TempRValueOptimization: don't optimize copies to mark_dependence base values.

We want to keep the original lifetime of the base. If we would eliminate the base alloc_stack, we risk to insert a destroy_addr too early.

Author: eeckstein

lib/SILOptimizer/Transforms/TempRValueElimination.cpp

@@ -181,10 +181,10 @@ collectLoads(Operand *addressUse, CopyAddrInst *originalCopy,
   }
   case SILInstructionKind::MarkDependenceInst: {
     auto mdi = cast<MarkDependenceInst>(user);
-    // If the user is the base operand of the MarkDependenceInst we can return
-    // true, because this would be the end of this dataflow chain
     if (mdi->getBase() == address) {
-      return true;
+      // We want to keep the original lifetime of the base. If we would eliminate
+      // the base alloc_stack, we risk to insert a destroy_addr too early.
+      return false;
     }
     // If the user is the value operand of the MarkDependenceInst we have to
     // transitively explore its uses until we reach a load or return false

test/SILOptimizer/temp_rvalue_opt.sil

@@ -34,6 +34,8 @@ sil @unknown : $@convention(thin) () -> ()
 sil @load_string : $@convention(thin) (@in_guaranteed String) -> String
 sil @guaranteed_user : $@convention(thin) (@guaranteed Klass) -> ()
 sil @consume : $@convention(thin) (@owned C) -> ()
+sil @createKlass : $@convention(thin) () -> @owned Klass
+sil @initC : $@convention(thin) () -> @out C
 
 sil @inguaranteed_user_without_result : $@convention(thin) (@in_guaranteed Klass) -> () {
 bb0(%0 : $*Klass):
@@ -802,3 +804,26 @@ bb0(%0 : $C):
   dealloc_stack %2
   return %5
 }
+
+// CHECK-LABEL: sil [ossa] @dont_shrink_lifetime_of_mark_dependence_base
+// CHECK:         copy_addr
+// CHECK:         apply
+// CHECK:       } // end sil function 'dont_shrink_lifetime_of_mark_dependence_base'
+sil [ossa] @dont_shrink_lifetime_of_mark_dependence_base : $@convention(thin) () -> () {
+bb0:
+  %0 = alloc_stack $C
+  %1 = function_ref @initC : $@convention(thin) () -> @out C
+  %2 = apply %1(%0) : $@convention(thin) () -> @out C
+  %3 = alloc_stack [var_decl] $C, let, name "a"
+  copy_addr [take] %0 to [init] %3
+  %5 = function_ref @createKlass : $@convention(thin) () -> @owned Klass
+  %6 = apply %5() : $@convention(thin) () -> @owned Klass
+  %7 = mark_dependence [nonescaping] %6 on %3
+  destroy_value %7
+  destroy_addr %3
+  dealloc_stack %3
+  dealloc_stack %0
+  %12 = tuple ()
+  return %12
+}
+