Optimizer: remove the obsolete SpeculativeDevirtualization pass

This pass has been disabled since a very long time (because it's terrible for code size).
It does not work for OSSA. Therefore it cannot be enabled anymore (as is) once we have OSSA throughout the pipeline.
So it's time to completely remove it.

Author: eeckstein

include/swift/AST/SILOptions.h

@@ -108,10 +108,6 @@ class SILOptions {
   /// purposes.
   bool EnableOSSAOptimizations = true;
 
-  /// Controls whether to turn on speculative devirtualization.
-  /// It is turned off by default.
-  bool EnableSpeculativeDevirtualization = false;
-
   /// Controls whether to emit actor data-race checks.
   bool EnableActorDataRaceChecks = false;
 

include/swift/Option/FrontendOptions.td

@@ -578,7 +578,7 @@ 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.">;
+  HelpText<"Deprecated, has no effect">;
 
 def enable_async_demotion : Flag<["-"], "enable-experimental-async-demotion">,
   HelpText<"Enables an optimization pass to demote async functions.">;

include/swift/SILOptimizer/PassManager/Passes.def

@@ -428,8 +428,6 @@ LEGACY_PASS(SimplifyBBArgs, "simplify-bb-args",
      "SIL Block Argument Simplification")
 LEGACY_PASS(SimplifyCFG, "simplify-cfg",
      "SIL CFG Simplification")
-LEGACY_PASS(SpeculativeDevirtualization, "specdevirt",
-     "Speculative Devirtualization via Guarded Calls")
 LEGACY_PASS(SplitAllCriticalEdges, "split-critical-edges",
      "Split all Critical Edges in the SIL CFG")
 LEGACY_PASS(SplitNonCondBrCriticalEdges, "split-non-cond_br-critical-edges",

lib/DriverTool/sil_opt_main.cpp

@@ -296,10 +296,6 @@ struct SILOptOptions {
   VerifyExclusivity = llvm::cl::opt<bool>("enable-verify-exclusivity",
                     llvm::cl::desc("Verify the access markers used to enforce exclusivity."));
 
-  llvm::cl::opt<bool>
-  EnableSpeculativeDevirtualization = llvm::cl::opt<bool>("enable-spec-devirt",
-                    llvm::cl::desc("Enable Speculative Devirtualization pass."));
-
   llvm::cl::opt<bool>
   EnableAsyncDemotion = llvm::cl::opt<bool>("enable-async-demotion",
                     llvm::cl::desc("Enables an optimization pass to demote async functions."));
@@ -891,7 +887,6 @@ int sil_opt_main(ArrayRef<const char *> argv, void *MainAddr) {
   SILOpts.EmitVerboseSIL |= options.EmitVerboseSIL;
   SILOpts.EmitSortedSIL |= options.EmitSortedSIL;
 
-  SILOpts.EnableSpeculativeDevirtualization = options.EnableSpeculativeDevirtualization;
   SILOpts.EnableAsyncDemotion = options.EnableAsyncDemotion;
   SILOpts.EnableThrowsPrediction = options.EnableThrowsPrediction;
   SILOpts.EnableNoReturnCold = options.EnableNoReturnCold;

lib/Frontend/CompilerInvocation.cpp

@@ -3081,7 +3081,6 @@ static bool ParseSILArgs(SILOptions &Opts, ArgList &Args,
   Opts.EnableOSSAOptimizations &= !Args.hasArg(OPT_disable_ossa_opts);
   Opts.EnableSILOpaqueValues = Args.hasFlag(
       OPT_enable_sil_opaque_values, OPT_disable_sil_opaque_values, false);
-  Opts.EnableSpeculativeDevirtualization |= Args.hasArg(OPT_enable_spec_devirt);
   Opts.EnableAsyncDemotion |= Args.hasArg(OPT_enable_async_demotion);
   Opts.EnableThrowsPrediction = Args.hasFlag(
       OPT_enable_throws_prediction, OPT_disable_throws_prediction,

lib/SILOptimizer/PassManager/PassPipeline.cpp

@@ -795,11 +795,6 @@ static void addClosureSpecializePassPipeline(SILPassPipelinePlan &P) {
   // Do the second stack promotion on low-level SIL.
   P.addStackPromotion();
 
-  // Speculate virtual call targets.
-  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
   // passes can expose more inlining opportunities.

lib/SILOptimizer/Transforms/CMakeLists.txt

@@ -31,6 +31,5 @@ target_sources(swiftSILOptimizer PRIVATE
   DestroyAddrHoisting.cpp
   SimplifyCFG.cpp
   Sink.cpp
-  SpeculativeDevirtualizer.cpp
   StringOptimization.cpp)