Index: llvm/lib/Target/AArch64/GISel/AArch64CallLowering.cpp
===================================================================
--- llvm/lib/Target/AArch64/GISel/AArch64CallLowering.cpp
+++ llvm/lib/Target/AArch64/GISel/AArch64CallLowering.cpp
@@ -623,7 +623,7 @@
   uint64_t StackOffset = Assigner.StackOffset;
   if (F.isVarArg()) {
     auto &Subtarget = MF.getSubtarget<AArch64Subtarget>();
-    if (!Subtarget.isTargetDarwin()) {
+    if (!Subtarget.isTargetDarwin() || Subtarget.isCallingConvWin64(F.getCallingConv())) {
         // FIXME: we need to reimplement saveVarArgsRegisters from
       // AArch64ISelLowering.
       return false;
Index: llvm/test/CodeGen/AArch64/aarch64_win64cc_vararg.ll
===================================================================
--- llvm/test/CodeGen/AArch64/aarch64_win64cc_vararg.ll
+++ llvm/test/CodeGen/AArch64/aarch64_win64cc_vararg.ll
@@ -1,7 +1,24 @@
 ; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
 ; RUN: llc < %s -mtriple=aarch64-linux-gnu | FileCheck %s
+; RUN: llc < %s -mtriple=arm64-apple-ios -global-isel=1 -global-isel-abort=0 | FileCheck %s --check-prefix=CHECK-DARWIN
 
 define win64cc void @pass_va(i32 %count, ...) nounwind {
+; CHECK-LINUX-LABEL: pass_va:
+; CHECK-LINUX:       // %bb.0: // %entry
+; CHECK-LINUX-NEXT:    sub sp, sp, #96
+; CHECK-LINUX-NEXT:    add x8, sp, #40
+; CHECK-LINUX-NEXT:    add x0, sp, #40
+; CHECK-LINUX-NEXT:    stp x30, x18, [sp, #16] // 16-byte Folded Spill
+; CHECK-LINUX-NEXT:    stp x3, x4, [sp, #56]
+; CHECK-LINUX-NEXT:    stp x1, x2, [sp, #40]
+; CHECK-LINUX-NEXT:    stp x5, x6, [sp, #72]
+; CHECK-LINUX-NEXT:    str x7, [sp, #88]
+; CHECK-LINUX-NEXT:    str x8, [sp, #8]
+; CHECK-LINUX-NEXT:    bl other_func
+; CHECK-LINUX-NEXT:    ldp x30, x18, [sp, #16] // 16-byte Folded Reload
+; CHECK-LINUX-NEXT:    add sp, sp, #96
+; CHECK-LINUX-NEXT:    ret
+;
 ; CHECK-LABEL: pass_va:
 ; CHECK:       // %bb.0: // %entry
 ; CHECK-NEXT:    sub sp, sp, #96
@@ -17,6 +34,22 @@
 ; CHECK-NEXT:    ldp x30, x18, [sp, #16] // 16-byte Folded Reload
 ; CHECK-NEXT:    add sp, sp, #96
 ; CHECK-NEXT:    ret
+;
+; CHECK-DARWIN-LABEL: pass_va:
+; CHECK-DARWIN:       ; %bb.0: ; %entry
+; CHECK-DARWIN-NEXT:    str x18, [sp, #-96]! ; 8-byte Folded Spill
+; CHECK-DARWIN-NEXT:    add x8, sp, #40
+; CHECK-DARWIN-NEXT:    add x0, sp, #40
+; CHECK-DARWIN-NEXT:    stp x29, x30, [sp, #16] ; 16-byte Folded Spill
+; CHECK-DARWIN-NEXT:    stp x3, x4, [sp, #56]
+; CHECK-DARWIN-NEXT:    stp x1, x2, [sp, #40]
+; CHECK-DARWIN-NEXT:    stp x5, x6, [sp, #72]
+; CHECK-DARWIN-NEXT:    str x7, [sp, #88]
+; CHECK-DARWIN-NEXT:    str x8, [sp, #8]
+; CHECK-DARWIN-NEXT:    bl _other_func
+; CHECK-DARWIN-NEXT:    ldp x29, x30, [sp, #16] ; 16-byte Folded Reload
+; CHECK-DARWIN-NEXT:    ldr x18, [sp], #96 ; 8-byte Folded Reload
+; CHECK-DARWIN-NEXT:    ret
 entry:
   %ap = alloca ptr, align 8
   call void @llvm.va_start(ptr %ap)
@@ -31,6 +64,15 @@
 declare void @llvm.va_copy(ptr, ptr) nounwind
 
