Disallow the use of high byte registes as operands on x86_64

compiler/rustc_target/src/asm/arm.rs

@@ -68,7 +68,6 @@ fn frame_pointer_r11(
     _arch: InlineAsmArch,
     has_feature: impl FnMut(&str) -> bool,
     target: &Target,
-    _allocating: bool,
 ) -> Result<(), &'static str> {
     if !frame_pointer_is_r7(has_feature, target) {
         Err("the frame pointer (r11) cannot be used as an operand for inline asm")
@@ -81,7 +80,6 @@ fn frame_pointer_r7(
     _arch: InlineAsmArch,
     has_feature: impl FnMut(&str) -> bool,
     target: &Target,
-    _allocating: bool,
 ) -> Result<(), &'static str> {
     if frame_pointer_is_r7(has_feature, target) {
         Err("the frame pointer (r7) cannot be used as an operand for inline asm")

compiler/rustc_target/src/asm/mod.rs

@@ -90,7 +90,7 @@ macro_rules! def_regs {
                 match name {
                     $(
                         $($alias)|* | $reg_name => {
-                            $($filter(_arch, &mut _has_feature, _target, false)?;)?
+                            $($filter(_arch, &mut _has_feature, _target)?;)?
                             Ok(Self::$reg)
                         }
                     )*
@@ -114,7 +114,7 @@ macro_rules! def_regs {
             #[allow(unused_imports)]
             use super::{InlineAsmReg, InlineAsmRegClass};
             $(
-                if $($filter(_arch, &mut _has_feature, _target, true).is_ok() &&)? true {
+                if $($filter(_arch, &mut _has_feature, _target).is_ok() &&)? true {
                     if let Some(set) = _map.get_mut(&InlineAsmRegClass::$arch($arch_regclass::$class)) {
                         set.insert(InlineAsmReg::$arch($arch_reg::$reg));
                     }

compiler/rustc_target/src/asm/riscv.rs

@@ -52,7 +52,6 @@ fn not_e(
     _arch: InlineAsmArch,
     mut has_feature: impl FnMut(&str) -> bool,
     _target: &Target,
-    _allocating: bool,
 ) -> Result<(), &'static str> {
     if has_feature("e") {
         Err("register can't be used with the `e` target feature")

compiler/rustc_target/src/asm/x86.rs

@@ -133,7 +133,6 @@ fn x86_64_only(
     arch: InlineAsmArch,
     _has_feature: impl FnMut(&str) -> bool,
     _target: &Target,
-    _allocating: bool,
 ) -> Result<(), &'static str> {
     match arch {
         InlineAsmArch::X86 => Err("register is only available on x86_64"),
@@ -146,13 +145,9 @@ fn high_byte(
     arch: InlineAsmArch,
     _has_feature: impl FnMut(&str) -> bool,
     _target: &Target,
-    allocating: bool,
 ) -> Result<(), &'static str> {
     match arch {
-        InlineAsmArch::X86_64 if allocating => {
-            // The error message isn't actually used...
-            Err("high byte registers are not allocated by reg_byte")
-        }
+        InlineAsmArch::X86_64 => Err("high byte registers cannot be used as an operand on x86_64"),
         _ => Ok(()),
     }
 }

src/doc/unstable-book/src/library-features/asm.md

@@ -495,7 +495,7 @@ Here is the list of currently supported register classes:
 | x86 | `reg` | `ax`, `bx`, `cx`, `dx`, `si`, `di`, `r[8-15]` (x86-64 only) | `r` |
 | x86 | `reg_abcd` | `ax`, `bx`, `cx`, `dx` | `Q` |
 | x86-32 | `reg_byte` | `al`, `bl`, `cl`, `dl`, `ah`, `bh`, `ch`, `dh` | `q` |
-| x86-64 | `reg_byte` | `al`, `bl`, `cl`, `dl`, `sil`, `dil`, `r[8-15]b`, `ah`\*, `bh`\*, `ch`\*, `dh`\* | `q` |
+| x86-64 | `reg_byte`\* | `al`, `bl`, `cl`, `dl`, `sil`, `dil`, `r[8-15]b` | `q` |
 | x86 | `xmm_reg` | `xmm[0-7]` (x86) `xmm[0-15]` (x86-64) | `x` |
 | x86 | `ymm_reg` | `ymm[0-7]` (x86) `ymm[0-15]` (x86-64) | `x` |
 | x86 | `zmm_reg` | `zmm[0-7]` (x86) `zmm[0-31]` (x86-64) | `v` |
@@ -526,7 +526,7 @@ Here is the list of currently supported register classes:
 
