Auto merge of rust-lang#130679 - saethlin:inline-usually, r=<try>

Add inline(usually)

r? `@ghost`

I'm looking into what kind of things could recover the perf improvement detected in rust-lang#121417 (comment)

Author: bors

compiler/rustc_attr/src/builtin.rs

@@ -46,6 +46,7 @@ pub enum InlineAttr {
     Hint,
     Always,
     Never,
+    Usually,
 }
 
 #[derive(Clone, Encodable, Decodable, Debug, PartialEq, Eq, HashStable_Generic)]

compiler/rustc_codegen_gcc/src/attributes.rs

@@ -30,6 +30,7 @@ fn inline_attr<'gcc, 'tcx>(
                 None
             }
         }
+        InlineAttr::Usually => Some(FnAttribute::Inline),
         InlineAttr::None => None,
     }
 }

compiler/rustc_codegen_llvm/src/attributes.rs

@@ -47,6 +47,9 @@ fn inline_attr<'ll>(cx: &CodegenCx<'ll, '_>, inline: InlineAttr) -> Option<&'ll
             }
         }
         InlineAttr::None => None,
+        InlineAttr::Usually => {
+            Some(llvm::CreateAttrStringValue(cx.llcx, "function-inline-cost", "0"))
+        }
     }
 }
 

compiler/rustc_codegen_ssa/src/codegen_attrs.rs

@@ -525,9 +525,15 @@ fn codegen_fn_attrs(tcx: TyCtxt<'_>, did: LocalDefId) -> CodegenFnAttrs {
                         .emit();
                     InlineAttr::None
                 } else if list_contains_name(items, sym::always) {
-                    InlineAttr::Always
+                    if tcx.sess.opts.optimize == rustc_session::config::OptLevel::No {
+                        InlineAttr::Usually
+                    } else {
+                        InlineAttr::Always
+                    }
                 } else if list_contains_name(items, sym::never) {
                     InlineAttr::Never
+                } else if list_contains_name(items, sym::usually) {
+                    InlineAttr::Usually
                 } else {
                     struct_span_code_err!(tcx.dcx(), items[0].span(), E0535, "invalid argument")
                         .with_help("valid inline arguments are `always` and `never`")

compiler/rustc_mir_transform/src/cross_crate_inline.rs

@@ -46,7 +46,7 @@ fn cross_crate_inlinable(tcx: TyCtxt<'_>, def_id: LocalDefId) -> bool {
     // #[inline(never)] to force code generation.
     match codegen_fn_attrs.inline {
         InlineAttr::Never => return false,
-        InlineAttr::Hint | InlineAttr::Always => return true,
+        InlineAttr::Hint | InlineAttr::Always | InlineAttr::Usually => return true,
         _ => {}
     }
 

compiler/rustc_mir_transform/src/inline.rs

@@ -106,7 +106,7 @@ fn inline<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) -> bool {
         changed: false,
         caller_is_inline_forwarder: matches!(
             codegen_fn_attrs.inline,
-            InlineAttr::Hint | InlineAttr::Always
+            InlineAttr::Hint | InlineAttr::Always | InlineAttr::Usually
         ) && body_is_forwarder(body),
     };
     let blocks = START_BLOCK..body.basic_blocks.next_index();

compiler/rustc_span/src/symbol.rs

@@ -2102,6 +2102,7 @@ symbols! {
         usize_legacy_fn_max_value,
         usize_legacy_fn_min_value,
         usize_legacy_mod,
+        usually,
         va_arg,
         va_copy,
         va_end,