Rollup merge of #135504 - veluca93:target-feature-cast-to-fn-ptr, r=oli-obk

Allow coercing safe-to-call target_feature functions to safe fn pointers

r? oli-obk

`@oli-obk:` this is based on your PR #134353 :-)

See https://github.com/rust-lang/rust/pull/134090#issuecomment-2539422624 for the motivation behind this change.

1 files changed, 32 insertions, 1 deletions

diff --git a/compiler/rustc_middle/src/ty/context.rs b/compiler/rustc_middle/src/ty/context.rs
index fab0047babf..7035e641f39 100644
--- a/compiler/rustc_middle/src/ty/context.rs
+++ b/compiler/rustc_middle/src/ty/context.rs
@@ -60,7 +60,7 @@ use crate::dep_graph::{DepGraph, DepKindStruct};
 use crate::infer::canonical::{CanonicalParamEnvCache, CanonicalVarInfo, CanonicalVarInfos};
 use crate::lint::lint_level;
 use crate::metadata::ModChild;
-use crate::middle::codegen_fn_attrs::CodegenFnAttrs;
+use crate::middle::codegen_fn_attrs::{CodegenFnAttrs, TargetFeature};
 use crate::middle::{resolve_bound_vars, stability};
 use crate::mir::interpret::{self, Allocation, ConstAllocation};
 use crate::mir::{Body, Local, Place, PlaceElem, ProjectionKind, Promoted};
@@ -1776,6 +1776,37 @@ impl<'tcx> TyCtxt<'tcx> {
     pub fn dcx(self) -> DiagCtxtHandle<'tcx> {
         self.sess.dcx()
     }
+
+    pub fn is_target_feature_call_safe(
+        self,
+        callee_features: &[TargetFeature],
+        body_features: &[TargetFeature],
+    ) -> bool {
+        // If the called function has target features the calling function hasn't,
+        // the call requires `unsafe`. Don't check this on wasm
+        // targets, though. For more information on wasm see the
+        // is_like_wasm check in hir_analysis/src/collect.rs
+        self.sess.target.options.is_like_wasm
+            || callee_features
+                .iter()
+                .all(|feature| body_features.iter().any(|f| f.name == feature.name))
+    }
+
+    /// Returns the safe version of the signature of the given function, if calling it
+    /// would be safe in the context of the given caller.
+    pub fn adjust_target_feature_sig(
+        self,
+        fun_def: DefId,
+        fun_sig: ty::Binder<'tcx, ty::FnSig<'tcx>>,
+        caller: DefId,
+    ) -> Option<ty::Binder<'tcx, ty::FnSig<'tcx>>> {
+        let fun_features = &self.codegen_fn_attrs(fun_def).target_features;
+        let callee_features = &self.codegen_fn_attrs(caller).target_features;
+        if self.is_target_feature_call_safe(&fun_features, &callee_features) {
+            return Some(fun_sig.map_bound(|sig| ty::FnSig { safety: hir::Safety::Safe, ..sig }));
+        }
+        None
+    }
 }
 
 impl<'tcx> TyCtxtAt<'tcx> {