Implement a dependant target feature mechanism

Author: daxpedda

compiler/rustc_codegen_llvm/src/llvm_util.rs

@@ -654,6 +654,12 @@ pub(crate) fn global_llvm_features(sess: &Session, diagnostics: bool) -> Vec<Str
         });
     }
 
+    for (feature, requires) in sess.target.dependant_target_features() {
+        if features.iter().any(|f| f == feature) && !features.iter().any(|f| f == requires) {
+            features.push(format!("+{requires}"));
+        }
+    }
+
     features
 }
 

compiler/rustc_codegen_ssa/src/target_features.rs

@@ -96,6 +96,12 @@ pub fn from_target_feature(
             Some(Symbol::intern(feature))
         }));
     }
+
+    for (feature, requires) in tcx.sess.target.dependant_target_features() {
+        if target_features.iter().any(|f| f.as_str() == *feature) && !target_features.iter().any(|f| f.as_str() == *requires) {
+            target_features.push(Symbol::intern(requires));
+        }
+    }
 }
 
 /// Computes the set of target features used in a function for the purposes of

compiler/rustc_target/src/target_features.rs

@@ -336,6 +336,8 @@ const WASM_ALLOWED_FEATURES: &[(&str, Stability)] = &[
     // tidy-alphabetical-end
 ];
 
+const WASM_DEPENDANT_FEATURES: &[(&str, &str)] = &[("relaxed-simd", "simd128")];
+
 const BPF_ALLOWED_FEATURES: &[(&str, Stability)] = &[("alu32", Unstable(sym::bpf_target_feature))];
 
 const CSKY_ALLOWED_FEATURES: &[(&str, Stability)] = &[
@@ -452,4 +454,12 @@ impl super::spec::Target {
             _ => &[],
         }
     }
+
+    /// Returns a list of target features. Each items first target feature requires the second one.
+    pub fn dependant_target_features(&self) -> &'static [(&'static str, &'static str)] {
+        match &*self.arch {
+            "wasm32" | "wasm64" => WASM_DEPENDANT_FEATURES,
+            _ => &[],
+        }
+    }
 }

tests/ui/target-feature/dependant-features-cli.rs

@@ -0,0 +1,9 @@
+//@ only-wasm32-wasip1
+//@ compile-flags: -Ctarget-feature=+relaxed-simd --crate-type=lib
+//@ build-pass
+
+use std::arch::wasm32::*;
+
+pub fn test(a: v128, b: v128, m: v128) -> v128 {
+    i64x2_relaxed_laneselect(a, b, m)
+}

tests/ui/target-feature/dependant-features.rs

@@ -0,0 +1,10 @@
+//@ only-wasm32-wasip1
+//@ compile-flags: --crate-type=lib
+//@ build-pass
+
+use std::arch::wasm32::*;
+
+#[target_feature(enable = "relaxed-simd")]
+pub fn test(a: v128, b: v128, m: v128) -> v128 {
+    i64x2_relaxed_laneselect(a, b, m)
+}

tests/ui/target-feature/wasm-relaxed-simd.rs

@@ -1,5 +1,5 @@
 //@ only-wasm32-wasip1
-//@ compile-flags: -Ctarget-feature=+relaxed-simd,+simd128 --crate-type=lib
+//@ compile-flags: -Ctarget-feature=+relaxed-simd --crate-type=lib
 //@ build-pass
 
 use std::arch::wasm32::*;