Expose function sections option (#28088)

* Expose separate function sections option to compiler

* Add function sections test

include/swift/AST/IRGenOptions.h

@@ -146,6 +146,9 @@ public:
   /// objects.
   unsigned EmitStackPromotionChecks : 1;
 
+  /// Emit functions to separate sections.
+  unsigned FunctionSections : 1;
+
   /// The maximum number of bytes used on a stack frame for stack promotion
   /// (includes alloc_stack allocations).
   unsigned StackPromotionSizeLimit = 1024;
@@ -253,7 +256,7 @@ public:
         IntegratedREPL(false), DisableLLVMOptzns(false),
         DisableSwiftSpecificLLVMOptzns(false), DisableLLVMSLPVectorizer(false),
         DisableFPElim(true), Playground(false), EmitStackPromotionChecks(false),
-        PrintInlineTree(false), EmbedMode(IRGenEmbedMode::None),
+        FunctionSections(false), PrintInlineTree(false), EmbedMode(IRGenEmbedMode::None),
         HasValueNamesSetting(false), ValueNames(false),
         EnableReflectionMetadata(true), EnableReflectionNames(true),
         EnableAnonymousContextMangledNames(false), ForcePublicLinkage(false),

include/swift/Option/FrontendOptions.td

@@ -334,6 +334,10 @@ def disable_reflection_names : Flag<["-"], "disable-reflection-names">,
   HelpText<"Disable emission of names of stored properties and enum cases in"
            "reflection metadata">;
 
+def function_sections: Flag<["-"], "function-sections">,
+  Flags<[FrontendOption, NoInteractiveOption]>,
+  HelpText<"Emit functions to separate sections.">;
+
 def stack_promotion_checks : Flag<["-"], "emit-stack-promotion-checks">,
   HelpText<"Emit runtime checks for correct stack promotion of objects.">;
 

lib/Frontend/CompilerInvocation.cpp

@@ -1136,6 +1136,8 @@ static bool ParseIRGenArgs(IRGenOptions &Opts, ArgList &Args,
     Opts.StackPromotionSizeLimit = limit;
   }
 
+  Opts.FunctionSections = Args.hasArg(OPT_function_sections);
+
   if (Args.hasArg(OPT_autolink_force_load))
     Opts.ForceLoadSymbolName = Args.getLastArgValue(OPT_module_link_name);
 

lib/IRGen/IRGen.cpp

@@ -162,6 +162,7 @@ swift::getIRTargetOptions(IRGenOptions &Opts, ASTContext &Ctx) {
   // Explicitly request debugger tuning for LLDB which is the default
   // on Darwin platforms but not on others.
   TargetOpts.DebuggerTuning = llvm::DebuggerKind::LLDB;
+  TargetOpts.FunctionSections = Opts.FunctionSections;
 
   auto *Clang = static_cast<ClangImporter *>(Ctx.getClangModuleLoader());
   clang::TargetOptions &ClangOpts = Clang->getTargetInfo().getTargetOpts();

test/LinkerSections/Inputs/FunctionSections.swift

@@ -0,0 +1,5 @@
+public typealias Void = ()
+
+public func func1() -> Void {}
+
+public func func2() -> Void {}

test/LinkerSections/Inputs/FunctionSectionsUse.swift

@@ -0,0 +1,3 @@
+import FunctionSections
+
+func1()

test/LinkerSections/function_sections.swift

@@ -0,0 +1,10 @@
+// REQUIRES: OS=linux-gnu || OS=linux-androideabi || OS=linux-android || OS=freebsd
+// RUN: %empty-directory(%t)
+// RUN: %target-build-swift -Xfrontend -function-sections -emit-module -emit-library -static -parse-stdlib %S/Inputs/FunctionSections.swift
+// RUN: %target-build-swift -Xlinker --gc-sections -Xlinker -Map=%t/../../FunctionSections.map -I%t/../.. -L%t/../.. -lFunctionSections %S/Inputs/FunctionSectionsUse.swift
+// RUN: %FileCheck %s < %t/../../FunctionSections.map
+
+// CHECK: Discarded input sections
+// CHECK: .text.$s16FunctionSections5func2yyF
+// CHECK: Memory map
+// CHECK: .text.$s16FunctionSections5func1yyF

test/LinkerSections/function_sections_ir_check.swift

@@ -0,0 +1,12 @@
+// RUN: %empty-directory(%t)
+// RUN: %target-build-swift -Xfrontend -function-sections -emit-library -emit-ir -static -parse-stdlib %S/Inputs/FunctionSections.swift | %FileCheck %s
+
+// CHECK: define {{(dllexport |protected )?}}swiftcc void @"$s16FunctionSections5func1yyF"() #0 {
+// CHECK: entry:
+// CHECK:   ret void
+// CHECK: }
+
+// CHECK: define {{(dllexport |protected )?}}swiftcc void @"$s16FunctionSections5func2yyF"() #0 {
+// CHECK: entry:
+// CHECK:   ret void
+// CHECK: }