[SILOptimizer] Stop optimization after serialization if only emitting a module

include/swift/AST/SILOptions.h

@@ -70,6 +70,9 @@ class SILOptions {
   /// Whether to dump verbose SIL with scope and location information.
   bool EmitVerboseSIL = false;
 
+  /// Whether to stop the optimization pipeline after serializing SIL.
+  bool StopOptimizationAfterSerialization = false;
+
   /// Optimization mode being used.
   OptimizationMode OptMode = OptimizationMode::NotSet;
 

lib/Frontend/CompilerInvocation.cpp

@@ -655,6 +655,11 @@ static bool ParseSILArgs(SILOptions &Opts, ArgList &Args,
     }
   }
 
+  // If we're only emitting a module, stop optimizations once we've serialized
+  // the SIL for the module.
+  if (FEOpts.RequestedAction == FrontendOptions::ActionType::EmitModuleOnly)
+    Opts.StopOptimizationAfterSerialization = true;
+
   if (Args.hasArg(OPT_sil_merge_partial_modules))
     Opts.MergePartialModules = true;
 

lib/SILOptimizer/PassManager/PassPipeline.cpp

@@ -225,7 +225,8 @@ void addHighLevelLoopOptPasses(SILPassPipelinePlan &P) {
 }
 
 // Perform classic SSA optimizations.
-void addSSAPasses(SILPassPipelinePlan &P, OptimizationLevelKind OpLevel) {
+void addSSAPasses(SILPassPipelinePlan &P, OptimizationLevelKind OpLevel,
+                  bool stopAfterSerialization = false) {
   // Promote box allocations to stack allocations.
   P.addAllocBoxToStack();
 
@@ -282,6 +283,9 @@ void addSSAPasses(SILPassPipelinePlan &P, OptimizationLevelKind OpLevel) {
     // which reduces the ability of the compiler to optimize clients
     // importing this module.
     P.addSerializeSILPass();
+    if (stopAfterSerialization)
+      return;
+
     // Does inline semantics-functions (except "availability"), but not
     // global-init functions.
     P.addPerfInliner();
@@ -384,9 +388,12 @@ static void addMidModulePassesStackPromotePassPipeline(SILPassPipelinePlan &P) {
   P.addStackPromotion();
 }
 
-static void addMidLevelPassPipeline(SILPassPipelinePlan &P) {
+static bool addMidLevelPassPipeline(SILPassPipelinePlan &P,
+                                    bool stopAfterSerialization) {
   P.startPipeline("MidLevel");
-  addSSAPasses(P, OptimizationLevelKind::MidLevel);
+  addSSAPasses(P, OptimizationLevelKind::MidLevel, stopAfterSerialization);
+  if (stopAfterSerialization)
+    return true;
 
   // Specialize partially applied functions with dead arguments as a preparation
   // for CapturePropagation.
@@ -395,6 +402,7 @@ static void addMidLevelPassPipeline(SILPassPipelinePlan &P) {
   // Run loop unrolling after inlining and constant propagation, because loop
   // trip counts may have became constant.
   P.addLoopUnroll();
+  return false;
 }
 
 static void addClosureSpecializePassPipeline(SILPassPipelinePlan &P) {
@@ -574,7 +582,8 @@ SILPassPipelinePlan::getPerformancePassPipeline(const SILOptions &Options) {
   addMidModulePassesStackPromotePassPipeline(P);
 
   // Run an iteration of the mid-level SSA passes.
-  addMidLevelPassPipeline(P);
+  if (addMidLevelPassPipeline(P, Options.StopOptimizationAfterSerialization))
+    return P;
 
   // Perform optimizations that specialize.
   addClosureSpecializePassPipeline(P);

test/SILOptimizer/stop_after_module.swift

@@ -0,0 +1,23 @@
+// RUN: %target-swift-frontend -c -o /dev/null -O -Xllvm -sil-print-after=inline %s 2>&1 | %FileCheck %s --check-prefix NOTSKIPPING
+// RUN: %target-swift-frontend -emit-sil -o /dev/null -O -Xllvm -sil-print-after=inline %s 2>&1 | %FileCheck %s --check-prefix NOTSKIPPING
+// RUN: %target-swift-frontend -emit-module -o /dev/null -O -Xllvm -sil-print-after=inline %s 2>&1 | %FileCheck %s --check-prefix SKIPPING
+
+// This test ensures that we don't run the Perf Inliner after serializing a
+// module, if we're stopping optimizations after serializing. We want to also
+// make sure we _do_ still run the Perf Inliner when we're doing a full
+// compile or emitting SIL directly.
+
+@inline(never)
+func _blackHole(_ x: Int) {}
+
+@inlinable
+public func inlinableFunction(_ x: Int) -> Int {
+  return x + 1
+}
+
+public func caller() {
+  _blackHole(inlinableFunction(20))
+}
+
+// NOTSKIPPING: *** SIL function after {{.*}}, stage MidLevel, pass {{.*}}: PerfInliner (inline)
+// SKIPPING-NOT: *** SIL function after {{.*}}, stage MidLevel, pass {{.*}}: PerfInliner (inline)