Summary: Introduce a new frontend flag `-fswift-async-fp={auto|always|never}` that controls how code generation sets the Swift extended async frame info bit. There are three possibilities:

[aschwaighofer]

Summary

• auto: the default, which determines how to set the bit based on

deployment target, either statically or dynamically via
swift_async_extendedFramePointerFlags.

• always: always set the bit statically, regardless of deployment

target.

• never: never set the bit, regardless of deployment target.

[doug.gregor]

Looks great, thank you!

clang/include/clang/Basic/CodeGenOptions.h

public:
   std::string BinutilsVersion;
 
   enum class FramePointerKind {
     None,        // Omit all frame pointers.
     NonLeaf,     // Keep non-leaf frame pointers.
     All,         // Keep all frame pointers.
   };
 
+  enum class SwiftAsyncFramePointerKind {
+    Auto, // Choose Swift async extended frame info based on deployment target.
+    Always, // Unconditionally emit Swift async extended frame info.
+    Never,  // Don't emit Swift async extended frame info.
+    Default = Auto,
+  };
+
   enum FiniteLoopsKind {
     Language, // Not specified, use language standard.
     Always,   // All loops are assumed to be finite.
     Never,    // No loop is assumed to be finite.
   };
 
   /// The code model to use (-mcmodel).
   std::string CodeModel;

clang/include/clang/Basic/CodeGenOptions.def

 /// according to the field declaring type width.
 CODEGENOPT(AAPCSBitfieldWidth, 1, 1)
 
 /// Sets the IEEE bit in the expected default floating point mode register.
 /// Floating point opcodes that support exception flag gathering quiet and
 /// propagate signaling NaN inputs per IEEE 754-2008 (AMDGPU Only)
 CODEGENOPT(EmitIEEENaNCompliantInsts, 1, 1)
 
+// Whether to emit Swift Async function extended frame information: auto,
+// never, always.
+ENUM_CODEGENOPT(SwiftAsyncFramePointer, SwiftAsyncFramePointerKind, 2,
+                SwiftAsyncFramePointerKind::Auto)
+
 #undef CODEGENOPT
 #undef ENUM_CODEGENOPT
 #undef VALUE_CODEGENOPT

clang/include/clang/Driver/Options.td

defm pseudo_probe_for_profiling : BoolFOption<"pseudo-probe-for-profiling",
   BothFlags<[NoXarchOption, CC1Option], " pseudo probes for sample profiling">>;
 def forder_file_instrumentation : Flag<["-"], "forder-file-instrumentation">,
     Group<f_Group>, Flags<[CC1Option, CoreOption]>,
     HelpText<"Generate instrumented code to collect order file into default.profraw file (overridden by '=' form of option or LLVM_PROFILE_FILE env var)">;
 def fprofile_list_EQ : Joined<["-"], "fprofile-list=">,
     Group<f_Group>, Flags<[CC1Option, CoreOption]>,
     HelpText<"Filename defining the list of functions/files to instrument">,
     MarshallingInfoStringVector<LangOpts<"ProfileListFiles">>;
+def fswift_async_fp_EQ : Joined<["-"], "fswift-async-fp=">,
+    Group<f_Group>, Flags<[CC1Option, CC1AsOption, CoreOption]>, MetaVarName<"<option>">,
+    HelpText<"Control emission of Swift async extended frame info (option: auto, always, never)">,
+    Values<"auto,always,never">,
+    NormalizedValuesScope<"CodeGenOptions::SwiftAsyncFramePointerKind">,
+    NormalizedValues<["Auto", "Always", "Never"]>,
+    MarshallingInfoEnum<CodeGenOpts<"SwiftAsyncFramePointer">, "Auto">;
 
 defm addrsig : BoolFOption<"addrsig",
   CodeGenOpts<"Addrsig">, DefaultFalse,
   PosFlag<SetTrue, [CC1Option], "Emit">, NegFlag<SetFalse, [], "Don't emit">,
   BothFlags<[CoreOption], " an address-significance table">>;
 defm blocks : OptInCC1FFlag<"blocks", "Enable the 'blocks' language feature", "", "", [CoreOption]>;
 def fbootclasspath_EQ : Joined<["-"], "fbootclasspath=">, Group<f_Group>;
 defm borland_extensions : BoolFOption<"borland-extensions",

clang/lib/CodeGen/BackendUtil.cpp

static bool initTargetOptions(DiagnosticsEngine &Diags,
   Options.EmitCallSiteInfo = CodeGenOpts.EmitCallSiteInfo;
   Options.EnableAIXExtendedAltivecABI = CodeGenOpts.EnableAIXExtendedAltivecABI;
   Options.PseudoProbeForProfiling = CodeGenOpts.PseudoProbeForProfiling;
   Options.ValueTrackingVariableLocations =
       CodeGenOpts.ValueTrackingVariableLocations;
   Options.XRayOmitFunctionIndex = CodeGenOpts.XRayOmitFunctionIndex;
   Options.LoopAlignment = CodeGenOpts.LoopAlignment;
 
