Auto merge of #88575 - eddyb:fn-abi-queries, r=nagisa

Querify `FnAbi::of_{fn_ptr,instance}` as `fn_abi_of_{fn_ptr,instance}`.

*Note: opening this PR as draft because it's based on #88499*

This more or less replicates the `LayoutOf::layout_of` setup from #88499, to replace `FnAbi::of_{fn_ptr,instance}` with `FnAbiOf::fn_abi_of_{fn_ptr,instance}`, and also route them through queries (which `layout_of` has used for a while).

The two changes at the use sites (other than the names) are:
* return type is now wrapped in `&'tcx`
  * the value *is* interned, which may affect performance
* the `extra_args` list is now an interned `&'tcx ty::List<Ty<'tcx>>`
  * should be cheap (it's empty for anything other than C variadics)

Theoretically, a `FnAbiOfHelpers` implementer could choose to keep the `Result<...>` instead of eagerly erroring, but the only existing users of these APIs are codegen backends, so they don't (want to) take advantage of this.
At least miri could make use of this, since it prefers propagating errors (it "just" doesn't use `FnAbi` yet - cc `@RalfJung).`

The way this is done is probably less efficient than what is possible, because the queries handle the correctness-oriented API (i.e. the split into `fn` pointers vs instances), whereas a lower-level query could end up with more reuse between different instances with identical signatures.

r? `@nagisa` cc `@oli-obk` `@bjorn3`

1 files changed, 47 insertions, 5 deletions

diff --git a/compiler/rustc_codegen_llvm/src/context.rs b/compiler/rustc_codegen_llvm/src/context.rs
index 2d397dc5835..52a12b2fd81 100644
--- a/compiler/rustc_codegen_llvm/src/context.rs
+++ b/compiler/rustc_codegen_llvm/src/context.rs
@@ -15,14 +15,19 @@ use rustc_data_structures::base_n;
 use rustc_data_structures::fx::FxHashMap;
 use rustc_data_structures::small_c_str::SmallCStr;
 use rustc_middle::mir::mono::CodegenUnit;
-use rustc_middle::ty::layout::{HasParamEnv, LayoutError, LayoutOfHelpers, TyAndLayout};
+use rustc_middle::ty::layout::{
+    FnAbiError, FnAbiOfHelpers, FnAbiRequest, HasParamEnv, LayoutError, LayoutOfHelpers,
+    TyAndLayout,
+};
 use rustc_middle::ty::{self, Instance, Ty, TyCtxt};
 use rustc_middle::{bug, span_bug};
 use rustc_session::config::{CFGuard, CrateType, DebugInfo};
 use rustc_session::Session;
 use rustc_span::source_map::Span;
 use rustc_span::symbol::Symbol;
-use rustc_target::abi::{HasDataLayout, PointeeInfo, Size, TargetDataLayout, VariantIdx};
+use rustc_target::abi::{
+    call::FnAbi, HasDataLayout, PointeeInfo, Size, TargetDataLayout, VariantIdx,
+};
 use rustc_target::spec::{HasTargetSpec, RelocModel, Target, TlsModel};
 use smallvec::SmallVec;
 
@@ -835,6 +840,12 @@ impl ty::layout::HasTyCtxt<'tcx> for CodegenCx<'ll, 'tcx> {
     }
 }
 
+impl<'tcx, 'll> HasParamEnv<'tcx> for CodegenCx<'ll, 'tcx> {
+    fn param_env(&self) -> ty::ParamEnv<'tcx> {
+        ty::ParamEnv::reveal_all()
+    }
+}
+
 impl LayoutOfHelpers<'tcx> for CodegenCx<'ll, 'tcx> {
     type LayoutOfResult = TyAndLayout<'tcx>;
 
@@ -848,8 +859,39 @@ impl LayoutOfHelpers<'tcx> for CodegenCx<'ll, 'tcx> {
     }
 }
 
-impl<'tcx, 'll> HasParamEnv<'tcx> for CodegenCx<'ll, 'tcx> {
-    fn param_env(&self) -> ty::ParamEnv<'tcx> {
-        ty::ParamEnv::reveal_all()
+impl FnAbiOfHelpers<'tcx> for CodegenCx<'ll, 'tcx> {
+    type FnAbiOfResult = &'tcx FnAbi<'tcx, Ty<'tcx>>;
+
+    #[inline]
+    fn handle_fn_abi_err(
+        &self,
+        err: FnAbiError<'tcx>,
+        span: Span,
+        fn_abi_request: FnAbiRequest<'tcx>,
+    ) -> ! {
+        if let FnAbiError::Layout(LayoutError::SizeOverflow(_)) = err {
+            self.sess().span_fatal(span, &err.to_string())
+        } else {
+            match fn_abi_request {
+                FnAbiRequest::OfFnPtr { sig, extra_args } => {
+                    span_bug!(
+                        span,
+                        "`fn_abi_of_fn_ptr({}, {:?})` failed: {}",
+                        sig,
+                        extra_args,
+                        err
+                    );
+                }
+                FnAbiRequest::OfInstance { instance, extra_args } => {
+                    span_bug!(
+                        span,
+                        "`fn_abi_of_instance({}, {:?})` failed: {}",
+                        instance,
+                        extra_args,
+                        err
+                    );
+                }
+            }
+        }
     }
 }