 > **Note**: On x86 we treat `reg_byte` differently from `reg` because the compiler can allocate `al` and `ah` separately whereas `reg` reserves the whole register.
 >
-> Note #2: On x86-64 the high byte registers (e.g. `ah`) are only available when used as an explicit register. Specifying the `reg_byte` register class for an operand will always allocate a low byte register.
+> Note #2: On x86-64 the high byte registers (e.g. `ah`) are not available in the `reg_byte` register class.
 >
 > Note #3: NVPTX doesn't have a fixed register set, so named registers are not supported.
 >

src/test/assembly/asm/x86-types.rs

@@ -748,10 +748,11 @@ check_reg!(eax_f64 f64 "eax" "mov");
 // CHECK: #NO_APP
 check_reg!(eax_ptr ptr "eax" "mov");
 
-// CHECK-LABEL: ah_byte:
-// CHECK: #APP
-// CHECK: mov ah, ah
-// CHECK: #NO_APP
+// i686-LABEL: ah_byte:
+// i686: #APP
+// i686: mov ah, ah
+// i686: #NO_APP
+#[cfg(i686)]
 check_reg!(ah_byte i8 "ah" "mov");
 
 // CHECK-LABEL: xmm0_i32:

src/test/ui/asm/bad-reg.rs

@@ -37,6 +37,8 @@ fn main() {
         //~^ ERROR invalid register `mm0`: MMX registers are not currently supported as operands
         asm!("", in("k0") foo);
         //~^ ERROR invalid register `k0`: the k0 AVX mask register cannot be used as an operand
+        asm!("", in("ah") foo);
+        //~^ ERROR invalid register `ah`: high byte registers cannot be used as an operand
 
         // Explicit register conflicts
         // (except in/lateout which don't conflict)

src/test/ui/asm/bad-reg.stderr

@@ -94,49 +94,55 @@ error: invalid register `k0`: the k0 AVX mask register cannot be used as an oper
 LL |         asm!("", in("k0") foo);
    |                  ^^^^^^^^^^^^
 
+error: invalid register `ah`: high byte registers cannot be used as an operand on x86_64
+  --> $DIR/bad-reg.rs:40:18
+   |
+LL |         asm!("", in("ah") foo);
+   |                  ^^^^^^^^^^^^
+
 error: register `al` conflicts with register `ax`
-  --> $DIR/bad-reg.rs:44:33
+  --> $DIR/bad-reg.rs:46:33
    |
 LL |         asm!("", in("eax") foo, in("al") bar);
    |                  -------------  ^^^^^^^^^^^^ register `al`
    |                  |
    |                  register `ax`
 
 error: register `ax` conflicts with register `ax`
-  --> $DIR/bad-reg.rs:46:33
+  --> $DIR/bad-reg.rs:48:33
    |
 LL |         asm!("", in("rax") foo, out("rax") bar);
    |                  -------------  ^^^^^^^^^^^^^^ register `ax`
    |                  |
    |                  register `ax`
    |
 help: use `lateout` instead of `out` to avoid conflict
-  --> $DIR/bad-reg.rs:46:18
+  --> $DIR/bad-reg.rs:48:18
    |
 LL |         asm!("", in("rax") foo, out("rax") bar);
    |                  ^^^^^^^^^^^^^
 
 error: register `ymm0` conflicts with register `xmm0`
-  --> $DIR/bad-reg.rs:49:34
+  --> $DIR/bad-reg.rs:51:34
    |
 LL |         asm!("", in("xmm0") foo, in("ymm0") bar);
    |                  --------------  ^^^^^^^^^^^^^^ register `ymm0`
    |                  |
    |                  register `xmm0`
 
 error: register `ymm0` conflicts with register `xmm0`
-  --> $DIR/bad-reg.rs:51:34
+  --> $DIR/bad-reg.rs:53:34
    |
 LL |         asm!("", in("xmm0") foo, out("ymm0") bar);
    |                  --------------  ^^^^^^^^^^^^^^^ register `ymm0`
    |                  |
    |                  register `xmm0`
    |
 help: use `lateout` instead of `out` to avoid conflict
-  --> $DIR/bad-reg.rs:51:18
+  --> $DIR/bad-reg.rs:53:18
    |
 LL |         asm!("", in("xmm0") foo, out("ymm0") bar);
    |                  ^^^^^^^^^^^^^^
 
-error: aborting due to 18 previous errors
+error: aborting due to 19 previous errors