Rollup merge of #133463 - taiki-e:aarch64-asm-x18, r=Amanieu

Fix handling of x18 in AArch64 inline assembly on ohos/trusty or with -Zfixed-x18

Currently AArch64 inline assembly allows using x18 on ohos/trusty or with -Zfixed-x18.

7db7489f9b/compiler/rustc_target/src/asm/aarch64.rs (L74-L76)

However, x18 is reserved in these environments and should not be allowed in the input/output operands of inline assemblies as it is in Android, Windows, etc..

7db7489f9b/compiler/rustc_target/src/spec/targets/aarch64_unknown_linux_ohos.rs (L19)
7db7489f9b/compiler/rustc_target/src/spec/targets/aarch64_unknown_trusty.rs (L18)
7db7489f9b/compiler/rustc_codegen_llvm/src/llvm_util.rs (L764-L771)

(As for ohos, +reserve-x18 is [redundant](c417b7a695 (diff-0ddf23e0bf2b28b2d05f842f087d1e6f694e8e06d1765e8d0f10d47fddcdff9c)) since 7a966b9188 that starting using llvm's ohos targets. So removed it from target-spec.)

This fix may potentially break the code for tier 2 target (aarch64-unknown-linux-ohos). (As for others, aarch64-unknown-trusty is tier 3 and -Zfixed-x18 is unstable so breaking them should be fine.)
However, in any case, it seems suspicious that the code that is broken by this was sound.

r? `@Amanieu`

`@rustbot` label O-AArch64 +A-inline-assembly

compiler/rustc_target/src/asm/aarch64.rs

@@ -1,7 +1,7 @@
 use std::fmt;
 
 use rustc_data_structures::fx::FxIndexSet;
-use rustc_span::Symbol;
+use rustc_span::{Symbol, sym};
 
 use super::{InlineAsmArch, InlineAsmType, ModifierInfo};
 use crate::spec::{RelocModel, Target};
@@ -71,18 +71,26 @@ impl AArch64InlineAsmRegClass {
     }
 }
 
-pub(crate) fn target_reserves_x18(target: &Target) -> bool {
-    target.os == "android" || target.os == "fuchsia" || target.is_like_osx || target.is_like_windows
+pub(crate) fn target_reserves_x18(target: &Target, target_features: &FxIndexSet<Symbol>) -> bool {
+    // See isX18ReservedByDefault in LLVM for targets reserve x18 by default:
+    // https://github.com/llvm/llvm-project/blob/llvmorg-19.1.0/llvm/lib/TargetParser/AArch64TargetParser.cpp#L102-L105
+    // Note that +reserve-x18 is currently not set for the above targets.
+    target.os == "android"
+        || target.os == "fuchsia"
+        || target.env == "ohos"
+        || target.is_like_osx
+        || target.is_like_windows
+        || target_features.contains(&sym::reserve_x18)
 }
 
 fn reserved_x18(
     _arch: InlineAsmArch,
     _reloc_model: RelocModel,
-    _target_features: &FxIndexSet<Symbol>,
+    target_features: &FxIndexSet<Symbol>,
     target: &Target,
     _is_clobber: bool,
 ) -> Result<(), &'static str> {
-    if target_reserves_x18(target) {
+    if target_reserves_x18(target, target_features) {
         Err("x18 is a reserved register on this target")
     } else {
         Ok(())

compiler/rustc_target/src/asm/mod.rs

@@ -965,11 +965,13 @@ impl InlineAsmClobberAbi {
                 _ => Err(&["C", "system", "efiapi", "aapcs"]),
             },
             InlineAsmArch::AArch64 => match name {
-                "C" | "system" | "efiapi" => Ok(if aarch64::target_reserves_x18(target) {
-                    InlineAsmClobberAbi::AArch64NoX18
-                } else {
-                    InlineAsmClobberAbi::AArch64
-                }),
+                "C" | "system" | "efiapi" => {
+                    Ok(if aarch64::target_reserves_x18(target, target_features) {
+                        InlineAsmClobberAbi::AArch64NoX18
+                    } else {
+                        InlineAsmClobberAbi::AArch64
+                    })
+                }
                 _ => Err(&["C", "system", "efiapi"]),
             },
             InlineAsmArch::Arm64EC => match name {