Guard the copy_block optimization with an experimental feature flag CopyBlockOptimization

Author: eeckstein

SwiftCompilerSources/Sources/Optimizer/InstructionSimplification/SimplifyCopyBlock.swift

@@ -28,6 +28,11 @@ extension CopyBlockInst : Simplifiable, SILCombineSimplifiable {
   /// ```
   ///
   func simplify(_ context: SimplifyContext) {
+    // Temporarily guarded with an experimental feature flag.
+    if !context.options.hasFeature(.CopyBlockOptimization) {
+      return
+    }
+
     if hasValidUses(block: self) {
       replaceBlock( self, with: operand.value, context)
       context.erase(instruction: self)

include/swift/Basic/Features.def

@@ -520,6 +520,9 @@ EXPERIMENTAL_FEATURE(ClosureBodyMacro, true)
 /// Allow declarations of Swift runtime symbols using @_silgen_name.
 EXPERIMENTAL_FEATURE(AllowRuntimeSymbolDeclarations, true)
 
+/// Optimize copies of ObjectiveC blocks.
+EXPERIMENTAL_FEATURE(CopyBlockOptimization, true)
+
 #undef EXPERIMENTAL_FEATURE_EXCLUDED_FROM_MODULE_INTERFACE
 #undef EXPERIMENTAL_FEATURE
 #undef UPCOMING_FEATURE

lib/AST/FeatureSet.cpp

@@ -429,6 +429,7 @@ UNINTERESTING_FEATURE(ImportNonPublicCxxMembers)
 UNINTERESTING_FEATURE(SuppressCXXForeignReferenceTypeInitializers)
 UNINTERESTING_FEATURE(CoroutineAccessorsUnwindOnCallerError)
 UNINTERESTING_FEATURE(AllowRuntimeSymbolDeclarations)
+UNINTERESTING_FEATURE(CopyBlockOptimization)
 
 static bool usesFeatureSwiftSettings(const Decl *decl) {
   // We just need to guard `#SwiftSettings`.

test/SILOptimizer/optimize_copy_block.swift

@@ -1,8 +1,9 @@
 // RUN: %empty-directory(%t)
 // RUN: split-file %s %t
-// RUN: %target-swift-frontend -I %t %t/test.swift -O -emit-sil | %FileCheck %s
+// RUN: %target-swift-frontend -I %t %t/test.swift -enable-experimental-feature CopyBlockOptimization -O -emit-sil | %FileCheck %s
 
 // REQUIRES: objc_interop
+// REQUIRES: swift_feature_CopyBlockOptimization
 
 //--- module.modulemap
 

test/SILOptimizer/simplify_copy_block.sil

@@ -1,6 +1,8 @@
-// RUN: %target-sil-opt %s -simplification -simplify-instruction=copy_block | %FileCheck %s
+// RUN: %target-sil-opt %s -enable-experimental-feature CopyBlockOptimization -simplification -simplify-instruction=copy_block | %FileCheck --check-prefix=CHECK --check-prefix=ENABLED %s
+// RUN: %target-sil-opt %s -simplification -simplify-instruction=copy_block | %FileCheck --check-prefix=CHECK --check-prefix=DISABLED %s
 
 // REQUIRES: objc_interop
+// REQUIRES: swift_feature_CopyBlockOptimization
 
 sil_stage canonical
 
@@ -9,9 +11,10 @@ import SwiftShims
 import Builtin
 
 // CHECK-LABEL: sil [ossa] @remove_copy_block :
-// CHECK-NOT:     copy_block
-// CHECK:         apply %0
-// CHECK-NOT:     destroy_value
+// ENABLED-NOT:     copy_block
+// ENABLED:         apply %0
+// ENABLED-NOT:     destroy_value
+// DISABLED:        copy_block
 // CHECK:       } // end sil function 'remove_copy_block'
 sil [ossa] @remove_copy_block : $@convention(thin) (@convention(block) @noescape () -> ()) -> () {
 bb0(%0 : @unowned $@convention(block) @noescape () -> ()):