Move versioned LLVM target creation to rustc_codegen_ssa

The OS version depends on the deployment target environment variables,
the access of which we want to move to later in the compilation pipeline
that has access to more information, for example `env_depinfo`.

5 files changed, 182 insertions, 10 deletions

diff --git a/compiler/rustc_codegen_ssa/src/back/apple.rs b/compiler/rustc_codegen_ssa/src/back/apple.rs
new file mode 100644
index 00000000000..939ce2e1a03
--- /dev/null
+++ b/compiler/rustc_codegen_ssa/src/back/apple.rs
@@ -0,0 +1,127 @@
+use std::env;
+use std::num::ParseIntError;
+
+use rustc_session::Session;
+use rustc_target::spec::Target;
+
+#[cfg(test)]
+mod tests;
+
+/// Deployment target or SDK version.
+///
+/// The size of the numbers in here are limited by Mach-O's `LC_BUILD_VERSION`.
+type OSVersion = (u16, u8, u8);
+
+/// Parse an OS version triple (SDK version or deployment target).
+fn parse_version(version: &str) -> Result<OSVersion, ParseIntError> {
+    if let Some((major, minor)) = version.split_once('.') {
+        let major = major.parse()?;
+        if let Some((minor, patch)) = minor.split_once('.') {
+            Ok((major, minor.parse()?, patch.parse()?))
+        } else {
+            Ok((major, minor.parse()?, 0))
+        }
+    } else {
+        Ok((version.parse()?, 0, 0))
+    }
+}
+
+/// Minimum operating system versions currently supported by `rustc`.
+fn os_minimum_deployment_target(os: &str) -> OSVersion {
+    // When bumping a version in here, remember to update the platform-support docs too.
+    //
+    // NOTE: The defaults may change in future `rustc` versions, so if you are looking for the
+    // default deployment target, prefer:
+    // ```
+    // $ rustc --print deployment-target
+    // ```
+    match os {
+        "macos" => (10, 12, 0),
+        "ios" => (10, 0, 0),
+        "tvos" => (10, 0, 0),
+        "watchos" => (5, 0, 0),
+        "visionos" => (1, 0, 0),
+        _ => unreachable!("tried to get deployment target for non-Apple platform"),
+    }
+}
+
+/// The deployment target for the given target.
+///
+/// This is similar to `os_minimum_deployment_target`, except that on certain targets it makes sense
+/// to raise the minimum OS version.
+///
+/// This matches what LLVM does, see in part:
+/// <https://github.com/llvm/llvm-project/blob/llvmorg-18.1.8/llvm/lib/TargetParser/Triple.cpp#L1900-L1932>
+fn minimum_deployment_target(target: &Target) -> OSVersion {
+    match (&*target.os, &*target.arch, &*target.abi) {
+        ("macos", "aarch64", _) => (11, 0, 0),
+        ("ios", "aarch64", "macabi") => (14, 0, 0),
+        ("ios", "aarch64", "sim") => (14, 0, 0),
+        ("ios", _, _) if target.llvm_target.starts_with("arm64e") => (14, 0, 0),
+        // Mac Catalyst defaults to 13.1 in Clang.
+        ("ios", _, "macabi") => (13, 1, 0),
+        ("tvos", "aarch64", "sim") => (14, 0, 0),
+        ("watchos", "aarch64", "sim") => (7, 0, 0),
+        (os, _, _) => os_minimum_deployment_target(os),
+    }
+}
+
+/// Name of the environment variable used to fetch the deployment target on the given OS.
+fn deployment_target_env_var(os: &str) -> &'static str {
+    match os {
+        "macos" => "MACOSX_DEPLOYMENT_TARGET",
+        "ios" => "IPHONEOS_DEPLOYMENT_TARGET",
+        "watchos" => "WATCHOS_DEPLOYMENT_TARGET",
+        "tvos" => "TVOS_DEPLOYMENT_TARGET",
+        "visionos" => "XROS_DEPLOYMENT_TARGET",
+        _ => unreachable!("tried to get deployment target env var for non-Apple platform"),
+    }
+}
+
+/// Get the deployment target based on the standard environment variables, or fall back to the
+/// minimum version supported by `rustc`.
+pub fn deployment_target(sess: &Session) -> OSVersion {
+    let min = minimum_deployment_target(&sess.target);
+
+    if let Ok(deployment_target) = env::var(deployment_target_env_var(&sess.target.os)) {
+        match parse_version(&deployment_target) {
+            // It is common that the deployment target is set too low, e.g. on macOS Aarch64 to also
