Rollup merge of #145932 - JamieCunliffe:target-feature-inlining, r=jackh726

Allow `inline(always)` with a target feature behind a unstable feature `target_feature_inline_always`.

Rather than adding the inline always attribute to the function definition, we add it to the callsite. We can then check that the target features match and that the call would be safe to inline. If the function isn't inlined due to a mismatch, we emit a warning informing the user that the function can't be inlined due to the target feature mismatch.

See tracking issue rust-lang/rust#145574

1 files changed, 21 insertions, 10 deletions

diff --git a/compiler/rustc_codegen_llvm/src/attributes.rs b/compiler/rustc_codegen_llvm/src/attributes.rs
index 5affb26483a..9f2d37d39d8 100644
--- a/compiler/rustc_codegen_llvm/src/attributes.rs
+++ b/compiler/rustc_codegen_llvm/src/attributes.rs
@@ -29,8 +29,18 @@ pub(crate) fn apply_to_callsite(callsite: &Value, idx: AttributePlace, attrs: &[
 }
 
 /// Get LLVM attribute for the provided inline heuristic.
-#[inline]
-fn inline_attr<'ll>(cx: &CodegenCx<'ll, '_>, inline: InlineAttr) -> Option<&'ll Attribute> {
+pub(crate) fn inline_attr<'ll, 'tcx>(
+    cx: &CodegenCx<'ll, 'tcx>,
+    instance: ty::Instance<'tcx>,
+) -> Option<&'ll Attribute> {
+    // `optnone` requires `noinline`
+    let codegen_fn_attrs = cx.tcx.codegen_fn_attrs(instance.def_id());
+    let inline = match (codegen_fn_attrs.inline, &codegen_fn_attrs.optimize) {
+        (_, OptimizeAttr::DoNotOptimize) => InlineAttr::Never,
+        (InlineAttr::None, _) if instance.def.requires_inline(cx.tcx) => InlineAttr::Hint,
+        (inline, _) => inline,
+    };
+
     if !cx.tcx.sess.opts.unstable_opts.inline_llvm {
         // disable LLVM inlining
         return Some(AttributeKind::NoInline.create_attr(cx.llcx));
@@ -346,14 +356,6 @@ pub(crate) fn llfn_attrs_from_instance<'ll, 'tcx>(
         OptimizeAttr::Speed => {}
     }
 
-    // `optnone` requires `noinline`
-    let inline = match (codegen_fn_attrs.inline, &codegen_fn_attrs.optimize) {
-        (_, OptimizeAttr::DoNotOptimize) => InlineAttr::Never,
-        (InlineAttr::None, _) if instance.def.requires_inline(cx.tcx) => InlineAttr::Hint,
-        (inline, _) => inline,
-    };
-    to_add.extend(inline_attr(cx, inline));
-
     if cx.sess().must_emit_unwind_tables() {
         to_add.push(uwtable_attr(cx.llcx, cx.sess().opts.unstable_opts.use_sync_unwind));
     }
@@ -488,6 +490,14 @@ pub(crate) fn llfn_attrs_from_instance<'ll, 'tcx>(
     let function_features =
         codegen_fn_attrs.target_features.iter().map(|f| f.name.as_str()).collect::<Vec<&str>>();
 
+    // Apply function attributes as per usual if there are no user defined
+    // target features otherwise this will get applied at the callsite.
+    if function_features.is_empty() {
+        if let Some(inline_attr) = inline_attr(cx, instance) {
+            to_add.push(inline_attr);
+        }
+    }
+
     let function_features = function_features
         .iter()
         // Convert to LLVMFeatures and filter out unavailable ones
@@ -517,6 +527,7 @@ pub(crate) fn llfn_attrs_from_instance<'ll, 'tcx>(
     let function_features = function_features.iter().map(|s| s.as_str());
     let target_features: String =
         global_features.chain(function_features).intersperse(",").collect();
+
     if !target_features.is_empty() {
         to_add.push(llvm::CreateAttrStringValue(cx.llcx, "target-features", &target_features));
     }