choose a more specific LLVM target on OS X when necessary

This behavior matches clang's behavior, and makes cross-language LTO
possible.

Fixes rust-lang#60235.

Author: froydnj

src/librustc_metadata/creader.rs

@@ -783,7 +783,7 @@ impl<'a> CrateLoader<'a> {
                 Sanitizer::Leak => LSAN_SUPPORTED_TARGETS,
                 Sanitizer::Memory => MSAN_SUPPORTED_TARGETS,
             };
-            if !supported_targets.contains(&&*self.sess.target.target.llvm_target) {
+            if !supported_targets.contains(&&*self.sess.opts.target_triple.triple()) {
                 self.sess.err(&format!("{:?}Sanitizer only works with the `{}` target",
                     sanitizer,
                     supported_targets.join("` or `")
@@ -794,7 +794,7 @@ impl<'a> CrateLoader<'a> {
             // firstyear 2017 - during testing I was unable to access an OSX machine
             // to make this work on different crate types. As a result, today I have
             // only been able to test and support linux as a target.
-            if self.sess.target.target.llvm_target == "x86_64-unknown-linux-gnu" {
+            if self.sess.opts.target_triple.triple() == "x86_64-unknown-linux-gnu" {
                 if !self.sess.crate_types.borrow().iter().all(|ct| {
                     match *ct {
                         // Link the runtime

src/librustc_target/spec/apple_base.rs

@@ -14,13 +14,7 @@ pub fn opts() -> TargetOptions {
     //
     // Here we detect what version is being requested, defaulting to 10.7. ELF
     // TLS is flagged as enabled if it looks to be supported.
-    let deployment_target = env::var("MACOSX_DEPLOYMENT_TARGET").ok();
-    let version = deployment_target.as_ref().and_then(|s| {
-        let mut i = s.splitn(2, '.');
-        i.next().and_then(|a| i.next().map(|b| (a, b)))
-    }).and_then(|(a, b)| {
-        a.parse::<u32>().and_then(|a| b.parse::<u32>().map(|b| (a, b))).ok()
-    }).unwrap_or((10, 7));
+    let version = macos_deployment_target().unwrap_or((10, 7));
 
     TargetOptions {
         // macOS has -dead_strip, which doesn't rely on function_sections
@@ -40,3 +34,27 @@ pub fn opts() -> TargetOptions {
         .. Default::default()
     }
 }
+
+fn macos_deployment_target() -> Option<(u32, u32)> {
+    let deployment_target = env::var("MACOSX_DEPLOYMENT_TARGET").ok();
+    let version = deployment_target.as_ref().and_then(|s| {
+        let mut i = s.splitn(2, '.');
+        i.next().and_then(|a| i.next().map(|b| (a, b)))
+    }).and_then(|(a, b)| {
+        a.parse::<u32>().and_then(|a| b.parse::<u32>().map(|b| (a, b))).ok()
+    });
+
+    version
+}
+
+pub fn macos_llvm_target(arch: &str) -> String {
+    let version = macos_deployment_target();
+    let llvm_target = match version {
+        Some((major, minor)) => {
+            format!("{}-apple-macosx{}.{}.0", arch, major, minor)
+        },
+        None => format!("{}-apple-darwin", arch)
+    };
+
+    llvm_target
+}

src/librustc_target/spec/i686_apple_darwin.rs

@@ -8,8 +8,14 @@ pub fn target() -> TargetResult {
     base.stack_probes = true;
     base.eliminate_frame_pointer = false;
 
+    // Clang automatically chooses a more specific target based on
+    // MACOSX_DEPLOYMENT_TARGET.  To enable cross-language LTO to work
+    // correctly, we do too.
+    let arch = "i686";
+    let llvm_target = super::apple_base::macos_llvm_target(&arch);
+
     Ok(Target {
-        llvm_target: "i686-apple-darwin".to_string(),
+        llvm_target: llvm_target,
         target_endian: "little".to_string(),
         target_pointer_width: "32".to_string(),
         target_c_int_width: "32".to_string(),

src/librustc_target/spec/x86_64_apple_darwin.rs

@@ -8,13 +8,19 @@ pub fn target() -> TargetResult {
     base.pre_link_args.insert(LinkerFlavor::Gcc, vec!["-m64".to_string()]);
     base.stack_probes = true;
 
+    // Clang automatically chooses a more specific target based on
+    // MACOSX_DEPLOYMENT_TARGET.  To enable cross-language LTO to work
+    // correctly, we do too.
+    let arch = "x86_64";
+    let llvm_target = super::apple_base::macos_llvm_target(&arch);
+
     Ok(Target {
-        llvm_target: "x86_64-apple-darwin".to_string(),
+        llvm_target: llvm_target,
         target_endian: "little".to_string(),
         target_pointer_width: "64".to_string(),
         target_c_int_width: "32".to_string(),
         data_layout: "e-m:o-i64:64-f80:128-n8:16:32:64-S128".to_string(),
-        arch: "x86_64".to_string(),
+        arch: arch.to_string(),
         target_os: "macos".to_string(),
         target_env: String::new(),
         target_vendor: "apple".to_string(),

src/test/codegen/i686-macosx-deployment-target.rs

@@ -0,0 +1,26 @@
+//
+// Checks that we correctly modify the target when MACOSX_DEPLOYMENT_TARGET is set.
+// See issue #60235.
+
+// compile-flags: -O --target=i686-apple-darwin --crate-type=rlib
+// rustc-env:MACOSX_DEPLOYMENT_TARGET=10.9
+#![feature(no_core, lang_items)]
+#![no_core]
+
+#[lang="sized"]
+trait Sized { }
+#[lang="freeze"]
+trait Freeze { }
+#[lang="copy"]
+trait Copy { }
+
+#[repr(C)]
+pub struct Bool {
+    b: bool,
+}
+
+// CHECK: target triple = "i686-apple-macosx10.9.0"
+#[no_mangle]
+pub extern "C" fn structbool() -> Bool {
+    Bool { b: true }
+}

src/test/codegen/x86_64-macosx-deployment-target.rs

@@ -0,0 +1,26 @@
+//
+// Checks that we correctly modify the target when MACOSX_DEPLOYMENT_TARGET is set.
+// See issue #60235.
+
+// compile-flags: -O --target=x86_64-apple-darwin --crate-type=rlib
+// rustc-env:MACOSX_DEPLOYMENT_TARGET=10.9
+#![feature(no_core, lang_items)]
+#![no_core]
+
+#[lang="sized"]
+trait Sized { }
+#[lang="freeze"]
+trait Freeze { }
+#[lang="copy"]
+trait Copy { }
+
+#[repr(C)]
+pub struct Bool {
+    b: bool,
+}
+
+// CHECK: target triple = "x86_64-apple-macosx10.9.0"
+#[no_mangle]
+pub extern "C" fn structbool() -> Bool {
+    Bool { b: true }
+}