+  switch (CodeGenOpts.getSwiftAsyncFramePointer()) {
+  case CodeGenOptions::SwiftAsyncFramePointerKind::Auto:
+    Options.SwiftAsyncFramePointer =
+        SwiftAsyncFramePointerMode::DeploymentBased;
+    break;
+
+  case CodeGenOptions::SwiftAsyncFramePointerKind::Always:
+    Options.SwiftAsyncFramePointer = SwiftAsyncFramePointerMode::Always;
+    break;
+
+  case CodeGenOptions::SwiftAsyncFramePointerKind::Never:
+    Options.SwiftAsyncFramePointer = SwiftAsyncFramePointerMode::Never;
+    break;
+  }
+
   Options.MCOptions.SplitDwarfFile = CodeGenOpts.SplitDwarfFile;
   Options.MCOptions.MCRelaxAll = CodeGenOpts.RelaxAll;
   Options.MCOptions.MCSaveTempLabels = CodeGenOpts.SaveTempLabels;
   Options.MCOptions.MCUseDwarfDirectory = !CodeGenOpts.NoDwarfDirectoryAsm;
   Options.MCOptions.MCNoExecStack = CodeGenOpts.NoExecStack;
   Options.MCOptions.MCIncrementalLinkerCompatible =
       CodeGenOpts.IncrementalLinkerCompatible;
   Options.MCOptions.MCFatalWarnings = CodeGenOpts.FatalWarnings;

clang/lib/Driver/ToolChains/Clang.cpp

   if (Args.hasFlag(options::OPT_mspeculative_load_hardening,
                    options::OPT_mno_speculative_load_hardening, false))
     CmdArgs.push_back(Args.MakeArgString("-mspeculative-load-hardening"));
 
   RenderSSPOptions(D, TC, Args, CmdArgs, KernelOrKext);
   RenderSCPOptions(TC, Args, CmdArgs);
   RenderTrivialAutoVarInitOptions(D, TC, Args, CmdArgs);
 
+  Args.AddLastArg(CmdArgs, options::OPT_fswift_async_fp_EQ);
+
   // Translate -mstackrealign
   if (Args.hasFlag(options::OPT_mstackrealign, options::OPT_mno_stackrealign,
                    false))
     CmdArgs.push_back(Args.MakeArgString("-mstackrealign"));
 
   if (Args.hasArg(options::OPT_mstack_alignment)) {
     StringRef alignment = Args.getLastArgValue(options::OPT_mstack_alignment);
     CmdArgs.push_back(Args.MakeArgString("-mstack-alignment=" + alignment));

clang/test/CodeGen/swift-async-extended-fp.c

+// RUN: %clang_cc1 -mframe-pointer=all -triple x86_64-apple-darwin10 -target-cpu core2 -S -o - %s | FileCheck %s --check-prefix=AUTO-X86
+// RUN: %clang_cc1 -mframe-pointer=all -triple x86_64-apple-darwin12 -target-cpu core2 -S -o - %s | FileCheck %s --check-prefix=ALWAYS-X86
+// RUN: %clang_cc1 -fswift-async-fp=never -mframe-pointer=all -triple x86_64-apple-darwin10 -target-cpu core2 -S -o - %s | FileCheck %s --check-prefix=NEVER-X86
+// RUN: %clang_cc1 -fswift-async-fp=never -mframe-pointer=all -triple x86_64-apple-darwin12 -target-cpu core2 -S -o - %s | FileCheck %s --check-prefix=NEVER-X86
+// RUN: %clang_cc1 -fswift-async-fp=auto -mframe-pointer=all -triple x86_64-apple-darwin10 -target-cpu core2 -S -o - %s | FileCheck %s --check-prefix=AUTO-X86
+// RUN: %clang_cc1 -fswift-async-fp=auto -mframe-pointer=all -triple x86_64-apple-darwin12 -target-cpu core2 -S -o - %s | FileCheck %s --check-prefix=ALWAYS-X86
+// RUN: %clang_cc1 -fswift-async-fp=always -mframe-pointer=all -triple x86_64-apple-darwin10 -target-cpu core2 -S -o - %s | FileCheck %s --check-prefix=ALWAYS-X86
+// RUN: %clang_cc1 -fswift-async-fp=always -mframe-pointer=all -triple x86_64-apple-darwin12 -target-cpu core2 -S -o - %s | FileCheck %s --check-prefix=ALWAYS-X86
+
+// RUN: %clang_cc1 -mframe-pointer=all -triple arm64-apple-ios9 -target-cpu cyclone -S -o - %s | FileCheck %s --check-prefix=AUTO-ARM64
+// RUN: %clang_cc1 -mframe-pointer=all -triple arm64-apple-ios15 -target-cpu cyclone -S -o - %s | FileCheck %s --check-prefix=ALWAYS-ARM64
+// RUN: %clang_cc1 -fswift-async-fp=never -mframe-pointer=all -triple arm64-apple-ios9 -target-cpu cyclone -S -o - %s | FileCheck %s --check-prefix=NEVER-ARM64
+// RUN: %clang_cc1 -fswift-async-fp=never -mframe-pointer=all -triple arm64-apple-ios15 -target-cpu cyclone -S -o - %s | FileCheck %s --check-prefix=NEVER-ARM64
+
+// REQUIRES: aarch64-registered-target,x86-registered-target
+
+#define SWIFTASYNCCALL __attribute__((swiftasynccall))
+#define ASYNC_CONTEXT __attribute__((swift_async_context))
+
+SWIFTASYNCCALL void async_context_1(ASYNC_CONTEXT void *ctx) {}
+
+// AUTO-X86: _async_context_1:
+// AUTO-X86:  _swift_async_extendedFramePointerFlags
+
+// ALWAYS-X86: _async_context_1:
+// ALWAYS-X86: btsq $60
+
+// NEVER-X86: _async_context_1:
+// NEVER-X86-NOT: _swift_async_extendedFramePointerFlags
+// NEVER-X86-NOT: btsq  $60
+
+// AUTO-ARM64: _async_context_1
+// AUTO-ARM64: _swift_async_extendedFramePointerFlags
+
+// ALWAYS-ARM64: _async_context_1
+// ALWAYS-ARM64: orr x29, x29, #0x1000000000000000
+
+// NEVER-ARM64: _async_context_1:
+// NEVER-ARM64-NOT: _swift_async_extendedFramePointerFlags
+// NEVER-ARM64-NOT: orr x29, x29, #0x1000000000000000