Rollup merge of #136439 - yotamofek:pr/codegen-ssa-no-indexing, r=Noratrieb

Misc. `rustc_codegen_ssa` cleanups 🧹

Just a bunch of stuff I found while reading the crate's code.
Each commit can stand on its own.
Maybe r? `@Noratrieb` because I saw you did some similar cleanups on these files a while ago? (feel free to re-assign, I'm just guessing)

4 files changed, 95 insertions, 110 deletions

diff --git a/compiler/rustc_codegen_ssa/src/back/link.rs b/compiler/rustc_codegen_ssa/src/back/link.rs
index a8d917f0fdb..4c076450269 100644
--- a/compiler/rustc_codegen_ssa/src/back/link.rs
+++ b/compiler/rustc_codegen_ssa/src/back/link.rs
@@ -244,22 +244,17 @@ pub fn each_linked_rlib(
 
         fmts
     } else {
-        for combination in info.dependency_formats.iter().combinations(2) {
-            let (ty1, list1) = &combination[0];
-            let (ty2, list2) = &combination[1];
-            if list1 != list2 {
-                return Err(errors::LinkRlibError::IncompatibleDependencyFormats {
-                    ty1: format!("{ty1:?}"),
-                    ty2: format!("{ty2:?}"),
-                    list1: format!("{list1:?}"),
-                    list2: format!("{list2:?}"),
-                });
-            }
-        }
-        if info.dependency_formats.is_empty() {
-            return Err(errors::LinkRlibError::MissingFormat);
+        let mut dep_formats = info.dependency_formats.iter();
+        let (ty1, list1) = dep_formats.next().ok_or(errors::LinkRlibError::MissingFormat)?;
+        if let Some((ty2, list2)) = dep_formats.find(|(_, list2)| list1 != *list2) {
+            return Err(errors::LinkRlibError::IncompatibleDependencyFormats {
+                ty1: format!("{ty1:?}"),
+                ty2: format!("{ty2:?}"),
+                list1: format!("{list1:?}"),
+                list2: format!("{list2:?}"),
+            });
         }
-        info.dependency_formats.first().unwrap().1
+        list1
     };
 
     let used_dep_crates = info.used_crates.iter();
@@ -626,10 +621,9 @@ fn link_staticlib(
 
     let mut all_rust_dylibs = vec![];
     for &cnum in crates {
-        match fmts.get(cnum) {
-            Some(&Linkage::Dynamic) => {}
-            _ => continue,
-        }
+        let Some(Linkage::Dynamic) = fmts.get(cnum) else {
+            continue;
+        };
         let crate_name = codegen_results.crate_info.crate_name[&cnum];
         let used_crate_source = &codegen_results.crate_info.used_crate_source[&cnum];
         if let Some((path, _)) = &used_crate_source.dylib {
diff --git a/compiler/rustc_codegen_ssa/src/back/write.rs b/compiler/rustc_codegen_ssa/src/back/write.rs
index d2548deb8c7..f008bd12ed8 100644
--- a/compiler/rustc_codegen_ssa/src/back/write.rs
+++ b/compiler/rustc_codegen_ssa/src/back/write.rs
@@ -573,10 +573,10 @@ fn produce_final_output_artifacts(
     };
 
     let copy_if_one_unit = |output_type: OutputType, keep_numbered: bool| {
-        if compiled_modules.modules.len() == 1 {
+        if let [module] = &compiled_modules.modules[..] {
             // 1) Only one codegen unit. In this case it's no difficulty
             //    to copy `foo.0.x` to `foo.x`.
-            let module_name = Some(&compiled_modules.modules[0].name[..]);
+            let module_name = Some(&module.name[..]);
             let path = crate_output.temp_path(output_type, module_name);
             let output = crate_output.path(output_type);
             if !output_type.is_text_output() && output.is_tty() {
@@ -708,8 +708,8 @@ fn produce_final_output_artifacts(
     }
 
