Reserve x18 on AArch64 and un-reserve x16

3 files changed, 9 insertions, 10 deletions

diff --git a/compiler/rustc_target/src/asm/aarch64.rs b/compiler/rustc_target/src/asm/aarch64.rs
index dd51574efca..f180eea01a3 100644
--- a/compiler/rustc_target/src/asm/aarch64.rs
+++ b/compiler/rustc_target/src/asm/aarch64.rs
@@ -83,8 +83,8 @@ def_regs! {
         x13: reg = ["x13", "w13"],
         x14: reg = ["x14", "w14"],
         x15: reg = ["x15", "w15"],
+        x16: reg = ["x16", "w16"],
         x17: reg = ["x17", "w17"],
-        x18: reg = ["x18", "w18"],
         x20: reg = ["x20", "w20"],
         x21: reg = ["x21", "w21"],
         x22: reg = ["x22", "w22"],
@@ -127,8 +127,8 @@ def_regs! {
         v29: vreg = ["v29", "b29", "h29", "s29", "d29", "q29"],
         v30: vreg = ["v30", "b30", "h30", "s30", "d30", "q30"],
         v31: vreg = ["v31", "b31", "h31", "s31", "d31", "q31"],
-        #error = ["x16", "w16"] =>
-            "x16 is used internally by LLVM and cannot be used as an operand for inline asm",
+        #error = ["x18", "w18"] =>
+            "x18 is used as a reserved register on some targets and cannot be used as an operand for inline asm",
         #error = ["x19", "w19"] =>
             "x19 is used internally by LLVM and cannot be used as an operand for inline asm",
         #error = ["x29", "w29", "fp", "wfp"] =>
diff --git a/library/std/src/sys/sgx/ext/arch.rs b/library/std/src/sys/sgx/ext/arch.rs
index a6718006fe4..b0170e67446 100644
--- a/library/std/src/sys/sgx/ext/arch.rs
+++ b/library/std/src/sys/sgx/ext/arch.rs
@@ -33,9 +33,9 @@ pub fn egetkey(request: &Align512<[u8; 512]>) -> Result<Align16<[u8; 16]>, u32>
 
         asm!(
             // rbx is reserved by LLVM
-            "xchg {}, rbx",
+            "xchg {0}, rbx",
             "enclu",
-            "mov rbx, {}",
+            "mov rbx, {0}",
             inout(reg) request => _,
             inlateout("eax") ENCLU_EGETKEY => error,
             in("rcx") out.as_mut_ptr(),
@@ -64,9 +64,9 @@ pub fn ereport(
 
         asm!(
             // rbx is reserved by LLVM
-            "xchg {}, rbx",
+            "xchg {0}, rbx",
             "enclu",
-            "mov rbx, {}",
+            "mov rbx, {0}",
             inout(reg) targetinfo => _,
             in("eax") ENCLU_EREPORT,
             in("rcx") reportdata,
diff --git a/src/doc/unstable-book/src/library-features/asm.md b/src/doc/unstable-book/src/library-features/asm.md
index 7c2bf621855..fa96e47ee03 100644
--- a/src/doc/unstable-book/src/library-features/asm.md
+++ b/src/doc/unstable-book/src/library-features/asm.md
@@ -681,7 +681,6 @@ Some registers cannot be used for input or output operands:
 | x86 | `mm[0-7]` | MMX registers are not currently supported (but may be in the future). |
 | x86 | `st([0-7])` | x87 registers are not currently supported (but may be in the future). |
 | AArch64 | `xzr` | This is a constant zero register which can't be modified. |
-| AArch64 | `x16` | This is used internally by LLVM for speculative load hardening. |
 | ARM | `pc` | This is the program counter, not a real register. |
 | ARM | `r9` | This is a reserved register on some ARM targets. |
 | MIPS | `$0` or `$zero` | This is a constant zero register which can't be modified. |
@@ -695,8 +694,8 @@ Some registers cannot be used for input or output operands:
 
 In some cases LLVM will allocate a "reserved register" for `reg` operands even though this register cannot be explicitly specified. Assembly code making use of reserved registers should be careful since `reg` operands may alias with those registers. Reserved registers are the frame pointer and base pointer
 - The frame pointer and LLVM base pointer on all architectures.
-- `x16` on AArch64.
-- `r6` and `r9` on ARM.
+- `r9` on ARM.
+- `x18` on AArch64.
 
 ## Template modifiers