Turn off speculative devirtualization by default. (#29359)

Turn off speculative devirtualization by default. Add a flag to support enabling the pass.
Fixes rdar://58778959 and rdar://58429282

Author: meg-gupta

include/swift/AST/SILOptions.h

@@ -57,6 +57,10 @@ class SILOptions {
   /// purposes.
   bool EnableOSSAOptimizations = true;
 
+  /// Controls whether to turn on speculative devirtualization.
+  /// It is turned off by default.
+  bool EnableSpeculativeDevirtualization = false;
+
   /// Should we run any SIL performance optimizations
   ///
   /// Useful when you want to enable -O LLVM opts but not -O SIL opts.

include/swift/Option/FrontendOptions.td

@@ -282,6 +282,9 @@ def disable_ossa_opts : Flag<["-"], "disable-ossa-opts">,
 def disable_sil_partial_apply : Flag<["-"], "disable-sil-partial-apply">,
   HelpText<"Disable use of partial_apply in SIL generation">;
 
+def enable_spec_devirt : Flag<["-"], "enable-spec-devirt">,
+  HelpText<"Enable speculative devirtualization pass.">;
+
 def enable_ownership_stripping_after_serialization
   : Flag<["-"], "enable-ownership-stripping-after-serialization">,
   HelpText<"Strip ownership after serialization">;

lib/Frontend/CompilerInvocation.cpp

@@ -959,6 +959,7 @@ static bool ParseSILArgs(SILOptions &Opts, ArgList &Args,
 
   Opts.EnableARCOptimizations &= !Args.hasArg(OPT_disable_arc_opts);
   Opts.EnableOSSAOptimizations &= !Args.hasArg(OPT_disable_ossa_opts);
+  Opts.EnableSpeculativeDevirtualization |= Args.hasArg(OPT_enable_spec_devirt);
   Opts.DisableSILPerfOptimizations |= Args.hasArg(OPT_disable_sil_perf_optzns);
   Opts.CrossModuleOptimization |= Args.hasArg(OPT_CrossModuleOptimization);
   Opts.VerifyAll |= Args.hasArg(OPT_sil_verify_all);

lib/SILOptimizer/PassManager/PassPipeline.cpp

@@ -488,7 +488,9 @@ static void addClosureSpecializePassPipeline(SILPassPipelinePlan &P) {
   P.addStackPromotion();
 
   // Speculate virtual call targets.
-  P.addSpeculativeDevirtualization();
+  if (P.getOptions().EnableSpeculativeDevirtualization) {
+    P.addSpeculativeDevirtualization();
+  }
 
   // There should be at least one SILCombine+SimplifyCFG between the
   // ClosureSpecializer, etc. and the last inliner. Cleaning up after these

lib/SILOptimizer/Transforms/SpeculativeDevirtualizer.cpp

@@ -596,6 +596,7 @@ namespace {
     void run() override {
 
       auto &CurFn = *getFunction();
+
       // Don't perform speculative devirtualization at -Os.
       if (CurFn.optimizeForSize())
         return;

test/SILOptimizer/devirt_base_class.swift

@@ -1,4 +1,4 @@
-// RUN: %target-swift-frontend -O -emit-sil %s | %FileCheck %s
+// RUN: %target-swift-frontend -enable-spec-devirt -O -emit-sil %s | %FileCheck %s
 
 public class Base1 { @inline(never) func f() -> Int { return 0 } }
 

test/SILOptimizer/devirt_covariant_return.swift

@@ -1,5 +1,5 @@
 
-// RUN: %target-swift-frontend -module-name devirt_covariant_return -Xllvm -sil-full-demangle -O -Xllvm -disable-sil-cm-rr-cm=0   -Xllvm -sil-inline-generics=false -primary-file %s -emit-sil -sil-inline-threshold 1000 -Xllvm -sil-disable-pass=ObjectOutliner -sil-verify-all | %FileCheck %s
+// RUN: %target-swift-frontend -module-name devirt_covariant_return -Xllvm -sil-full-demangle -enable-spec-devirt -O -Xllvm -disable-sil-cm-rr-cm=0   -Xllvm -sil-inline-generics=false -primary-file %s -emit-sil -sil-inline-threshold 1000 -Xllvm -sil-disable-pass=ObjectOutliner -sil-verify-all | %FileCheck %s
 
 // Make sure that we can dig all the way through the class hierarchy and
 // protocol conformances with covariant return types correctly. The verifier

test/SILOptimizer/devirt_default_case.swift

@@ -1,6 +1,6 @@
 
-// RUN: %target-swift-frontend -O -module-name devirt_default_case -emit-sil %s | %FileCheck -check-prefix=CHECK -check-prefix=CHECK-NORMAL %s
-// RUN: %target-swift-frontend -O -module-name devirt_default_case -emit-sil -enable-testing %s | %FileCheck -check-prefix=CHECK -check-prefix=CHECK-TESTABLE %s
+// RUN: %target-swift-frontend -enable-spec-devirt -O -module-name devirt_default_case -emit-sil %s | %FileCheck -check-prefix=CHECK -check-prefix=CHECK-NORMAL %s
+// RUN: %target-swift-frontend -enable-spec-devirt -O -module-name devirt_default_case -emit-sil -enable-testing %s | %FileCheck -check-prefix=CHECK -check-prefix=CHECK-TESTABLE %s
 
 @_silgen_name("action")
 func action(_ n:Int) -> ()

test/SILOptimizer/devirt_protocol_method_invocations.swift

@@ -1,5 +1,5 @@
 
-// RUN: %target-swift-frontend -module-name devirt_protocol_method_invocations -O -Xllvm -sil-disable-pass=ExistentialSpecializer -emit-sil %s | %FileCheck %s
+// RUN: %target-swift-frontend -module-name devirt_protocol_method_invocations -enable-spec-devirt -O -Xllvm -sil-disable-pass=ExistentialSpecializer -emit-sil %s | %FileCheck %s
 
 protocol PPP {
     func f()

test/SILOptimizer/devirt_speculate.swift

@@ -1,4 +1,4 @@
-// RUN: %target-swift-frontend %/s -parse-as-library -O -emit-sil -save-optimization-record-path %t.opt.yaml | %FileCheck %s
+// RUN: %target-swift-frontend %/s -parse-as-library  -enable-spec-devirt -O -emit-sil -save-optimization-record-path %t.opt.yaml | %FileCheck %s
 // RUN: %FileCheck -check-prefix=YAML -input-file=%t.opt.yaml %s
 // RUN: %target-swift-frontend %/s -parse-as-library -Osize -emit-sil | %FileCheck %s --check-prefix=OSIZE
 //

test/SILOptimizer/devirt_speculative_init.swift

@@ -1,5 +1,5 @@
 
-// RUN: %target-swift-frontend %s -parse-as-library -O -emit-sil | %FileCheck %s
+// RUN: %target-swift-frontend %s -parse-as-library -enable-spec-devirt -O -emit-sil | %FileCheck %s
 // RUN: %target-swift-frontend %s -parse-as-library -Osize -emit-sil
 //
 // Test speculative devirtualization.

test/SILOptimizer/devirt_speculative_nested.swift

@@ -1,5 +1,5 @@
 
-// RUN: %target-swift-frontend -module-name devirt_speculative_nested %s -parse-as-library -O -emit-sil | %FileCheck %s
+// RUN: %target-swift-frontend -module-name devirt_speculative_nested %s -parse-as-library -enable-spec-devirt -O -emit-sil | %FileCheck %s
 // RUN: %target-swift-frontend -module-name devirt_speculative_nested %s -parse-as-library -Osize -emit-sil
 //
 // Test speculative devirtualization.

test/SILOptimizer/devirt_unbound_generic.swift

@@ -1,4 +1,4 @@
-// RUN: %target-swift-frontend -Xllvm -sil-inline-generics -emit-sorted-sil -emit-sil -O %s | %FileCheck %s
+// RUN: %target-swift-frontend -Xllvm -sil-inline-generics -emit-sorted-sil -emit-sil -enable-spec-devirt -O %s | %FileCheck %s
 
