EscapeUtils: consider that a begin_apply can yield it's indirect arguments

This is the only apply instruction where address arguments actually can "escape"

Author: eeckstein

SwiftCompilerSources/Sources/Optimizer/Utilities/EscapeUtils.swift

@@ -547,7 +547,9 @@ fileprivate struct EscapeWalker<V: EscapeVisitor> : ValueDefUseWalker,
     }
 
     // Indirect arguments cannot escape the function, but loaded values from such can.
-    if !followLoads(at: path.projectionPath) {
+    if !followLoads(at: path.projectionPath) &&
+       // Except for begin_apply: it can yield an address value.
+       !apply.isBeginApplyWithIndirectResults {
       return .continueWalk
     }
 
@@ -824,3 +826,13 @@ private extension SmallProjectionPath {
     EscapeUtilityTypes.EscapePath(projectionPath: self, followStores: false, knownType: nil)
   }
 }
+
+private extension ApplySite {
+  var isBeginApplyWithIndirectResults: Bool {
+    guard let ba = self as? BeginApplyInst else {
+      return false
+    }
+    // Note that the token result is always a non-address type.
+    return ba.results.contains { $0.type.isAddress }
+  }
+}

test/SILOptimizer/addr_escape_info.sil

@@ -51,6 +51,7 @@ sil @initX : $@convention(method) (@owned X) -> @owned X {
 [%0: escape => %r, escape c*.v** => %r.c*.v**]
 }
 sil @modifyStr : $@convention(method) (@inout Str) -> ()
+sil @guaranteed_yield_coroutine : $@yield_once @convention(thin) (@inout X) -> @yields @inout X
 
 // CHECK-LABEL: Address escape information for test_simple:
 // CHECK:       value:  %1 = struct_element_addr %0 : $*Str, #Str.a
@@ -268,6 +269,28 @@ bb0:
   return %12 : $()
 }
 
+// CHECK-LABEL: Address escape information for indirect_argument_escape_to_yield:
+// CHECK:       value:  %1 = alloc_stack $X
+// CHECK-NEXT:    ==>   (%5, %6) = begin_apply %4(%1) : $@yield_once @convention(thin) (@inout X) -> @yields @inout X
+// CHECK-NEXT:    ==>   %8 = apply %7(%5) : $@convention(thin) (@inout X) -> ()
+// CHECK:       End function indirect_argument_escape_to_yield
+sil @indirect_argument_escape_to_yield : $@convention(thin) (@guaranteed X) -> () {
+bb0(%0 : $X):
+  %1 = alloc_stack $X
+  store %0 to %1 : $*X
+  fix_lifetime %1 : $*X
+  %3 = function_ref @guaranteed_yield_coroutine : $@yield_once @convention(thin) (@inout X) -> @yields @inout X
+  (%4, %5) = begin_apply %3(%1) : $@yield_once @convention(thin) (@inout X) -> @yields @inout X
+
+  %6 = function_ref @inout_class_argument : $@convention(thin) (@inout X) -> ()
+  %7 = apply %6(%4) : $@convention(thin) (@inout X) -> ()
+
+  end_apply %5
+  dealloc_stack %1 : $*X
+  %r = tuple ()
+  return %r : $()
+}
+
 // CHECK-LABEL: Address escape information for ignore_copy_addr_and_release:
 // CHECK:       value:  %1 = ref_element_addr %0 : $X, #X.s
 // CHECK-NEXT:    -     %6 = apply %5(%3) : $@convention(thin) (@in Str) -> ()