Pass +forced-atomics feature for riscv32{i,im,imc}-unknown-none-elf

Author: taiki-e

compiler/rustc_codegen_llvm/src/llvm_util.rs

@@ -507,6 +507,8 @@ pub(crate) fn global_llvm_features(sess: &Session, diagnostics: bool) -> Vec<Str
             .features
             .split(',')
             .filter(|v| !v.is_empty() && backend_feature_name(v).is_some())
+            // Drop +forced-atomics feature introduced in LLVM 16.
+            .filter(|v| *v != "+forced-atomics" || get_version() >= (16, 0, 0))
             .map(String::from),
     );
 

compiler/rustc_target/src/spec/targets/riscv32i_unknown_none_elf.rs

@@ -11,8 +11,9 @@ pub fn target() -> Target {
             linker_flavor: LinkerFlavor::Gnu(Cc::No, Lld::Yes),
             linker: Some("rust-lld".into()),
             cpu: "generic-rv32".into(),
-            max_atomic_width: Some(0),
+            max_atomic_width: Some(32),
             atomic_cas: false,
+            features: "+forced-atomics".into(),
             panic_strategy: PanicStrategy::Abort,
             relocation_model: RelocModel::Static,
             emit_debug_gdb_scripts: false,

compiler/rustc_target/src/spec/targets/riscv32im_unknown_none_elf.rs

@@ -11,9 +11,9 @@ pub fn target() -> Target {
             linker_flavor: LinkerFlavor::Gnu(Cc::No, Lld::Yes),
             linker: Some("rust-lld".into()),
             cpu: "generic-rv32".into(),
-            max_atomic_width: Some(0),
+            max_atomic_width: Some(32),
             atomic_cas: false,
-            features: "+m".into(),
+            features: "+m,+forced-atomics".into(),
             panic_strategy: PanicStrategy::Abort,
             relocation_model: RelocModel::Static,
             emit_debug_gdb_scripts: false,

compiler/rustc_target/src/spec/targets/riscv32imc_unknown_none_elf.rs

@@ -11,9 +11,9 @@ pub fn target() -> Target {
             linker_flavor: LinkerFlavor::Gnu(Cc::No, Lld::Yes),
             linker: Some("rust-lld".into()),
             cpu: "generic-rv32".into(),
-            max_atomic_width: Some(0),
+            max_atomic_width: Some(32),
             atomic_cas: false,
-            features: "+m,+c".into(),
+            features: "+m,+c,+forced-atomics".into(),
             panic_strategy: PanicStrategy::Abort,
             relocation_model: RelocModel::Static,
             emit_debug_gdb_scripts: false,