From 68e126cad26fa5f1fead5de9a05c85a8557ae60d Mon Sep 17 00:00:00 2001
From: John McCall <rjmccall@apple.com>
Date: Wed, 12 Dec 2018 12:05:33 -0500
Subject: [PATCH] Revert "Future-proof the ARM64 ABI by not reserving the
 entire top byte."

This reverts commit 478d2b2552ee322212de9b12935869899dad3a06.
This patch does not work with our current assumptions about BridgeObject.
---
 stdlib/public/SwiftShims/System.h  | 5 ++---
 test/IRGen/bridge_object_arm64.sil | 4 ++--
 2 files changed, 4 insertions(+), 5 deletions(-)

diff --git a/stdlib/public/SwiftShims/System.h b/stdlib/public/SwiftShims/System.h
index e7d4df2d5f13c..a8fae1f724f96 100644
--- a/stdlib/public/SwiftShims/System.h
+++ b/stdlib/public/SwiftShims/System.h
@@ -136,10 +136,9 @@
 /// Darwin reserves the low 4GB of address space.
 #define SWIFT_ABI_DARWIN_ARM64_LEAST_VALID_POINTER 0x100000000ULL
 
-// TBI guarantees the top byte of pointers is unused, but ARMv8.5-A
-// claims the bottom four bits of that for memory tagging.
+// TBI guarantees the top byte of pointers is unused.
 // Heap objects are eight-byte aligned.
-#define SWIFT_ABI_ARM64_SWIFT_SPARE_BITS_MASK 0xF000000000000007ULL
+#define SWIFT_ABI_ARM64_SWIFT_SPARE_BITS_MASK 0xFF00000000000007ULL
 
 // Objective-C reserves just the high bit for tagged pointers.
 #define SWIFT_ABI_ARM64_OBJC_RESERVED_BITS_MASK 0x8000000000000000ULL
diff --git a/test/IRGen/bridge_object_arm64.sil b/test/IRGen/bridge_object_arm64.sil
index 3642d702a0ada..053cee1e8ae07 100644
--- a/test/IRGen/bridge_object_arm64.sil
+++ b/test/IRGen/bridge_object_arm64.sil
@@ -35,8 +35,8 @@ entry(%c : $C, %w : $Builtin.Word):
 // CHECK:         [[TAGGED_RESULT:%.*]] = bitcast [[BRIDGE]] %0 to [[C:%objc_object\*]]
 // CHECK:         br label %tagged-cont
 // CHECK:       not-tagged-pointer:
-// --                                                     0x0fff_ffff_ffff_fff8
-// CHECK:         [[MASKED_BITS:%.*]] = and i64 [[BOBITS]], 1152921504606846968
+// --                                                     0x00ff_ffff_ffff_fff8
+// CHECK:         [[MASKED_BITS:%.*]] = and i64 [[BOBITS]], 72057594037927928
 // CHECK:         [[MASKED_RESULT:%.*]] = inttoptr i64 [[MASKED_BITS]] to [[C]]
 // CHECK:         br label %tagged-cont
 // CHECK:      tagged-cont: