IRGen: Add an option to force emission of an async context pointer on the stack for leaf funclets

  `-Xfrontend -enable-async-frame-pointer-all`

rdar://135746607

Author: aschwaighofer

include/swift/AST/IRGenOptions.h

@@ -480,6 +480,10 @@ class IRGenOptions {
 
   unsigned EmitAsyncFramePushPopMetadata : 1;
 
+  // Whether to force emission of a frame for all async functions
+  // (LLVM's 'frame-pointer=all').
+  unsigned AsyncFramePointerAll : 1;
+
   /// The number of threads for multi-threaded code generation.
   unsigned NumThreads = 0;
 
@@ -570,6 +574,7 @@ class IRGenOptions {
         ColocateTypeDescriptors(true), UseRelativeProtocolWitnessTables(false),
         UseFragileResilientProtocolWitnesses(false),
         EnableHotColdSplit(false), EmitAsyncFramePushPopMetadata(false),
+        AsyncFramePointerAll(false),
         CmdArgs(), SanitizeCoverage(llvm::SanitizerCoverageOptions()),
         TypeInfoFilter(TypeInfoDumpFilter::All),
         PlatformCCallingConvention(llvm::CallingConv::C), UseCASBackend(false),

include/swift/Option/FrontendOptions.td

@@ -1324,6 +1324,13 @@ def disable_async_frame_push_pop_metadata :
   Flag<["-"], "disable-async-frame-push-pop-metadata">,
   HelpText<"Disable async frame push pop metadata">;
 
+def enable_async_frame_pointer_all :
+  Flag<["-"], "enable-async-frame-pointer-all">,
+  HelpText<"Always emit async frame stack frames (frame-pointer=all)">;
+def disable_async_frame_pointer_all:
+  Flag<["-"], "disable-async-frame-pointer-all">,
+  HelpText<"Disable always emit async frame stack frames">;
+
 def enable_split_cold_code :
   Flag<["-"], "enable-split-cold-code">,
   HelpText<"Enable splitting of cold code when optimizing">;

lib/Frontend/CompilerInvocation.cpp

@@ -3464,6 +3464,9 @@ static bool ParseIRGenArgs(IRGenOptions &Opts, ArgList &Args,
     Args.hasFlag(OPT_enable_async_frame_push_pop_metadata,
                  OPT_disable_async_frame_push_pop_metadata,
                  Opts.EmitAsyncFramePushPopMetadata);
+  Opts.AsyncFramePointerAll = Args.hasFlag(OPT_enable_async_frame_pointer_all,
+                                           OPT_disable_async_frame_pointer_all,
+                                           Opts.AsyncFramePointerAll);
   Opts.EnableLargeLoadableTypesReg2Mem =
       Args.hasFlag(OPT_enable_large_loadable_types_reg2mem,
                    OPT_disable_large_loadable_types_reg2mem,

lib/IRGen/IRGenSIL.cpp

@@ -2528,6 +2528,11 @@ void IRGenSILFunction::emitSILFunction() {
       CurFn->addFnAttr("async_entry");
       CurFn->addFnAttr(llvm::Attribute::NoInline);
     }
+
+    // For debugging purposes we always want a frame that stores the async
+    // context.
+    if (IGM.getOptions().AsyncFramePointerAll)
+      CurFn->addFnAttr("frame-pointer", "all");
   }
   if (isAsyncFn) {
     IGM.noteSwiftAsyncFunctionDef();

test/IRGen/async_frame_pointer_all.swift

@@ -0,0 +1,37 @@
+// RUN: %target-swift-frontend -primary-file %s -emit-irgen  -module-name async -disable-availability-checking -O -enable-async-frame-pointer-all | %FileCheck %s --check-prefix=ENABLED
+// RUN: %target-swift-frontend -primary-file %s -emit-irgen  -module-name async -disable-availability-checking -O -disable-async-frame-pointer-all | %FileCheck %s --check-prefix=DISABLED
+
+// x86_64 seems to choose a different default for frame pointers.
+// REQUIRES: CPU=arm64 || CPU=arm64e
+
+@inline(never)
+public func plusOne() {
+  print("+1")
+}
+
+@inline(never)
+public func minusOne() {
+  print("-1")
+}
+// ENABLED: define{{.*}} swifttailcc void @"$s5async6calleeyyYaF"(ptr swiftasync %0) [[ATTRS:#[0-9]+]]
+// ENABLED: define swifttailcc void @"$s5async6callerySiSbYaF"(ptr swiftasync %0, i1 %1) [[ATTRS]]
+
+// ENABLED: attributes [[ATTRS]] = { {{.*}}"frame-pointer"="all"
+
+// DISABLED: define{{.*}} swifttailcc void @"$s5async6calleeyyYaF"(ptr swiftasync %0) [[ATTRS:#[0-9]+]]
+// DISABLED: define swifttailcc void @"$s5async6callerySiSbYaF"(ptr swiftasync %0, i1 %1) [[ATTRS]]
+
+// DISABLED: attributes [[ATTRS]] = { {{.*}}"frame-pointer"="non-leaf"
+
+
+
+public func callee() async { }
+
+public func caller(_ b: Bool) async -> Int{
+  plusOne()
+  if b {
+    await callee()
+  }
+  minusOne()
+  return 0
+}