Fix SILCombine of MarkDependenceInst.

Do not eliminate a mark_dependence on a begin_apply scope even though the token
has a trivial type.

Ideally, token would have a non-trivial Builtin type to avoid special cases.

(only relevant on 6.2)

Author: atrick

lib/SILOptimizer/SILCombiner/SILCombinerMiscVisitors.cpp

@@ -1699,11 +1699,16 @@ static SILInstruction *combineMarkDependenceBaseInst(
   {
     SILType baseType = mdi->getBase()->getType();
     if (baseType.getObjectType().isTrivial(*mdi->getFunction())) {
-      if (auto mdValue = dyn_cast<MarkDependenceInst>(mdi)) {
-        auto &valOper = mdi->getAllOperands()[MarkDependenceInst::Dependent];
-        mdValue->replaceAllUsesWith(valOper.get());
+      // begin_apply is a special case. A dependency on the token is limited
+      // to the coroutine scope (ideally, the token
+      // would have a non-trivial type like $Builtin.Token).
+      if (!isa_and_nonnull<BeginApplyInst>(mdi->getBase()->getDefiningInstruction())) {
+        if (auto mdValue = dyn_cast<MarkDependenceInst>(mdi)) {
+          auto &valOper = mdi->getAllOperands()[MarkDependenceInst::Dependent];
+          mdValue->replaceAllUsesWith(valOper.get());
+        }
+        return C->eraseInstFromFunction(*mdi);
       }
-      return C->eraseInstFromFunction(*mdi);
     }
   }
   return nullptr;

test/SILOptimizer/sil_combine_apply.sil

@@ -1,6 +1,7 @@
-// RUN: %target-sil-opt -sil-print-types -enable-sil-verify-all %s -sil-combine -sil-combine-disable-alloc-stack-opts | %FileCheck %s
+// RUN: %target-sil-opt -sil-print-types -enable-sil-verify-all %s -sil-combine -sil-combine-disable-alloc-stack-opts -enable-experimental-feature Lifetimes | %FileCheck %s
 
 // REQUIRES: swift_in_compiler
+// REQUIRES: swift_feature_Lifetimes
 
 import Swift
 import Builtin
@@ -27,6 +28,18 @@ protocol FakeProtocol {
   func requirement()
 }
 
+struct NE: ~Escapable {}
+
+struct NEHolder : ~Escapable {
+  var ne: NE {
+    @_lifetime(borrow self)
+    get
+  }
+}
+
+sil @read_ne : $@yield_once @convention(method) (@guaranteed NEHolder) -> @lifetime(borrow 0) @yields @guaranteed NE
+sil @use_ne : $@convention(thin) (@guaranteed NE) -> ()
+
 /////////////////////////////////
 // Tests for SILCombinerApply. //
 /////////////////////////////////
@@ -1019,3 +1032,27 @@ bb3:
   %rv = tuple()
   return %rv : $()
 }
+
+// CHECK-LABEL: sil hidden [ossa] @testChainedDependence : $@convention(thin) (@guaranteed NEHolder) -> () {
+// CHECK: bb0(%0 : @noImplicitCopy @guaranteed $NEHolder):
+// CHECK:   ([[YIELD:%[0-9]+]], [[TOKEN:%[0-9]+]]) = begin_apply %{{.*}}(%{{.*}}) : $@yield_once @convention(method) (@guaranteed NEHolder) -> @lifetime(borrow 0) @yields @guaranteed NE
+// CHECK:   [[MD1:%[0-9]+]] = mark_dependence [nonescaping] [[YIELD]] : $NE on [[TOKEN]]
+// CHECK:   mark_dependence [nonescaping] [[MD1]]
+// CHECK-LABEL: } // end sil function 'testChainedDependence'
+sil hidden [ossa] @testChainedDependence : $@convention(thin) (@guaranteed NEHolder) -> () {
+bb0(%0 : @noImplicitCopy @guaranteed $NEHolder):
+  %2 = begin_borrow %0
+  %3 = function_ref @read_ne : $@yield_once @convention(method) (@guaranteed NEHolder) -> @lifetime(borrow 0) @yields @guaranteed NE
+  (%4, %5) = begin_apply %3(%2) : $@yield_once @convention(method) (@guaranteed NEHolder) -> @lifetime(borrow 0) @yields @guaranteed NE
+  %6 = mark_dependence [nonescaping] %4 on %5
+  %7 = mark_dependence [nonescaping] %6 on %2
+  %8 = copy_value %7
+  %9 = move_value [var_decl] %8
+  %11 = function_ref @use_ne : $@convention(thin) (@guaranteed NE) -> ()
+  %12 = apply %11(%9) : $@convention(thin) (@guaranteed NE) -> ()
+  destroy_value %9
+  %14 = end_apply %5 as $()
+  end_borrow %2
+  %16 = tuple ()
+  return %16
+}