Rollup merge of #128679 - RalfJung:codegen-fn-attrs, r=nikic

codegen: better centralize function declaration attribute computation

For some reason, the codegen backend has two functions that compute which attributes a function declaration gets: `apply_attrs_llfn` and `attributes::from_fn_attrs`. They are called in different places, on entirely different layers of abstraction.

To me the code seems cleaner if we centralize this entirely in `apply_attrs_llfn`, so that's what this PR does.

compiler/rustc_codegen_llvm/src/abi.rs

@@ -5,10 +5,10 @@ use rustc_codegen_ssa::mir::operand::{OperandRef, OperandValue};
 use rustc_codegen_ssa::mir::place::{PlaceRef, PlaceValue};
 use rustc_codegen_ssa::traits::*;
 use rustc_codegen_ssa::MemFlags;
-use rustc_middle::bug;
 use rustc_middle::ty::layout::LayoutOf;
 pub use rustc_middle::ty::layout::{FAT_PTR_ADDR, FAT_PTR_EXTRA};
 use rustc_middle::ty::Ty;
+use rustc_middle::{bug, ty};
 use rustc_session::config;
 pub use rustc_target::abi::call::*;
 use rustc_target::abi::{self, HasDataLayout, Int, Size};
@@ -16,6 +16,7 @@ pub use rustc_target::spec::abi::Abi;
 use rustc_target::spec::SanitizerSet;
 use smallvec::SmallVec;
 
+use crate::attributes::llfn_attrs_from_instance;
 use crate::builder::Builder;
 use crate::context::CodegenCx;
 use crate::llvm::{self, Attribute, AttributePlace};
@@ -310,7 +311,16 @@ pub trait FnAbiLlvmExt<'ll, 'tcx> {
     fn llvm_type(&self, cx: &CodegenCx<'ll, 'tcx>) -> &'ll Type;
     fn ptr_to_llvm_type(&self, cx: &CodegenCx<'ll, 'tcx>) -> &'ll Type;
     fn llvm_cconv(&self) -> llvm::CallConv;
-    fn apply_attrs_llfn(&self, cx: &CodegenCx<'ll, 'tcx>, llfn: &'ll Value);
+
+    /// Apply attributes to a function declaration/definition.
+    fn apply_attrs_llfn(
+        &self,
+        cx: &CodegenCx<'ll, 'tcx>,
+        llfn: &'ll Value,
+        instance: Option<ty::Instance<'tcx>>,
+    );
+
+    /// Apply attributes to a function call.
     fn apply_attrs_callsite(&self, bx: &mut Builder<'_, 'll, 'tcx>, callsite: &'ll Value);
 }
 
@@ -396,7 +406,12 @@ impl<'ll, 'tcx> FnAbiLlvmExt<'ll, 'tcx> for FnAbi<'tcx, Ty<'tcx>> {
         self.conv.into()
     }
 
-    fn apply_attrs_llfn(&self, cx: &CodegenCx<'ll, 'tcx>, llfn: &'ll Value) {
+    fn apply_attrs_llfn(
+        &self,
+        cx: &CodegenCx<'ll, 'tcx>,
+        llfn: &'ll Value,
+        instance: Option<ty::Instance<'tcx>>,
+    ) {
         let mut func_attrs = SmallVec::<[_; 3]>::new();
         if self.ret.layout.abi.is_uninhabited() {
             func_attrs.push(llvm::AttributeKind::NoReturn.create_attr(cx.llcx));
@@ -477,6 +492,11 @@ impl<'ll, 'tcx> FnAbiLlvmExt<'ll, 'tcx> for FnAbi<'tcx, Ty<'tcx>> {
                 }
             }
         }
+
+        // If the declaration has an associated instance, compute extra attributes based on that.
+        if let Some(instance) = instance {
+            llfn_attrs_from_instance(cx, llfn, instance);
+        }
     }
 
     fn apply_attrs_callsite(&self, bx: &mut Builder<'_, 'll, 'tcx>, callsite: &'ll Value) {

compiler/rustc_codegen_llvm/src/attributes.rs

@@ -324,9 +324,10 @@ fn create_alloc_family_attr(llcx: &llvm::Context) -> &llvm::Attribute {
     llvm::CreateAttrStringValue(llcx, "alloc-family", "__rust_alloc")
 }
 
+/// Helper for `FnAbi::apply_attrs_llfn`:
 /// Composite function which sets LLVM attributes for function depending on its AST (`#[attribute]`)
 /// attributes.
-pub fn from_fn_attrs<'ll, 'tcx>(
+pub fn llfn_attrs_from_instance<'ll, 'tcx>(
     cx: &CodegenCx<'ll, 'tcx>,
     llfn: &'ll Value,
     instance: ty::Instance<'tcx>,

compiler/rustc_codegen_llvm/src/callee.rs

@@ -10,8 +10,8 @@ use rustc_middle::ty::{self, Instance, TypeVisitableExt};
 use tracing::debug;
 
 use crate::context::CodegenCx;
+use crate::llvm;
 use crate::value::Value;
-use crate::{attributes, llvm};
 
 /// Codegens a reference to a fn/method item, monomorphizing and
 /// inlining as it goes.
@@ -78,8 +78,6 @@ pub fn get_fn<'ll, 'tcx>(cx: &CodegenCx<'ll, 'tcx>, instance: Instance<'tcx>) ->
         };
         debug!("get_fn: not casting pointer!");
 
-        attributes::from_fn_attrs(cx, llfn, instance);
-
         // Apply an appropriate linkage/visibility value to our item that we
         // just declared.
         //

compiler/rustc_codegen_llvm/src/declare.rs

@@ -137,7 +137,7 @@ impl<'ll, 'tcx> CodegenCx<'ll, 'tcx> {
             llvm::Visibility::Default,
             fn_abi.llvm_type(self),
         );
-        fn_abi.apply_attrs_llfn(self, llfn);
+        fn_abi.apply_attrs_llfn(self, llfn, instance);
 
         if self.tcx.sess.is_sanitizer_cfi_enabled() {
             if let Some(instance) = instance {

compiler/rustc_codegen_llvm/src/mono_item.rs

@@ -12,7 +12,7 @@ use tracing::debug;
 use crate::context::CodegenCx;
 use crate::errors::SymbolAlreadyDefined;
 use crate::type_of::LayoutLlvmExt;
-use crate::{attributes, base, llvm};
+use crate::{base, llvm};
 
 impl<'tcx> PreDefineMethods<'tcx> for CodegenCx<'_, 'tcx> {
     fn predefine_static(
@@ -87,8 +87,6 @@ impl<'tcx> PreDefineMethods<'tcx> for CodegenCx<'_, 'tcx> {
 
         debug!("predefine_fn: instance = {:?}", instance);
 
-        attributes::from_fn_attrs(self, lldecl, instance);
-
         unsafe {
             if self.should_assume_dso_local(lldecl, false) {
                 llvm::LLVMRustSetDSOLocal(lldecl, true);