Auto merge of #120500 - oli-obk:intrinsics2.0, r=WaffleLapkin

Implement intrinsics with fallback bodies

fixes #93145 (though we can port many more intrinsics)
cc #63585

The way this works is that the backend logic for generating custom code for intrinsics has been made fallible. The only failure path is "this intrinsic is unknown". The `Instance` (that was `InstanceDef::Intrinsic`) then gets converted to `InstanceDef::Item`, which represents the fallback body. A regular function call to that body is then codegenned. This is currently implemented for

* codegen_ssa (so llvm and gcc)
* codegen_cranelift

other backends will need to adjust, but they can just keep doing what they were doing if they prefer (though adding new intrinsics to the compiler will then require them to implement them, instead of getting the fallback body).

cc `@scottmcm` `@WaffleLapkin`

### todo

* [ ] miri support
* [x] default intrinsic name to name of function instead of requiring it to be specified in attribute
* [x] make sure that the bodies are always available (must be collected for metadata)

1 files changed, 10 insertions, 8 deletions

diff --git a/compiler/rustc_codegen_gcc/src/intrinsic/mod.rs b/compiler/rustc_codegen_gcc/src/intrinsic/mod.rs
index eac8cb43779..f162ef831b7 100644
--- a/compiler/rustc_codegen_gcc/src/intrinsic/mod.rs
+++ b/compiler/rustc_codegen_gcc/src/intrinsic/mod.rs
@@ -90,7 +90,7 @@ fn get_simple_intrinsic<'gcc, 'tcx>(cx: &CodegenCx<'gcc, 'tcx>, name: Symbol) ->
 }
 
 impl<'a, 'gcc, 'tcx> IntrinsicCallMethods<'tcx> for Builder<'a, 'gcc, 'tcx> {
-    fn codegen_intrinsic_call(&mut self, instance: Instance<'tcx>, fn_abi: &FnAbi<'tcx, Ty<'tcx>>, args: &[OperandRef<'tcx, RValue<'gcc>>], llresult: RValue<'gcc>, span: Span) {
+    fn codegen_intrinsic_call(&mut self, instance: Instance<'tcx>, fn_abi: &FnAbi<'tcx, Ty<'tcx>>, args: &[OperandRef<'tcx, RValue<'gcc>>], llresult: RValue<'gcc>, span: Span) -> Result<(), Instance<'tcx>> {
         let tcx = self.tcx;
         let callee_ty = instance.ty(tcx, ty::ParamEnv::reveal_all());
 
@@ -137,7 +137,7 @@ impl<'a, 'gcc, 'tcx> IntrinsicCallMethods<'tcx> for Builder<'a, 'gcc, 'tcx> {
                         args[2].immediate(),
                         llresult,
                     );
-                    return;
+                    return Ok(());
                 }
                 sym::breakpoint => {
                     unimplemented!();
@@ -166,12 +166,12 @@ impl<'a, 'gcc, 'tcx> IntrinsicCallMethods<'tcx> for Builder<'a, 'gcc, 'tcx> {
                 sym::volatile_store => {
                     let dst = args[0].deref(self.cx());
                     args[1].val.volatile_store(self, dst);
-                    return;
+                    return Ok(());
                 }
                 sym::unaligned_volatile_store => {
                     let dst = args[0].deref(self.cx());
                     args[1].val.unaligned_volatile_store(self, dst);
-                    return;
+                    return Ok(());
                 }
                 sym::prefetch_read_data
                     | sym::prefetch_write_data
@@ -269,7 +269,7 @@ impl<'a, 'gcc, 'tcx> IntrinsicCallMethods<'tcx> for Builder<'a, 'gcc, 'tcx> {
                             },
                             None => {
                                 tcx.dcx().emit_err(InvalidMonomorphization::BasicIntegerType { span, name, ty });
-                                return;
+                                return Ok(());
                             }
                         }
                     }
@@ -339,7 +339,7 @@ impl<'a, 'gcc, 'tcx> IntrinsicCallMethods<'tcx> for Builder<'a, 'gcc, 'tcx> {
                     extended_asm.set_volatile_flag(true);
 
                     // We have copied the value to `result` already.
-                    return;
+                    return Ok(());
                 }
 
                 sym::ptr_mask => {
@@ -357,11 +357,12 @@ impl<'a, 'gcc, 'tcx> IntrinsicCallMethods<'tcx> for Builder<'a, 'gcc, 'tcx> {
                 _ if name_str.starts_with("simd_") => {
                     match generic_simd_intrinsic(self, name, callee_ty, args, ret_ty, llret_ty, span) {
                         Ok(llval) => llval,
-                        Err(()) => return,
+                        Err(()) => return Ok(()),
                     }
                 }
 
-                _ => bug!("unknown intrinsic '{}'", name),
+                // Fall back to default body
+                _ => return Err(Instance::new(instance.def_id(), instance.args)),
             };
 
         if !fn_abi.ret.is_ignore() {
@@ -376,6 +377,7 @@ impl<'a, 'gcc, 'tcx> IntrinsicCallMethods<'tcx> for Builder<'a, 'gcc, 'tcx> {
                     .store(self, result);
             }
         }
+        Ok(())
     }
 
     fn abort(&mut self) {