Require backends to opt into implementing an intrinsic that has a fallback body

Author: oli-obk

compiler/rustc_codegen_cranelift/src/intrinsics/mod.rs

@@ -443,12 +443,6 @@ fn codegen_regular_intrinsic_call<'tcx>(
 
             ret.write_cvalue(fx, a);
         }
-        sym::is_val_statically_known => {
-            intrinsic_args!(fx, args => (_a); intrinsic);
-
-            let res = fx.bcx.ins().iconst(types::I8, 0);
-            ret.write_cvalue(fx, CValue::by_val(res, ret.layout()));
-        }
         sym::breakpoint => {
             intrinsic_args!(fx, args => (); intrinsic);
 

compiler/rustc_codegen_cranelift/src/lib.rs

@@ -248,6 +248,10 @@ impl CodegenBackend for CraneliftCodegenBackend {
 
         link_binary(sess, &crate::archive::ArArchiveBuilderBuilder, &codegen_results, outputs)
     }
+
+    fn implemented_intrinsics(&self) -> &'static [Symbol] {
+        &[]
+    }
 }
 
 fn target_triple(sess: &Session) -> target_lexicon::Triple {

compiler/rustc_codegen_gcc/src/lib.rs

@@ -110,6 +110,7 @@ use rustc_session::Session;
 use rustc_span::Symbol;
 use rustc_span::fatal_error::FatalError;
 use tempfile::TempDir;
+use rustc_span::sym;
 
 use crate::back::lto::ModuleBuffer;
 use crate::gcc_util::target_cpu;
@@ -242,6 +243,10 @@ impl CodegenBackend for GccCodegenBackend {
     fn target_features(&self, sess: &Session, allow_unstable: bool) -> Vec<Symbol> {
         target_features(sess, allow_unstable, &self.target_info)
     }
+
+    fn implemented_intrinsics(&self) -> &'static [Symbol] {
+        &[sym::is_val_statically_known]
+    }
 }
 
 fn new_context<'gcc, 'tcx>(tcx: TyCtxt<'tcx>) -> Context<'gcc> {

compiler/rustc_codegen_llvm/src/lib.rs

@@ -44,6 +44,7 @@ use rustc_middle::ty::TyCtxt;
 use rustc_middle::util::Providers;
 use rustc_session::config::{OptLevel, OutputFilenames, PrintKind, PrintRequest};
 use rustc_session::Session;
+use rustc_span::sym;
 use rustc_span::symbol::Symbol;
 
 use std::any::Any;
@@ -401,6 +402,10 @@ impl CodegenBackend for LlvmCodegenBackend {
         // This should produce either a finished executable or library.
         link_binary(sess, &LlvmArchiveBuilderBuilder, &codegen_results, outputs)
     }
+
+    fn implemented_intrinsics(&self) -> &'static [Symbol] {
+        &[sym::is_val_statically_known]
+    }
 }
 
 pub struct ModuleLlvm {

compiler/rustc_codegen_ssa/src/traits/backend.rs

@@ -111,6 +111,9 @@ pub trait CodegenBackend {
         codegen_results: CodegenResults,
         outputs: &OutputFilenames,
     ) -> Result<(), ErrorGuaranteed>;
+
+    /// Returns the list of intrinsics that should not use their fallback body
+    fn implemented_intrinsics(&self) -> &'static [Symbol];
 }
 
 pub trait ExtraBackendMethods:

compiler/rustc_interface/src/queries.rs

@@ -165,6 +165,9 @@ impl<'tcx> Queries<'tcx> {
                 feed.crate_name(crate_name);
 
                 let feed = tcx.feed_unit_query();
+                feed.intrinsics_implemented_by_backend(
+                    self.compiler.codegen_backend.implemented_intrinsics(),
+                );
                 feed.features_query(tcx.arena.alloc(rustc_expand::config::features(
                     sess,
                     &pre_configured_attrs,

compiler/rustc_middle/src/query/mod.rs

@@ -2105,6 +2105,11 @@ rustc_queries! {
         desc { "looking up enabled feature gates" }
     }
 
+    query intrinsics_implemented_by_backend(_: ()) -> &'static [Symbol] {
+        feedable
+        desc { "list of intrinsics with default bodies supported by the codegen backend" }
+    }
+
     query crate_for_resolver((): ()) -> &'tcx Steal<(rustc_ast::Crate, rustc_ast::AttrVec)> {
         feedable
         no_hash

compiler/rustc_middle/src/ty/util.rs

@@ -1544,12 +1544,12 @@ pub fn intrinsic(tcx: TyCtxt<'_>, def_id: LocalDefId) -> Option<Symbol> {
     {
         Some(tcx.item_name(def_id.into()))
     } else if let Some(name) = tcx.get_attr(def_id, sym::rustc_intrinsic) {
-        Some(
+        let name =
             name.get_normal_item().meta(rustc_span::DUMMY_SP).unwrap().meta_item_list().unwrap()[0]
                 .ident()
                 .unwrap()
-                .name,
-        )
+                .name;
+        tcx.intrinsics_implemented_by_backend(()).contains(&name).then_some(name)
     } else {
         None
     }

tests/run-make-fulldeps/hotplug_codegen_backend/the_backend.rs

@@ -27,7 +27,9 @@ use std::any::Any;
 struct TheBackend;
 
 impl CodegenBackend for TheBackend {
-    fn locale_resource(&self) -> &'static str { "" }
+    fn locale_resource(&self) -> &'static str {
+        ""
+    }
 
     fn codegen_crate<'a, 'tcx>(
         &self,
@@ -62,7 +64,10 @@ impl CodegenBackend for TheBackend {
         codegen_results: CodegenResults,
         outputs: &OutputFilenames,
     ) -> Result<(), ErrorGuaranteed> {
-        use rustc_session::{config::{CrateType, OutFileName}, output::out_filename};
+        use rustc_session::{
+            config::{CrateType, OutFileName},
+            output::out_filename,
+        };
         use std::io::Write;
         let crate_name = codegen_results.crate_info.local_crate_name;
         for &crate_type in sess.opts.crate_types.iter() {
@@ -83,6 +88,10 @@ impl CodegenBackend for TheBackend {
         }
         Ok(())
     }
+
+    fn implemented_intrinsics(&self) -> &'static [Symbol] {
+        &[]
+    }
 }
 
 /// This is the entrypoint for a hot plugged rustc_codegen_llvm