     if sess.opts.json_artifact_notifications {
-        if compiled_modules.modules.len() == 1 {
-            compiled_modules.modules[0].for_each_output(|_path, ty| {
+        if let [module] = &compiled_modules.modules[..] {
+            module.for_each_output(|_path, ty| {
                 if sess.opts.output_types.contains_key(&ty) {
                     let descr = ty.shorthand();
                     // for single cgu file is renamed to drop cgu specific suffix
@@ -865,7 +865,7 @@ pub(crate) fn compute_per_cgu_lto_type(
     // require LTO so the request for LTO is always unconditionally
     // passed down to the backend, but we don't actually want to do
     // anything about it yet until we've got a final product.
-    let is_rlib = sess_crate_types.len() == 1 && sess_crate_types[0] == CrateType::Rlib;
+    let is_rlib = matches!(sess_crate_types, [CrateType::Rlib]);
 
     match sess_lto {
         Lto::ThinLocal if !linker_does_lto && !is_allocator => ComputedLtoType::Thin,
@@ -1538,8 +1538,9 @@ fn start_executing_work<B: ExtraBackendMethods>(
             // Spin up what work we can, only doing this while we've got available
             // parallelism slots and work left to spawn.
             if codegen_state != Aborted {
-                while !work_items.is_empty() && running_with_own_token < tokens.len() {
-                    let (item, _) = work_items.pop().unwrap();
+                while running_with_own_token < tokens.len()
+                    && let Some((item, _)) = work_items.pop()
+                {
                     spawn_work(
                         &cgcx,
                         &mut llvm_start_time,
diff --git a/compiler/rustc_codegen_ssa/src/codegen_attrs.rs b/compiler/rustc_codegen_ssa/src/codegen_attrs.rs
index 286e5e17908..97bc84c0b69 100644
--- a/compiler/rustc_codegen_ssa/src/codegen_attrs.rs
+++ b/compiler/rustc_codegen_ssa/src/codegen_attrs.rs
@@ -1,7 +1,6 @@
 use std::str::FromStr;
 
 use rustc_abi::ExternAbi;
-use rustc_ast::attr::list_contains_name;
 use rustc_ast::expand::autodiff_attrs::{
     AutoDiffAttrs, DiffActivity, DiffMode, valid_input_activity, valid_ret_activity,
 };
@@ -377,24 +376,20 @@ fn codegen_fn_attrs(tcx: TyCtxt<'_>, did: LocalDefId) -> CodegenFnAttrs {
                             let segments =
                                 set.path.segments.iter().map(|x| x.ident.name).collect::<Vec<_>>();
                             match segments.as_slice() {
-                                [sym::arm, sym::a32] | [sym::arm, sym::t32] => {
-                                    if !tcx.sess.target.has_thumb_interworking {
-                                        struct_span_code_err!(
-                                            tcx.dcx(),
-                                            attr.span,
-                                            E0779,
-                                            "target does not support `#[instruction_set]`"
-                                        )
-                                        .emit();
-                                        None
-                                    } else if segments[1] == sym::a32 {
-                                        Some(InstructionSetAttr::ArmA32)
-                                    } else if segments[1] == sym::t32 {
-                                        Some(InstructionSetAttr::ArmT32)
-                                    } else {
-                                        unreachable!()
-                                    }
+                                [sym::arm, sym::a32 | sym::t32]
+                                    if !tcx.sess.target.has_thumb_interworking =>
+                                {
+                                    struct_span_code_err!(
+                                        tcx.dcx(),
+                                        attr.span,
+                                        E0779,
+                                        "target does not support `#[instruction_set]`"
+                                    )
+                                    .emit();
+                                    None
                                 }
+                                [sym::arm, sym::a32] => Some(InstructionSetAttr::ArmA32),
+                                [sym::arm, sym::t32] => Some(InstructionSetAttr::ArmT32),
                                 _ => {
                                     struct_span_code_err!(
                                         tcx.dcx(),
@@ -435,7 +430,7 @@ fn codegen_fn_attrs(tcx: TyCtxt<'_>, did: LocalDefId) -> CodegenFnAttrs {
                     && let Some((sym::align, literal)) = item.singleton_lit_list()
                 {
                     rustc_attr_parsing::parse_alignment(&literal.kind)
-                        .map_err(|msg| {
+                        .inspect_err(|msg| {
                             struct_span_code_err!(
                                 tcx.dcx(),
                                 literal.span,
@@ -536,25 +531,27 @@ fn codegen_fn_attrs(tcx: TyCtxt<'_>, did: LocalDefId) -> CodegenFnAttrs {
         }
 
