Auto merge of #88337 - eddyb:field-failure-is-not-an-option, r=nagisa

rustc_target: `TyAndLayout::field` should never error.

This refactor (making `TyAndLayout::field` return `TyAndLayout` without any `Result` around it) is based on a simple observation, regarding `TyAndLayout::field`:

If `cx.layout_of(ty)` succeeds (for some `cx` and `ty`), then `.field(cx, i)` on the resulting `TyAndLayout` should *always* succeed in computing `cx.layout_of(field_ty)` (where `field_ty` is the type of the `i`th field of `ty`).

The reason for this is that no matter which field is chosen, `cx.layout_of(field_ty)` *will have already been computed*, as part of computing `cx.layout_of(ty)`, as we cannot determine the layout of *any* type without considering the layouts of *all* of its fields.

And so it should be fine to turn any errors into ICEs, since they likely indicate a `cx` mismatch, or some other edge case that is due to a compiler bug (as opposed to ever being an user-facing error).

<hr/>

Each commit should probably be reviewed separately, though note that there's some `where` clauses (in `rustc_target::abi::call::*`) that change in most commits.

cc `@nagisa` `@oli-obk`

3 files changed, 7 insertions, 4 deletions

diff --git a/compiler/rustc_codegen_llvm/src/builder.rs b/compiler/rustc_codegen_llvm/src/builder.rs
index 13538683e05..47529f719b5 100644
--- a/compiler/rustc_codegen_llvm/src/builder.rs
+++ b/compiler/rustc_codegen_llvm/src/builder.rs
@@ -88,7 +88,7 @@ impl HasTargetSpec for Builder<'_, '_, 'tcx> {
     }
 }
 
-impl abi::LayoutOf for Builder<'_, '_, 'tcx> {
+impl abi::LayoutOf<'tcx> for Builder<'_, '_, 'tcx> {
     type Ty = Ty<'tcx>;
     type TyAndLayout = TyAndLayout<'tcx>;
 
diff --git a/compiler/rustc_codegen_llvm/src/context.rs b/compiler/rustc_codegen_llvm/src/context.rs
index 35c866d48a4..45da18d4a24 100644
--- a/compiler/rustc_codegen_llvm/src/context.rs
+++ b/compiler/rustc_codegen_llvm/src/context.rs
@@ -835,7 +835,7 @@ impl ty::layout::HasTyCtxt<'tcx> for CodegenCx<'ll, 'tcx> {
     }
 }
 
-impl LayoutOf for CodegenCx<'ll, 'tcx> {
+impl LayoutOf<'tcx> for CodegenCx<'ll, 'tcx> {
     type Ty = Ty<'tcx>;
     type TyAndLayout = TyAndLayout<'tcx>;
 
diff --git a/compiler/rustc_codegen_llvm/src/type_of.rs b/compiler/rustc_codegen_llvm/src/type_of.rs
index 85efe3e6483..9818905464d 100644
--- a/compiler/rustc_codegen_llvm/src/type_of.rs
+++ b/compiler/rustc_codegen_llvm/src/type_of.rs
@@ -9,7 +9,7 @@ use rustc_middle::ty::print::with_no_trimmed_paths;
 use rustc_middle::ty::{self, Ty, TypeFoldable};
 use rustc_target::abi::{Abi, AddressSpace, Align, FieldsShape};
 use rustc_target::abi::{Int, Pointer, F32, F64};
-use rustc_target::abi::{LayoutOf, PointeeInfo, Scalar, Size, TyAndLayoutMethods, Variants};
+use rustc_target::abi::{LayoutOf, PointeeInfo, Scalar, Size, TyAbiInterface, Variants};
 use smallvec::{smallvec, SmallVec};
 use tracing::debug;
 
@@ -393,12 +393,15 @@ impl<'tcx> LayoutLlvmExt<'tcx> for TyAndLayout<'tcx> {
         }
     }
 
+    // FIXME(eddyb) this having the same name as `TyAndLayout::pointee_info_at`
+    // (the inherent method, which is lacking this caching logic) can result in
+    // the uncached version being called - not wrong, but potentially inefficient.
     fn pointee_info_at<'a>(&self, cx: &CodegenCx<'a, 'tcx>, offset: Size) -> Option<PointeeInfo> {
         if let Some(&pointee) = cx.pointee_infos.borrow().get(&(self.ty, offset)) {
             return pointee;
         }
 
-        let result = Ty::pointee_info_at(*self, cx, offset);
+        let result = Ty::ty_and_layout_pointee_info_at(*self, cx, offset);
 
         cx.pointee_infos.borrow_mut().insert((self.ty, offset), result);
         result