8 files changed, 49 insertions, 18 deletions
diff --git a/src/librustc/session/mod.rs b/src/librustc/session/mod.rs
index ef81cd3a457..c8c0d4c38a2 100644
--- a/src/librustc/session/mod.rs
+++ b/src/librustc/session/mod.rs
@@ -649,13 +649,6 @@ impl Session {
         }
     }
 
-    pub fn target_cpu(&self) -> &str {
-        match self.opts.cg.target_cpu {
-            Some(ref s) => &**s,
-            None => &*self.target.target.options.cpu
-        }
-    }
-
     pub fn must_not_eliminate_frame_pointers(&self) -> bool {
         if let Some(x) = self.opts.cg.force_frame_pointers {
             x
diff --git a/src/librustc_codegen_llvm/attributes.rs b/src/librustc_codegen_llvm/attributes.rs
index 2b64642b766..c8a2b47e98d 100644
--- a/src/librustc_codegen_llvm/attributes.rs
+++ b/src/librustc_codegen_llvm/attributes.rs
@@ -124,7 +124,8 @@ pub fn llvm_target_features(sess: &Session) -> impl Iterator<Item = &str> {
 }
 
 pub fn apply_target_cpu_attr(cx: &CodegenCx<'ll, '_>, llfn: &'ll Value) {
-    let target_cpu = CString::new(cx.tcx.sess.target_cpu().to_string()).unwrap();
+    let cpu = llvm_util::target_cpu(cx.tcx.sess);
+    let target_cpu = CString::new(cpu).unwrap();
     llvm::AddFunctionAttrStringValue(
             llfn,
             llvm::AttributePlace::Function,
diff --git a/src/librustc_codegen_llvm/back/linker.rs b/src/librustc_codegen_llvm/back/linker.rs
index a429e8f2d81..eee60b262a1 100644
--- a/src/librustc_codegen_llvm/back/linker.rs
+++ b/src/librustc_codegen_llvm/back/linker.rs
@@ -26,6 +26,7 @@ use rustc::session::config::{self, CrateType, OptLevel, DebugInfo,
 use rustc::ty::TyCtxt;
 use rustc_target::spec::{LinkerFlavor, LldFlavor};
 use serialize::{json, Encoder};
+use llvm_util;
 
 /// For all the linkers we support, and information they might
 /// need out of the shared crate context before we get rid of it.
@@ -202,7 +203,7 @@ impl<'a> GccLinker<'a> {
         };
 
         self.linker_arg(&format!("-plugin-opt={}", opt_level));
-        self.linker_arg(&format!("-plugin-opt=mcpu={}", self.sess.target_cpu()));
+        self.linker_arg(&format!("-plugin-opt=mcpu={}", llvm_util::target_cpu(self.sess)));
 
         match self.sess.opts.cg.lto {
             config::Lto::Thin |
diff --git a/src/librustc_codegen_llvm/back/write.rs b/src/librustc_codegen_llvm/back/write.rs
index 80e9965e39c..2373428d68c 100644
--- a/src/librustc_codegen_llvm/back/write.rs
+++ b/src/librustc_codegen_llvm/back/write.rs
@@ -25,6 +25,7 @@ use rustc::session::Session;
 use rustc::util::nodemap::FxHashMap;
 use time_graph::{self, TimeGraph, Timeline};
 use llvm::{self, DiagnosticInfo, PassManager, SMDiagnostic};
+use llvm_util;
 use {CodegenResults, ModuleSource, ModuleCodegen, CompiledModule, ModuleKind};
 use CrateInfo;
 use rustc::hir::def_id::{CrateNum, LOCAL_CRATE};
@@ -173,7 +174,7 @@ pub fn target_machine_factory(sess: &Session, find_features: bool)
     let singlethread = sess.target.target.options.singlethread;
 
     let triple = SmallCStr::new(&sess.target.target.llvm_target);
-    let cpu = SmallCStr::new(sess.target_cpu());
+    let cpu = SmallCStr::new(llvm_util::target_cpu(sess));
     let features = attributes::llvm_target_features(sess)
         .collect::<Vec<_>>()
         .join(",");
diff --git a/src/librustc_codegen_llvm/llvm/ffi.rs b/src/librustc_codegen_llvm/llvm/ffi.rs
index d3039a05b6d..51b0299e63f 100644
--- a/src/librustc_codegen_llvm/llvm/ffi.rs
+++ b/src/librustc_codegen_llvm/llvm/ffi.rs
@@ -1449,6 +1449,7 @@ extern "C" {
     pub fn LLVMRustPrintTargetCPUs(T: &TargetMachine);
     pub fn LLVMRustPrintTargetFeatures(T: &TargetMachine);
 
