[AllocBoxToStack] PAI frontier looks thru moves.

When determining where to destroy a captured alloc_box, the frontier of
the capturing partial_apply is computed.  Previously, that computation
just used the uses of the partial_apply.  If the partial_apply were
moved and the original destroyed before the apply, however, the result
would be a miscompile where the destroy_addr/dealloc_stack for the
alloc_stack to which the alloc_box was promoted was destroyed before the
apply of the closure which used the address.

Author: nate-chandler

lib/SILOptimizer/Transforms/AllocBoxToStack.cpp

@@ -1119,7 +1119,8 @@ specializeApplySite(SILOptFunctionBuilder &FuncBuilder, ApplySite Apply,
               // the alloc_stack/dealloc_stack instructions where the alloc_box/
               // destroy_value instructions are respectively.  The copy_value
               // can't keep the alloc_stack alive.
-              if ((svi = dyn_cast<CopyValueInst>(user))) {
+              if ((svi = dyn_cast<CopyValueInst>(user)) ||
+                  (svi = dyn_cast<MoveValueInst>(user))) {
                 worklist.push(svi);
               }
               users.push_back(user);

test/SILOptimizer/allocboxtostack_localapply_ossa.sil

@@ -524,3 +524,27 @@ bb0:
   %retval = tuple ()
   return %retval : $()
 }
+
+// CHECK-LABEL: sil [ossa] @test_move_applied : {{.*}} {
+// CHECK:         [[CLOSURE:%[^,]+]] = partial_apply
+// CHECK:         [[MOVE:%[^,]+]] = move_value [[CLOSURE]]
+// CHECK:         apply [[MOVE]]()
+// CHECK:         destroy_addr
+// CHECK:         dealloc_stack
+// CHECK-LABEL: } // end sil function 'test_move_applied'
+sil [ossa] @test_move_applied : $@convention(thin) () -> () {
+bb0:
+  %box = alloc_box ${ var C }, var, name "x"
+  %addr = project_box %box : ${ var C }, 0
+  %getC = function_ref @getC : $@convention(thin) () -> (@owned C)
+  %c = apply %getC() : $@convention(thin) () -> (@owned C)
+  store %c to [init] %addr : $*C
+
+  %borrow_int_box = function_ref @borrow_c_box : $@convention(thin) (@guaranteed { var C }) -> ()
+  %closure = partial_apply [callee_guaranteed] %borrow_int_box(%box) : $@convention(thin) (@guaranteed { var C }) -> ()
+  %move = move_value %closure : $@callee_guaranteed () -> ()
+  apply %move() : $@callee_guaranteed () -> ()
+  destroy_value %move : $@callee_guaranteed () -> ()
+  %retval = tuple ()
+  return %retval : $()
+}