 // We used to crash on this when trying to devirtualize t.boo(a, 1),
 // because it is an "apply" with replacement types that contain

test/SILOptimizer/devirt_value_metatypes.swift

@@ -1,5 +1,5 @@
 
-// RUN: %target-swift-frontend -module-name devirt_value_metatypes -emit-sil -O %s | %FileCheck %s
+// RUN: %target-swift-frontend -module-name devirt_value_metatypes -emit-sil -enable-spec-devirt -O %s | %FileCheck %s
 
 open class A {
   @inline(never)

test/SILOptimizer/inline_cache_and_arc.swift

@@ -1,4 +1,4 @@
-// RUN: %target-swift-frontend -parse-as-library -O -emit-sil  %s | %FileCheck %s
+// RUN: %target-swift-frontend -parse-as-library -enable-spec-devirt -O -emit-sil  %s | %FileCheck %s
 // REQUIRES: swift_stdlib_no_asserts,optimized_stdlib,CPU=x86_64
 
 // Test inline cache with a global class. Make sure the retain|release pair
@@ -19,7 +19,6 @@ public func testit() {
 // CHECK-LABEL: sil @{{.*}}testityyF
 // CHECK:     bb0:
 // CHECK-NOT:   {{.*(retain|release).*}}
-// CHECK:       checked_cast_br
 // CHECK:     bb1{{.*}}:
 // CHECK-NOT:   {{.*(retain|release).*}}
 // CHECK:       return

test/SILOptimizer/opt_mode.swift

@@ -15,16 +15,6 @@ class B : A {
 
 func donothing(_ x: Int) -> Int { return x }
 
-// CHECK-LABEL: sil {{.*}} [Ospeed] @{{.*}}test_ospeed
-// CHECK: checked_cast_br
-// CHECK: checked_cast_br
-// CHECK: }
-// CHECK-IR: define hidden {{.*}}test_ospeed{{.*}} [[NOSIZE_ATTR:#[0-9]+]]
-@_optimize(speed)
-func test_ospeed(_ a: A) -> Int {
-  return donothing(a.foo(27))
-}
-
 // CHECK-LABEL: sil {{.*}} [Osize] @{{.*}}test_osize
 // CHECK: [[M:%[0-9]+]] = class_method
 // CHECK: [[A:%[0-9]+]] = apply [[M]]
@@ -46,6 +36,16 @@ func test_onone(_ a: A) -> Int {
   return donothing(a.foo(27))
 }
 
+// CHECK-LABEL: sil {{.*}} [Ospeed] @{{.*}}test_ospeed
+// CHECK: [[M:%[0-9]+]] = class_method
+// CHECK: [[A:%[0-9]+]] = apply [[M]]
+// CHECK: return [[A]]
+// CHECK-IR: define hidden {{.*}}test_ospeed{{.*}} [[NOSIZE_ATTR:#[0-9]+]]
+@_optimize(speed)
+func test_ospeed(_ a: A) -> Int {
+  return donothing(a.foo(27))
+}
+
 
-// CHECK-IR: attributes [[NOSIZE_ATTR]] = { "
 // CHECK-IR: attributes [[SIZE_ATTR]] = { minsize "
+// CHECK-IR: attributes [[NOSIZE_ATTR]] = { "

tools/sil-opt/SILOpt.cpp

@@ -102,6 +102,10 @@ static llvm::cl::opt<bool>
 VerifyExclusivity("enable-verify-exclusivity",
                   llvm::cl::desc("Verify the access markers used to enforce exclusivity."));
 
+static llvm::cl::opt<bool>
+EnableSpeculativeDevirtualization("enable-spec-devirt",
+                  llvm::cl::desc("Enable Speculative Devirtualization pass."));
+
 namespace {
 enum EnforceExclusivityMode {
   Unchecked, // static only
@@ -376,6 +380,8 @@ int main(int argc, char **argv) {
     }
   }
 
+  SILOpts.EnableSpeculativeDevirtualization = EnableSpeculativeDevirtualization;
+
   serialization::ExtendedValidationInfo extendedInfo;
   llvm::ErrorOr<std::unique_ptr<llvm::MemoryBuffer>> FileBufOrErr =
       Invocation.setUpInputForSILTool(InputFilename, ModuleName,