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, 41 insertions, 0 deletions

diff --git a/compiler/rustc_mir_transform/src/errors.rs b/compiler/rustc_mir_transform/src/errors.rs
index ad9635aae33..775f5f9a7cf 100644
--- a/compiler/rustc_mir_transform/src/errors.rs
+++ b/compiler/rustc_mir_transform/src/errors.rs
@@ -2,6 +2,7 @@ use rustc_errors::codes::*;
 use rustc_errors::{Diag, LintDiagnostic};
 use rustc_macros::{Diagnostic, LintDiagnostic, Subdiagnostic};
 use rustc_middle::mir::AssertKind;
+use rustc_middle::query::Key;
 use rustc_middle::ty::TyCtxt;
 use rustc_session::lint::{self, Lint};
 use rustc_span::def_id::DefId;
@@ -9,6 +10,46 @@ use rustc_span::{Ident, Span, Symbol};
 
 use crate::fluent_generated as fluent;
 
+/// Emit diagnostic for calls to `#[inline(always)]`-annotated functions with a
+/// `#[target_feature]` attribute where the caller enables a different set of target features.
+pub(crate) fn emit_inline_always_target_feature_diagnostic<'a, 'tcx>(
+    tcx: TyCtxt<'tcx>,
+    call_span: Span,
+    callee_def_id: DefId,
+    caller_def_id: DefId,
+    callee_only: &[&'a str],
+) {
+    let callee = tcx.def_path_str(callee_def_id);
+    let caller = tcx.def_path_str(caller_def_id);
+
+    tcx.node_span_lint(
+        lint::builtin::INLINE_ALWAYS_MISMATCHING_TARGET_FEATURES,
+        tcx.local_def_id_to_hir_id(caller_def_id.as_local().unwrap()),
+        call_span,
+        |lint| {
+            lint.primary_message(format!(
+                "call to `#[inline(always)]`-annotated `{callee}` \
+                requires the same target features to be inlined"
+            ));
+            lint.note("function will not be inlined");
+
+            lint.note(format!(
+                "the following target features are on `{callee}` but missing from `{caller}`: {}",
+                callee_only.join(", ")
+            ));
+            lint.span_note(callee_def_id.default_span(tcx), format!("`{callee}` is defined here"));
+
+            let feats = callee_only.join(",");
+            lint.span_suggestion(
+                tcx.def_span(caller_def_id).shrink_to_lo(),
+                format!("add `#[target_feature]` attribute to `{caller}`"),
+                format!("#[target_feature(enable = \"{feats}\")]\n"),
+                lint::Applicability::MaybeIncorrect,
+            );
+        },
+    );
+}
+
 #[derive(LintDiagnostic)]
 #[diag(mir_transform_unconditional_recursion)]
 #[help]