+    pub fn LLVMRustGetHostCPUName(len: *mut usize) -> *const c_char;
     pub fn LLVMRustCreateTargetMachine(Triple: *const c_char,
                                        CPU: *const c_char,
                                        Features: *const c_char,
diff --git a/src/librustc_codegen_llvm/llvm_util.rs b/src/librustc_codegen_llvm/llvm_util.rs
index ff26e0f35f0..9fcc33d82cf 100644
--- a/src/librustc_codegen_llvm/llvm_util.rs
+++ b/src/librustc_codegen_llvm/llvm_util.rs
@@ -17,6 +17,8 @@ use libc::c_int;
 use std::ffi::CString;
 use syntax::feature_gate::UnstableFeatures;
 
+use std::str;
+use std::slice;
 use std::sync::atomic::{AtomicBool, Ordering};
 use std::sync::Once;
 
@@ -262,3 +264,19 @@ pub(crate) fn print(req: PrintRequest, sess: &Session) {
         }
     }
 }
+
+pub fn target_cpu(sess: &Session) -> &str {
+    let name = match sess.opts.cg.target_cpu {
+        Some(ref s) => &**s,
+        None => &*sess.target.target.options.cpu
+    };
+    if name != "native" {
+        return name
+    }
+
+    unsafe {
+        let mut len = 0;
+        let ptr = llvm::LLVMRustGetHostCPUName(&mut len);
+        str::from_utf8(slice::from_raw_parts(ptr as *const u8, len)).unwrap()
+    }
+}
diff --git a/src/rustllvm/PassWrapper.cpp b/src/rustllvm/PassWrapper.cpp
index 46825efeee2..09befdaae37 100644
--- a/src/rustllvm/PassWrapper.cpp
+++ b/src/rustllvm/PassWrapper.cpp
@@ -359,6 +359,12 @@ extern "C" void LLVMRustPrintTargetFeatures(LLVMTargetMachineRef) {
 }
 #endif
 
+extern "C" const char* LLVMRustGetHostCPUName(size_t *len) {
+  StringRef Name = sys::getHostCPUName();
+  *len = Name.size();
+  return Name.data();
+}
+
 extern "C" LLVMTargetMachineRef LLVMRustCreateTargetMachine(
     const char *TripleStr, const char *CPU, const char *Feature,
     LLVMRustCodeModel RustCM, LLVMRustRelocMode RustReloc,
@@ -381,11 +387,6 @@ extern "C" LLVMTargetMachineRef LLVMRustCreateTargetMachine(
     return nullptr;
   }
 
-  StringRef RealCPU = CPU;
-  if (RealCPU == "native") {
-    RealCPU = sys::getHostCPUName();
-  }
-
   TargetOptions Options;
 
   Options.FloatABIType = FloatABI::Default;
@@ -417,7 +418,7 @@ extern "C" LLVMTargetMachineRef LLVMRustCreateTargetMachine(
   if (RustCM != LLVMRustCodeModel::None)
     CM = fromRust(RustCM);
   TargetMachine *TM = TheTarget->createTargetMachine(
-      Trip.getTriple(), RealCPU, Feature, Options, RM, CM, OptLevel);
+      Trip.getTriple(), CPU, Feature, Options, RM, CM, OptLevel);
   return wrap(TM);
 }
 
diff --git a/src/test/run-make-fulldeps/target-cpu-native/Makefile b/src/test/run-make-fulldeps/target-cpu-native/Makefile
index 0c9d93ecb2a..fee41461612 100644
--- a/src/test/run-make-fulldeps/target-cpu-native/Makefile
+++ b/src/test/run-make-fulldeps/target-cpu-native/Makefile
@@ -1,5 +1,20 @@
 -include ../tools.mk
 
-all:
-	$(RUSTC) foo.rs -C target-cpu=native
+# I *really* don't want to deal with a cross-platform way to compare file sizes,
+# tests in `make` sort of are awful
+ifeq ($(TARGET),x86_64-unknown-linux-gnu)
+all: $(TMPDIR)/out.log
+	# Make sure no warnings about "unknown CPU `native`" were emitted
+	if [ "$$(wc -c $(TMPDIR)/out.log | cut -d' ' -f 1)" = "0" ]; then \
+	  echo no warnings generated; \
+	else \
+	  exit 1; \
+	fi
+else
+all: $(TMPDIR)/out.log
+endif
+
+
+$(TMPDIR)/out.log:
+	$(RUSTC) foo.rs -C target-cpu=native 2>&1 | tee $(TMPDIR)/out.log
 	$(call RUN,foo)