From f4e1ac42a70653fe0fbeb62fb25f1c9395c9e63b Mon Sep 17 00:00:00 2001
From: kulst <kulst@mailbox.org>
Date: Wed, 5 Feb 2025 21:33:58 +0100
Subject: [PATCH] Pass through of target features to llvm-bitcode-linker and
 handling them

The .ptx version produced by llc can be specified by passing it with --mattr. Currently it is not possible to specify the .ptx version with -Ctarget-feature because these are not passed through to llvm-bitcode-linker and handled by it. This commit adds both.
--target-feature and -mattr are passed with equals to mitigate issues when the value starts with a - (minus).
---
 compiler/rustc_codegen_ssa/src/back/link.rs         |  6 ++++++
 src/tools/llvm-bitcode-linker/Cargo.toml            |  2 +-
 .../src/bin/llvm-bitcode-linker.rs                  |  6 +++++-
 src/tools/llvm-bitcode-linker/src/linker.rs         | 13 ++++++++++++-
 4 files changed, 24 insertions(+), 3 deletions(-)

diff --git a/compiler/rustc_codegen_ssa/src/back/link.rs b/compiler/rustc_codegen_ssa/src/back/link.rs
index 105a4cb81f0d1..a6bff951ab188 100644
--- a/compiler/rustc_codegen_ssa/src/back/link.rs
+++ b/compiler/rustc_codegen_ssa/src/back/link.rs
@@ -2518,6 +2518,12 @@ fn add_order_independent_options(
             "--target-cpu",
             &codegen_results.crate_info.target_cpu,
         ]);
+        if let Some(feat) = [sess.opts.cg.target_feature.as_str(), &sess.target.options.features]
+            .into_iter()
+            .find(|feat| !feat.is_empty())
+        {
+            cmd.link_arg(&format!("--target-feature={}", feat));
+        }
     } else if flavor == LinkerFlavor::Ptx {
         cmd.link_args(&["--fallback-arch", &codegen_results.crate_info.target_cpu]);
     } else if flavor == LinkerFlavor::Bpf {
diff --git a/src/tools/llvm-bitcode-linker/Cargo.toml b/src/tools/llvm-bitcode-linker/Cargo.toml
index a9210b562f330..f4afee19ca05c 100644
--- a/src/tools/llvm-bitcode-linker/Cargo.toml
+++ b/src/tools/llvm-bitcode-linker/Cargo.toml
@@ -1,6 +1,6 @@
 [package]
 name = "llvm-bitcode-linker"
-version = "0.0.1"
+version = "0.0.2"
 description = "A self-contained linker for llvm bitcode"
 license = "MIT OR Apache-2.0"
 edition = "2021"
diff --git a/src/tools/llvm-bitcode-linker/src/bin/llvm-bitcode-linker.rs b/src/tools/llvm-bitcode-linker/src/bin/llvm-bitcode-linker.rs
index fdbf6171c53f2..608c6605304f4 100644
--- a/src/tools/llvm-bitcode-linker/src/bin/llvm-bitcode-linker.rs
+++ b/src/tools/llvm-bitcode-linker/src/bin/llvm-bitcode-linker.rs
@@ -27,6 +27,10 @@ pub struct Args {
     #[arg(long)]
     target_cpu: Option<String>,
 
+    /// The target features
+    #[arg(long)]
+    target_feature: Option<String>,
+
     /// Write output to the filename
     #[arg(short, long)]
     output: PathBuf,
@@ -49,7 +53,7 @@ fn main() -> anyhow::Result<()> {
 
     let args = Args::parse();
 
-    let mut linker = Session::new(args.target, args.target_cpu, args.output);
+    let mut linker = Session::new(args.target, args.target_cpu, args.target_feature, args.output);
 
     linker.add_exported_symbols(args.export_symbol);
 
diff --git a/src/tools/llvm-bitcode-linker/src/linker.rs b/src/tools/llvm-bitcode-linker/src/linker.rs
index 9f579d1009408..7d294c53b6e78 100644
--- a/src/tools/llvm-bitcode-linker/src/linker.rs
+++ b/src/tools/llvm-bitcode-linker/src/linker.rs
@@ -8,6 +8,7 @@ use crate::{Optimization, Target};
 pub struct Session {
     target: Target,
     cpu: Option<String>,
+    feature: Option<String>,
     symbols: Vec<String>,
 
     /// A file that `llvm-link` supports, like a bitcode file or an archive.
@@ -21,7 +22,12 @@ pub struct Session {
 }
 
 impl Session {
-    pub fn new(target: crate::Target, cpu: Option<String>, out_path: PathBuf) -> Self {
+    pub fn new(
+        target: crate::Target,
+        cpu: Option<String>,
+        feature: Option<String>,
+        out_path: PathBuf,
+    ) -> Self {
         let link_path = out_path.with_extension("o");
         let opt_path = out_path.with_extension("optimized.o");
         let sym_path = out_path.with_extension("symbols.txt");
@@ -29,6 +35,7 @@ impl Session {
         Session {
             target,
             cpu,
+            feature,
             symbols: Vec::new(),
             files: Vec::new(),
             link_path,
@@ -134,6 +141,10 @@ impl Session {
             lcc_command.arg("--mcpu").arg(mcpu);
         }
 
+        if let Some(mattr) = &self.feature {
+            lcc_command.arg(&format!("-mattr={}", mattr));
+        }
+
         let lcc_output = lcc_command
             .arg(&self.opt_path)
             .arg("-o").arg(&self.out_path)