Teach the backend to make references to swift_async_extendedFramePointerFlags weak if it emits it

When references to the symbol `swift_async_extendedFramePointerFlags`
are emitted they have to be weak.

References to the symbol `swift_async_extendedFramePointerFlags` get
emitted only by frame lowering code. Therefore, the backend needs to track
references to the symbol and mark them weak.

Differential Revision: https://reviews.llvm.org/D115672

llvm/include/llvm/CodeGen/AsmPrinter.h

@@ -799,6 +799,11 @@ private:
 
   /// This method decides whether the specified basic block requires a label.
   bool shouldEmitLabelForBasicBlock(const MachineBasicBlock &MBB) const;
+
+protected:
+  virtual bool shouldEmitWeakSwiftAsyncExtendedFramePointerFlags() const {
+    return false;
+  }
 };
 
 } // end namespace llvm

llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp

@@ -1860,6 +1860,17 @@ bool AsmPrinter::doFinalization(Module &M) {
         continue;
       OutStreamer->emitSymbolAttribute(getSymbol(&GO), MCSA_WeakReference);
     }
+    if (shouldEmitWeakSwiftAsyncExtendedFramePointerFlags()) {
+      auto SymbolName = "swift_async_extendedFramePointerFlags";
+      auto Global = M.getGlobalVariable(SymbolName);
+      if (!Global) {
+        auto Int8PtrTy = Type::getInt8PtrTy(M.getContext());
+        Global = new GlobalVariable(M, Int8PtrTy, false,
+                                    GlobalValue::ExternalWeakLinkage, nullptr,
+                                    SymbolName);
+        OutStreamer->emitSymbolAttribute(getSymbol(Global), MCSA_WeakReference);
+      }
+    }
   }
 
   // Print aliases in topological order, that is, for each alias a = b,

llvm/lib/Target/AArch64/AArch64AsmPrinter.cpp

@@ -73,6 +73,7 @@ class AArch64AsmPrinter : public AsmPrinter {
   StackMaps SM;
   FaultMaps FM;
   const AArch64Subtarget *STI;
+  bool ShouldEmitWeakSwiftAsyncExtendedFramePointerFlags = false;
 
 public:
   AArch64AsmPrinter(TargetMachine &TM, std::unique_ptr<MCStreamer> Streamer)
@@ -186,6 +187,10 @@ private:
   using MInstToMCSymbol = std::map<const MachineInstr *, MCSymbol *>;
 
   MInstToMCSymbol LOHInstToLabel;
+
+  bool shouldEmitWeakSwiftAsyncExtendedFramePointerFlags() const override {
+    return ShouldEmitWeakSwiftAsyncExtendedFramePointerFlags;
+  }
 };
 
 } // end anonymous namespace
@@ -1132,6 +1137,15 @@ void AArch64AsmPrinter::emitInstruction(const MachineInstr *MI) {
   if (emitPseudoExpansionLowering(*OutStreamer, MI))
     return;
 
+  if (MI->getOpcode() == AArch64::ADRP) {
+    for (auto &Opd : MI->operands()) {
+      if (Opd.isSymbol() && StringRef(Opd.getSymbolName()) ==
+                                "swift_async_extendedFramePointerFlags") {
+        ShouldEmitWeakSwiftAsyncExtendedFramePointerFlags = true;
+      }
+    }
+  }
+
   if (AArch64FI->getLOHRelated().count(MI)) {
     // Generate a label for LOH related instruction
     MCSymbol *LOHLabel = createTempSymbol("loh");

llvm/lib/Target/X86/X86AsmPrinter.h

@@ -31,6 +31,7 @@ class LLVM_LIBRARY_VISIBILITY X86AsmPrinter : public AsmPrinter {
   FaultMaps FM;
   std::unique_ptr<MCCodeEmitter> CodeEmitter;
   bool EmitFPOData = false;
+  bool ShouldEmitWeakSwiftAsyncExtendedFramePointerFlags = false;
 
   // This utility class tracks the length of a stackmap instruction's 'shadow'.
   // It is used by the X86AsmPrinter to ensure that the stackmap shadow
@@ -151,6 +152,10 @@ public:
   bool runOnMachineFunction(MachineFunction &MF) override;
   void emitFunctionBodyStart() override;
   void emitFunctionBodyEnd() override;
+
+  bool shouldEmitWeakSwiftAsyncExtendedFramePointerFlags() const override {
+    return ShouldEmitWeakSwiftAsyncExtendedFramePointerFlags;
+  }
 };
 
 } // end namespace llvm

llvm/lib/Target/X86/X86MCInstLower.cpp

@@ -2410,6 +2410,15 @@ void X86AsmPrinter::emitInstruction(const MachineInstr *MI) {
   const X86RegisterInfo *RI =
       MF->getSubtarget<X86Subtarget>().getRegisterInfo();
 
+  if (MI->getOpcode() == X86::OR64rm) {
+    for (auto &Opd : MI->operands()) {
+      if (Opd.isSymbol() && StringRef(Opd.getSymbolName()) ==
+                                "swift_async_extendedFramePointerFlags") {
+        ShouldEmitWeakSwiftAsyncExtendedFramePointerFlags = true;
+      }
+    }
+  }
+
   // Add a comment about EVEX-2-VEX compression for AVX-512 instrs that
   // are compressed from EVEX encoding to VEX encoding.
   if (TM.Options.MCOptions.ShowMCEncoding) {

llvm/test/CodeGen/AArch64/swift-dynamic-async-frame.ll

@@ -23,11 +23,13 @@
 ; CHECK-DYNAMIC: adrp x16, _swift_async_extendedFramePointerFlags@GOTPAGE
 ; CHECK-DYNAMIC: ldr x16, [x16, _swift_async_extendedFramePointerFlags@GOTPAGEOFF]
 ; CHECK-DYNAMIC: orr x29, x29, x16
+; CHECK-DYNAMIC: .weak_reference _swift_async_extendedFramePointerFlags
 
 ; CHECK-DYNAMIC-32-LABEL: foo:
 ; CHECK-DYNAMIC-32: adrp x16, _swift_async_extendedFramePointerFlags@GOTPAGE
 ; CHECK-DYNAMIC-32: ldr w16, [x16, _swift_async_extendedFramePointerFlags@GOTPAGEOFF]
 ; CHECK-DYNAMIC-32: orr x29, x29, x16, lsl #32
+; CHECK-DYNAMIC-32: .weak_reference _swift_async_extendedFramePointerFlags
 
 define void @foo(i8* swiftasync) "frame-pointer"="all" {
   ret void

llvm/test/CodeGen/X86/swift-dynamic-async-frame.ll

@@ -12,6 +12,7 @@
 
 ; CHECK-DYNAMIC-LABEL: foo:
 ; CHECK-DYNAMIC: orq _swift_async_extendedFramePointerFlags@GOTPCREL(%rip), %rbp
+; CHECK-DYNAMIC: .weak_reference _swift_async_extendedFramePointerFlags
 
 ; CHECK-NEVER-LABEL: foo:
 ; CHECK-NEVER-NOT: btsq $60, %rbp