+            // target older x86_64, the user may set a lower deployment target than supported.
+            //
+            // To avoid such issues, we silently raise the deployment target here.
+            // FIXME: We want to show a warning when `version < os_min`.
+            Ok(version) => version.max(min),
+            // FIXME: Report erroneous environment variable to user.
+            Err(_) => min,
+        }
+    } else {
+        // If no deployment target variable is set, default to the minimum found above.
+        min
+    }
+}
+
+pub(super) fn add_version_to_llvm_target(
+    llvm_target: &str,
+    deployment_target: OSVersion,
+) -> String {
+    let mut components = llvm_target.split("-");
+    let arch = components.next().expect("apple target should have arch");
+    let vendor = components.next().expect("apple target should have vendor");
+    let os = components.next().expect("apple target should have os");
+    let environment = components.next();
+    assert_eq!(components.next(), None, "too many LLVM triple components");
+
+    let (major, minor, patch) = deployment_target;
+
+    assert!(
+        !os.contains(|c: char| c.is_ascii_digit()),
+        "LLVM target must not already be versioned"
+    );
+
+    if let Some(env) = environment {
+        // Insert version into OS, before environment
+        format!("{arch}-{vendor}-{os}{major}.{minor}.{patch}-{env}")
+    } else {
+        format!("{arch}-{vendor}-{os}{major}.{minor}.{patch}")
+    }
+}
diff --git a/compiler/rustc_codegen_ssa/src/back/apple/tests.rs b/compiler/rustc_codegen_ssa/src/back/apple/tests.rs
new file mode 100644
index 00000000000..7ccda5a8190
--- /dev/null
+++ b/compiler/rustc_codegen_ssa/src/back/apple/tests.rs
@@ -0,0 +1,21 @@
+use super::{add_version_to_llvm_target, parse_version};
+
+#[test]
+fn test_add_version_to_llvm_target() {
+    assert_eq!(
+        add_version_to_llvm_target("aarch64-apple-macosx", (10, 14, 1)),
+        "aarch64-apple-macosx10.14.1"
+    );
+    assert_eq!(
+        add_version_to_llvm_target("aarch64-apple-ios-simulator", (16, 1, 0)),
+        "aarch64-apple-ios16.1.0-simulator"
+    );
+}
+
+#[test]
+fn test_parse_version() {
+    assert_eq!(parse_version("10"), Ok((10, 0, 0)));
+    assert_eq!(parse_version("10.12"), Ok((10, 12, 0)));
+    assert_eq!(parse_version("10.12.6"), Ok((10, 12, 6)));
+    assert_eq!(parse_version("9999.99.99"), Ok((9999, 99, 99)));
+}
diff --git a/compiler/rustc_codegen_ssa/src/back/link.rs b/compiler/rustc_codegen_ssa/src/back/link.rs
index 34dc599e4fd..b01a62b394b 100644
--- a/compiler/rustc_codegen_ssa/src/back/link.rs
+++ b/compiler/rustc_codegen_ssa/src/back/link.rs
@@ -40,7 +40,7 @@ use rustc_target::spec::crt_objects::CrtObjects;
 use rustc_target::spec::{
     Cc, LinkOutputKind, LinkSelfContainedComponents, LinkSelfContainedDefault, LinkerFeatures,
     LinkerFlavor, LinkerFlavorCli, Lld, PanicStrategy, RelocModel, RelroLevel, SanitizerSet,
-    SplitDebuginfo, current_apple_deployment_target,
+    SplitDebuginfo,
 };
 use tempfile::Builder as TempFileBuilder;
 use tracing::{debug, info, warn};
@@ -50,6 +50,7 @@ use super::command::Command;
 use super::linker::{self, Linker};
 use super::metadata::{MetadataPosition, create_wrapper_file};
 use super::rpath::{self, RPathConfig};
+use super::{apple, versioned_llvm_target};
 use crate::{
     CodegenResults, CompiledModule, CrateInfo, NativeLib, common, errors,
     looks_like_rust_object_file,
@@ -2447,7 +2448,7 @@ fn add_order_independent_options(
     if flavor == LinkerFlavor::Llbc {
         cmd.link_args(&[
             "--target",
-            sess.target.llvm_target.as_ref(),
+            &versioned_llvm_target(sess),
             "--target-cpu",
             &codegen_results.crate_info.target_cpu,
         ]);
@@ -3039,7 +3040,7 @@ fn add_apple_link_args(cmd: &mut dyn Linker, sess: &Session, flavor: LinkerFlavo
             _ => bug!("invalid OS/ABI combination for Apple target: {target_os}, {target_abi}"),
         };
 
