, %6
+// CHECK:   %2 = metatype $@thin Int.Type, loc {{.*}}:32:11, scope 3 // user: %5
+// CHECK:   %3 = integer_literal $Builtin.Int2048, 1, loc {{.*}}:32:11, scope 3 // user: %5
+// CHECK:   // function_ref Int.init(_builtinIntegerLiteral:)
+// CHECK:   %4 = function_ref @_T0Si22_builtinIntegerLiteralSiBi2048__tcfC : $@convention(method) (Builtin.Int2048, @thin Int.Type) -> Int, loc {{.*}}:32:11, scope 3 // user: %5
+// CHECK:   %5 = apply %4(%3, %2) : $@convention(method) (Builtin.Int2048, @thin Int.Type) -> Int, loc {{.*}}:32:11, scope 3 // user: %6
+// CHECK:   store %5 to [trivial] %1 : $*Int, loc {{.*}}:32:11, scope 3 // id: %6
+// CHECK:   %7 = copy_value %0 : ${ var Int }, loc {{.*}}:33:11, scope 3 // users: %12, %8
+// CHECK:   %8 = project_box %7 : ${ var Int }, 0, loc {{.*}}:33:11, scope 3 // user: %11
+// CHECK:   mark_function_escape %1 : $*Int, loc {{.*}}:33:11, scope 3 // id: %9
+// CHECK:   %10 = function_ref @_T04null19captureStackPromoteSiycyFSiycfU_Tf2i_n : $@convention(thin) (Int) -> Int, loc {{.*}}:33:11, scope 3 // user: %13
+// CHECK:   %11 = load [trivial] %8 : $*Int, loc {{.*}}:33:11, scope 3 // user: %13
+// CHECK:   destroy_value %7 : ${ var Int }, loc {{.*}}:33:11, scope 3 // id: %12
+// CHECK:   %13 = partial_apply [callee_guaranteed] %10(%11) : $@convention(thin) (Int) -> Int, loc {{.*}}:33:11, scope 3 // users: %14, %15, %17, %18
+// CHECK:   debug_value %13 : $@callee_guaranteed () -> Int, let, name "f", loc {{.*}}:33:7, scope 3 // id: %14
+// CHECK:   %15 = begin_borrow %13 : $@callee_guaranteed () -> Int, loc {{.*}}:34:10, scope 3 // users: %17, %16
+// CHECK:   %16 = copy_value %15 : $@callee_guaranteed () -> Int, loc {{.*}}:34:10, scope 3 // user: %20
+// CHECK:   end_borrow %15 from %13 : $@callee_guaranteed () -> Int, $@callee_guaranteed () -> Int, loc {{.*}}:34:10, scope 3 // id: %17
+// CHECK:   destroy_value %13 : $@callee_guaranteed () -> Int, loc {{.*}}:35:1, scope 3 // id: %18
+// CHECK:   destroy_value %0 : ${ var Int }, loc {{.*}}:35:1, scope 3 // id: %19
+// CHECK:   return %16 : $@callee_guaranteed () -> Int, loc {{.*}}:34:3, scope 3 // id: %20
+// CHECK: }
+
+func captureStackPromote() -> () -> Int {
+  var x = 1
+  let f = { x }
+  return f
+}