 define win64cc ptr @f9(i64 %a0, i64 %a1, i64 %a2, i64 %a3, i64 %a4, i64 %a5, i64 %a6, i64 %a7, i64 %a8, ...) nounwind {
+; CHECK-LINUX-LABEL: f9:
+; CHECK-LINUX:       // %bb.0: // %entry
+; CHECK-LINUX-NEXT:    str x18, [sp, #-16]! // 8-byte Folded Spill
+; CHECK-LINUX-NEXT:    add x8, sp, #24
+; CHECK-LINUX-NEXT:    add x0, sp, #24
+; CHECK-LINUX-NEXT:    str x8, [sp, #8]
+; CHECK-LINUX-NEXT:    ldr x18, [sp], #16 // 8-byte Folded Reload
+; CHECK-LINUX-NEXT:    ret
+;
 ; CHECK-LABEL: f9:
 ; CHECK:       // %bb.0: // %entry
 ; CHECK-NEXT:    str x18, [sp, #-16]! // 8-byte Folded Spill
@@ -39,6 +81,15 @@
 ; CHECK-NEXT:    str x8, [sp, #8]
 ; CHECK-NEXT:    ldr x18, [sp], #16 // 8-byte Folded Reload
 ; CHECK-NEXT:    ret
+;
+; CHECK-DARWIN-LABEL: f9:
+; CHECK-DARWIN:       ; %bb.0: ; %entry
+; CHECK-DARWIN-NEXT:    str x18, [sp, #-16]! ; 8-byte Folded Spill
+; CHECK-DARWIN-NEXT:    add x8, sp, #24
+; CHECK-DARWIN-NEXT:    add x0, sp, #24
+; CHECK-DARWIN-NEXT:    str x8, [sp, #8]
+; CHECK-DARWIN-NEXT:    ldr x18, [sp], #16 ; 8-byte Folded Reload
+; CHECK-DARWIN-NEXT:    ret
 entry:
   %ap = alloca ptr, align 8
   call void @llvm.va_start(ptr %ap)
@@ -47,6 +98,15 @@
 }
 
 define win64cc ptr @f8(i64 %a0, i64 %a1, i64 %a2, i64 %a3, i64 %a4, i64 %a5, i64 %a6, i64 %a7, ...) nounwind {
+; CHECK-LINUX-LABEL: f8:
+; CHECK-LINUX:       // %bb.0: // %entry
+; CHECK-LINUX-NEXT:    str x18, [sp, #-16]! // 8-byte Folded Spill
+; CHECK-LINUX-NEXT:    add x8, sp, #16
+; CHECK-LINUX-NEXT:    add x0, sp, #16
+; CHECK-LINUX-NEXT:    str x8, [sp, #8]
+; CHECK-LINUX-NEXT:    ldr x18, [sp], #16 // 8-byte Folded Reload
+; CHECK-LINUX-NEXT:    ret
+;
 ; CHECK-LABEL: f8:
 ; CHECK:       // %bb.0: // %entry
 ; CHECK-NEXT:    str x18, [sp, #-16]! // 8-byte Folded Spill
@@ -55,6 +115,15 @@
 ; CHECK-NEXT:    str x8, [sp, #8]
 ; CHECK-NEXT:    ldr x18, [sp], #16 // 8-byte Folded Reload
 ; CHECK-NEXT:    ret
+;
+; CHECK-DARWIN-LABEL: f8:
+; CHECK-DARWIN:       ; %bb.0: ; %entry
+; CHECK-DARWIN-NEXT:    str x18, [sp, #-16]! ; 8-byte Folded Spill
+; CHECK-DARWIN-NEXT:    add x8, sp, #16
+; CHECK-DARWIN-NEXT:    add x0, sp, #16
+; CHECK-DARWIN-NEXT:    str x8, [sp, #8]
+; CHECK-DARWIN-NEXT:    ldr x18, [sp], #16 ; 8-byte Folded Reload
+; CHECK-DARWIN-NEXT:    ret
 entry:
   %ap = alloca ptr, align 8
   call void @llvm.va_start(ptr %ap)
@@ -63,6 +132,16 @@
 }
 
 define win64cc ptr @f7(i64 %a0, i64 %a1, i64 %a2, i64 %a3, i64 %a4, i64 %a5, i64 %a6, ...) nounwind {
+; CHECK-LINUX-LABEL: f7:
+; CHECK-LINUX:       // %bb.0: // %entry
+; CHECK-LINUX-NEXT:    str x18, [sp, #-32]! // 8-byte Folded Spill
+; CHECK-LINUX-NEXT:    add x8, sp, #24
+; CHECK-LINUX-NEXT:    add x0, sp, #24
+; CHECK-LINUX-NEXT:    str x7, [sp, #24]
+; CHECK-LINUX-NEXT:    str x8, [sp, #8]
+; CHECK-LINUX-NEXT:    ldr x18, [sp], #32 // 8-byte Folded Reload
+; CHECK-LINUX-NEXT:    ret
+;
 ; CHECK-LABEL: f7:
 ; CHECK:       // %bb.0: // %entry
 ; CHECK-NEXT:    str x18, [sp, #-32]! // 8-byte Folded Spill
@@ -72,6 +151,16 @@
 ; CHECK-NEXT:    str x8, [sp, #8]
 ; CHECK-NEXT:    ldr x18, [sp], #32 // 8-byte Folded Reload
 ; CHECK-NEXT:    ret
+;
+; CHECK-DARWIN-LABEL: f7:
+; CHECK-DARWIN:       ; %bb.0: ; %entry
+; CHECK-DARWIN-NEXT:    str x18, [sp, #-32]! ; 8-byte Folded Spill
+; CHECK-DARWIN-NEXT:    add x8, sp, #24
+; CHECK-DARWIN-NEXT:    add x0, sp, #24
+; CHECK-DARWIN-NEXT:    str x7, [sp, #24]
+; CHECK-DARWIN-NEXT:    str x8, [sp, #8]
+; CHECK-DARWIN-NEXT:    ldr x18, [sp], #32 ; 8-byte Folded Reload
+; CHECK-DARWIN-NEXT:    ret
 entry:
   %ap = alloca ptr, align 8
   call void @llvm.va_start(ptr %ap)