2 files changed, 76 insertions, 7 deletions

diff --git a/compiler/rustc_codegen_llvm/src/llvm/ffi.rs b/compiler/rustc_codegen_llvm/src/llvm/ffi.rs
index 70f78c07c65..54a8249b175 100644
--- a/compiler/rustc_codegen_llvm/src/llvm/ffi.rs
+++ b/compiler/rustc_codegen_llvm/src/llvm/ffi.rs
@@ -2128,7 +2128,13 @@ extern "C" {
     pub fn LLVMRustHasFeature(T: &TargetMachine, s: *const c_char) -> bool;
 
     pub fn LLVMRustPrintTargetCPUs(T: &TargetMachine);
-    pub fn LLVMRustPrintTargetFeatures(T: &TargetMachine);
+    pub fn LLVMRustGetTargetFeaturesCount(T: &TargetMachine) -> size_t;
+    pub fn LLVMRustGetTargetFeature(
+        T: &TargetMachine,
+        Index: size_t,
+        Feature: &mut *const c_char,
+        Desc: &mut *const c_char,
+    );
 
     pub fn LLVMRustGetHostCPUName(len: *mut usize) -> *const c_char;
     pub fn LLVMRustCreateTargetMachine(
diff --git a/compiler/rustc_codegen_llvm/src/llvm_util.rs b/compiler/rustc_codegen_llvm/src/llvm_util.rs
index e80de2bc902..b44553e4f6d 100644
--- a/compiler/rustc_codegen_llvm/src/llvm_util.rs
+++ b/compiler/rustc_codegen_llvm/src/llvm_util.rs
@@ -10,6 +10,7 @@ use rustc_span::symbol::Symbol;
 use rustc_target::spec::{MergeFunctions, PanicStrategy};
 use std::ffi::{CStr, CString};
 
+use std::ptr;
 use std::slice;
 use std::str;
 use std::sync::atomic::{AtomicBool, Ordering};
@@ -192,15 +193,77 @@ pub fn print_passes() {
     }
 }
 
+fn llvm_target_features(tm: &llvm::TargetMachine) -> Vec<(&str, &str)> {
+    let len = unsafe { llvm::LLVMRustGetTargetFeaturesCount(tm) };
+    let mut ret = Vec::with_capacity(len);
+    for i in 0..len {
+        unsafe {
+            let mut feature = ptr::null();
+            let mut desc = ptr::null();
+            llvm::LLVMRustGetTargetFeature(tm, i, &mut feature, &mut desc);
+            if feature.is_null() || desc.is_null() {
+                bug!("LLVM returned a `null` target feature string");
+            }
+            let feature = CStr::from_ptr(feature).to_str().unwrap_or_else(|e| {
+                bug!("LLVM returned a non-utf8 feature string: {}", e);
+            });
+            let desc = CStr::from_ptr(desc).to_str().unwrap_or_else(|e| {
+                bug!("LLVM returned a non-utf8 feature string: {}", e);
+            });
+            ret.push((feature, desc));
+        }
+    }
+    ret
+}
+
+fn print_target_features(sess: &Session, tm: &llvm::TargetMachine) {
+    let mut target_features = llvm_target_features(tm);
+    let mut rustc_target_features = supported_target_features(sess)
+        .iter()
+        .filter_map(|(feature, _gate)| {
+            let llvm_feature = to_llvm_feature(sess, *feature);
+            // LLVM asserts that these are sorted. LLVM and Rust both use byte comparison for these strings.
+            target_features.binary_search_by_key(&llvm_feature, |(f, _d)| *f).ok().map(|index| {
+                let (_f, desc) = target_features.remove(index);
+                (*feature, desc)
+            })
+        })
+        .collect::<Vec<_>>();
+    rustc_target_features.extend_from_slice(&[(
+        "crt-static",
+        "Enables C Run-time Libraries to be statically linked",
+    )]);
+    let max_feature_len = target_features
+        .iter()
+        .chain(rustc_target_features.iter())
+        .map(|(feature, _desc)| feature.len())
+        .max()
+        .unwrap_or(0);
+
+    println!("Features supported by rustc for this target:");
+    for (feature, desc) in &rustc_target_features {
+        println!("    {1:0$} - {2}.", max_feature_len, feature, desc);
+    }
+    println!("\nCode-generation features supported by LLVM for this target:");
+    for (feature, desc) in &target_features {
+        println!("    {1:0$} - {2}.", max_feature_len, feature, desc);
+    }
+    if target_features.len() == 0 {
+        println!("    Target features listing is not supported by this LLVM version.");
+    }
+    println!("\nUse +feature to enable a feature, or -feature to disable it.");
+    println!("For example, rustc -C target-cpu=mycpu -C target-feature=+feature1,-feature2\n");
+    println!("Code-generation features cannot be used in cfg or #[target_feature],");
+    println!("and may be renamed or removed in a future version of LLVM or rustc.\n");
+}
+
 pub(crate) fn print(req: PrintRequest, sess: &Session) {
     require_inited();
     let tm = create_informational_target_machine(sess);
-    unsafe {
-        match req {
-            PrintRequest::TargetCPUs => llvm::LLVMRustPrintTargetCPUs(tm),
-            PrintRequest::TargetFeatures => llvm::LLVMRustPrintTargetFeatures(tm),
-            _ => bug!("rustc_codegen_llvm can't handle print request: {:?}", req),
-        }
+    match req {
+        PrintRequest::TargetCPUs => unsafe { llvm::LLVMRustPrintTargetCPUs(tm) },
+        PrintRequest::TargetFeatures => print_target_features(sess, tm),
+        _ => bug!("rustc_codegen_llvm can't handle print request: {:?}", req),
     }
 }