[AArch64][Win] Emit SEH instructions for the swift async

context-related instructions in the prologue and the epilogue.

This fixes an error from checkARM64Instructions() in MCWin64EH.cpp.

Cherrypick from commit llvm@0ecd884

Author: hjyamauchi

llvm/lib/Target/AArch64/AArch64FrameLowering.cpp

@@ -1483,10 +1483,20 @@ void AArch64FrameLowering::emitPrologue(MachineFunction &MF,
         BuildMI(MBB, MBBI, DL, TII->get(AArch64::LOADgot), AArch64::X16)
             .addExternalSymbol("swift_async_extendedFramePointerFlags",
                                AArch64II::MO_GOT);
+        if (NeedsWinCFI) {
+          BuildMI(MBB, MBBI, DL, TII->get(AArch64::SEH_Nop))
+              .setMIFlags(MachineInstr::FrameSetup);
+          HasWinCFI = true;
+        }
         BuildMI(MBB, MBBI, DL, TII->get(AArch64::ORRXrs), AArch64::FP)
             .addUse(AArch64::FP)
             .addUse(AArch64::X16)
             .addImm(Subtarget.isTargetILP32() ? 32 : 0);
+        if (NeedsWinCFI) {
+          BuildMI(MBB, MBBI, DL, TII->get(AArch64::SEH_Nop))
+              .setMIFlags(MachineInstr::FrameSetup);
+          HasWinCFI = true;
+        }
         break;
       }
       [[fallthrough]];
@@ -1497,6 +1507,11 @@ void AArch64FrameLowering::emitPrologue(MachineFunction &MF,
           .addUse(AArch64::FP)
           .addImm(0x1100)
           .setMIFlag(MachineInstr::FrameSetup);
+      if (NeedsWinCFI) {
+        BuildMI(MBB, MBBI, DL, TII->get(AArch64::SEH_Nop))
+            .setMIFlags(MachineInstr::FrameSetup);
+        HasWinCFI = true;
+      }
       break;
 
     case SwiftAsyncFramePointerMode::Never:
@@ -1626,11 +1641,20 @@ void AArch64FrameLowering::emitPrologue(MachineFunction &MF,
         bool HaveInitialContext = Attrs.hasAttrSomewhere(Attribute::SwiftAsync);
         if (HaveInitialContext)
           MBB.addLiveIn(AArch64::X22);
+        Register Reg = HaveInitialContext ? AArch64::X22 : AArch64::XZR;
         BuildMI(MBB, MBBI, DL, TII->get(AArch64::StoreSwiftAsyncContext))
-            .addUse(HaveInitialContext ? AArch64::X22 : AArch64::XZR)
+            .addUse(Reg)
             .addUse(AArch64::SP)
             .addImm(FPOffset - 8)
             .setMIFlags(MachineInstr::FrameSetup);
+        if (NeedsWinCFI) {
+          // WinCFI and arm64e, where StoreSwiftAsyncContext is expanded
+          // to multiple instructions, should be mutually-exclusive.
+          assert(Subtarget.getTargetTriple().getArchName() != "arm64e");
+          BuildMI(MBB, MBBI, DL, TII->get(AArch64::SEH_Nop))
+              .setMIFlags(MachineInstr::FrameSetup);
+          HasWinCFI = true;
+        }
       }
 
       // Issue    sub fp, sp, FPOffset or
@@ -2165,6 +2189,11 @@ void AArch64FrameLowering::emitEpilogue(MachineFunction &MF,
           .addUse(AArch64::FP)
           .addImm(0x10fe)
           .setMIFlag(MachineInstr::FrameDestroy);
+      if (NeedsWinCFI) {
+        BuildMI(MBB, MBBI, DL, TII->get(AArch64::SEH_Nop))
+            .setMIFlags(MachineInstr::FrameDestroy);
+        HasWinCFI = true;
+      }
       break;
 
     case SwiftAsyncFramePointerMode::Never:

llvm/test/CodeGen/AArch64/swift-async-context-seh.ll

@@ -0,0 +1,24 @@
+; RUN: rm -rf %t && mkdir -p %t
+; RUN: llc -mtriple aarch64-unknown-windows-msvc %s -o - | FileCheck %s
+; RUN: llc -mtriple aarch64-unknown-windows-msvc -filetype obj %s -o %t/a.o
+
+; Check that the prologue/epilogue instructions for the swift async
+; context have an associated SEH instruction and that it doesn't error
+; when the output is an object file.
+
+; CHECK: orr     x29, x29, #0x1000000000000000
+; CHECK-NEXT: .seh_nop
+; CHECK:  str     x22, [sp, #16]
+; CHECK-NEXT: .seh_nop
+; CHECK: and     x29, x29, #0xefffffffffffffff
+; CHECK-NEXT: .seh_nop
+
+declare ptr @llvm.swift.async.context.addr()
+
+define internal swifttailcc void @test(ptr nocapture readonly swiftasync %0) {
+entryresume.0:
+  %1 = load ptr, ptr %0, align 8
+  %2 = tail call ptr @llvm.swift.async.context.addr()
+  store ptr %1, ptr %2, align 8
+  ret void
+}