-        let (major, minor, patch) = current_apple_deployment_target(&sess.target);
+        let (major, minor, patch) = apple::deployment_target(sess);
         let min_version = format!("{major}.{minor}.{patch}");
 
         // The SDK version is used at runtime when compiling with a newer SDK / version of Xcode:
@@ -3109,7 +3110,7 @@ fn add_apple_link_args(cmd: &mut dyn Linker, sess: &Session, flavor: LinkerFlavo
 
             // The presence of `-mmacosx-version-min` makes CC default to
             // macOS, and it sets the deployment target.
-            let (major, minor, patch) = current_apple_deployment_target(&sess.target);
+            let (major, minor, patch) = apple::deployment_target(sess);
             // Intentionally pass this as a single argument, Clang doesn't
             // seem to like it otherwise.
             cmd.cc_arg(&format!("-mmacosx-version-min={major}.{minor}.{patch}"));
@@ -3119,7 +3120,7 @@ fn add_apple_link_args(cmd: &mut dyn Linker, sess: &Session, flavor: LinkerFlavo
             //
             // We avoid `-m32`/`-m64`, as this is already encoded by `-arch`.
         } else {
-            cmd.cc_args(&["-target", &sess.target.llvm_target]);
+            cmd.cc_args(&["-target", &versioned_llvm_target(sess)]);
         }
     }
 }
@@ -3345,7 +3346,7 @@ fn add_lld_args(
         // targeting a different linker flavor on macOS, and that's also always
         // the case when targeting WASM.
         if sess.target.linker_flavor != sess.host.linker_flavor {
-            cmd.cc_arg(format!("--target={}", sess.target.llvm_target));
+            cmd.cc_arg(format!("--target={}", versioned_llvm_target(sess)));
         }
     }
 }
diff --git a/compiler/rustc_codegen_ssa/src/back/metadata.rs b/compiler/rustc_codegen_ssa/src/back/metadata.rs
index 4c25c85569b..1b11fe661db 100644
--- a/compiler/rustc_codegen_ssa/src/back/metadata.rs
+++ b/compiler/rustc_codegen_ssa/src/back/metadata.rs
@@ -22,6 +22,8 @@ use rustc_span::sym;
 use rustc_target::abi::Endian;
 use rustc_target::spec::{RelocModel, Target, ef_avr_arch};
 
+use super::apple;
+
 /// The default metadata loader. This is used by cg_llvm and cg_clif.
 ///
 /// # Metadata location
@@ -238,7 +240,7 @@ pub(crate) fn create_object_file(sess: &Session) -> Option<write::Object<'static
             file.set_macho_cpu_subtype(object::macho::CPU_SUBTYPE_ARM64E);
         }
 
-        file.set_macho_build_version(macho_object_build_version_for_target(&sess.target))
+        file.set_macho_build_version(macho_object_build_version_for_target(sess))
     }
     if binary_format == BinaryFormat::Coff {
         // Disable the default mangler to avoid mangling the special "@feat.00" symbol name.
@@ -392,7 +394,7 @@ pub(crate) fn create_object_file(sess: &Session) -> Option<write::Object<'static
 ///
 /// Since Xcode 15, Apple's LD apparently requires object files to use this load command, so this
 /// returns the `MachOBuildVersion` for the target to do so.
-fn macho_object_build_version_for_target(target: &Target) -> object::write::MachOBuildVersion {
+fn macho_object_build_version_for_target(sess: &Session) -> object::write::MachOBuildVersion {
     /// The `object` crate demands "X.Y.Z encoded in nibbles as xxxx.yy.zz"
     /// e.g. minOS 14.0 = 0x000E0000, or SDK 16.2 = 0x00100200
     fn pack_version((major, minor, patch): (u16, u8, u8)) -> u32 {
@@ -401,8 +403,8 @@ fn macho_object_build_version_for_target(target: &Target) -> object::write::Mach
     }
 
     let platform =
-        rustc_target::spec::current_apple_platform(target).expect("unknown Apple target OS");
-    let min_os = rustc_target::spec::current_apple_deployment_target(target);
+        rustc_target::spec::current_apple_platform(&sess.target).expect("unknown Apple target OS");
+    let min_os = apple::deployment_target(sess);
 
     let mut build_version = object::write::MachOBuildVersion::default();
     build_version.platform = platform;
diff --git a/compiler/rustc_codegen_ssa/src/back/mod.rs b/compiler/rustc_codegen_ssa/src/back/mod.rs
index 2b3a2e3a369..64b5d4569ec 100644
--- a/compiler/rustc_codegen_ssa/src/back/mod.rs
+++ b/compiler/rustc_codegen_ssa/src/back/mod.rs
@@ -1,3 +1,8 @@
+use std::borrow::Cow;
+
+use rustc_session::Session;
+
+pub mod apple;
 pub mod archive;
 pub(crate) mod command;
 pub mod link;
@@ -7,3 +12,19 @@ pub mod metadata;
 pub(crate) mod rpath;
 pub mod symbol_export;
 pub mod write;
+
+/// The target triple depends on the deployment target, and is required to
+/// enable features such as cross-language LTO, and for picking the right
+/// Mach-O commands.
+///
+/// Certain optimizations also depend on the deployment target.
+pub fn versioned_llvm_target(sess: &Session) -> Cow<'_, str> {
+    if sess.target.is_like_osx {
+        apple::add_version_to_llvm_target(&sess.target.llvm_target, apple::deployment_target(sess))
+            .into()
+    } else {
+        // FIXME(madsmtm): Certain other targets also include a version,
+        // we might want to move that here as well.
+        Cow::Borrowed(&sess.target.llvm_target)
+    }
+}