         if attr.is_word() {
-            InlineAttr::Hint
-        } else if let Some(ref items) = attr.meta_item_list() {
-            inline_span = Some(attr.span);
-            if items.len() != 1 {
-                struct_span_code_err!(tcx.dcx(), attr.span, E0534, "expected one argument").emit();
-                InlineAttr::None
-            } else if list_contains_name(items, sym::always) {
-                InlineAttr::Always
-            } else if list_contains_name(items, sym::never) {
-                InlineAttr::Never
-            } else {
-                struct_span_code_err!(tcx.dcx(), items[0].span(), E0535, "invalid argument")
-                    .with_help("valid inline arguments are `always` and `never`")
-                    .emit();
+            return InlineAttr::Hint;
+        }
+        let Some(ref items) = attr.meta_item_list() else {
+            return ia;
+        };
 
-                InlineAttr::None
-            }
+        inline_span = Some(attr.span);
+        let [item] = &items[..] else {
+            struct_span_code_err!(tcx.dcx(), attr.span, E0534, "expected one argument").emit();
+            return InlineAttr::None;
+        };
+        if item.has_name(sym::always) {
+            InlineAttr::Always
+        } else if item.has_name(sym::never) {
+            InlineAttr::Never
         } else {
-            ia
+            struct_span_code_err!(tcx.dcx(), item.span(), E0535, "invalid argument")
+                .with_help("valid inline arguments are `always` and `never`")
+                .emit();
+
+            InlineAttr::None
         }
     });
     codegen_fn_attrs.inline = attrs.iter().fold(codegen_fn_attrs.inline, |ia, attr| {
@@ -586,23 +583,25 @@ fn codegen_fn_attrs(tcx: TyCtxt<'_>, did: LocalDefId) -> CodegenFnAttrs {
         let err = |sp, s| struct_span_code_err!(tcx.dcx(), sp, E0722, "{}", s).emit();
         if attr.is_word() {
             err(attr.span, "expected one argument");
-            ia
-        } else if let Some(ref items) = attr.meta_item_list() {
-            inline_span = Some(attr.span);
-            if items.len() != 1 {
-                err(attr.span, "expected one argument");
-                OptimizeAttr::Default
-            } else if list_contains_name(items, sym::size) {
-                OptimizeAttr::Size
-            } else if list_contains_name(items, sym::speed) {
-                OptimizeAttr::Speed
-            } else if list_contains_name(items, sym::none) {
-                OptimizeAttr::DoNotOptimize
-            } else {
-                err(items[0].span(), "invalid argument");
-                OptimizeAttr::Default
-            }
+            return ia;
+        }
+        let Some(ref items) = attr.meta_item_list() else {
+            return OptimizeAttr::Default;
+        };
+
+        inline_span = Some(attr.span);
+        let [item] = &items[..] else {
+            err(attr.span, "expected one argument");
+            return OptimizeAttr::Default;
+        };
+        if item.has_name(sym::size) {
+            OptimizeAttr::Size
+        } else if item.has_name(sym::speed) {
+            OptimizeAttr::Speed
+        } else if item.has_name(sym::none) {
+            OptimizeAttr::DoNotOptimize
         } else {
+            err(item.span(), "invalid argument");
             OptimizeAttr::Default
         }
     });
@@ -644,25 +643,20 @@ fn codegen_fn_attrs(tcx: TyCtxt<'_>, did: LocalDefId) -> CodegenFnAttrs {
     // llvm/llvm-project#70563).
     if !codegen_fn_attrs.target_features.is_empty()
         && matches!(codegen_fn_attrs.inline, InlineAttr::Always)
+        && let Some(span) = inline_span
     {
-        if let Some(span) = inline_span {
-            tcx.dcx().span_err(span, "cannot use `#[inline(always)]` with `#[target_feature]`");
-        }
+        tcx.dcx().span_err(span, "cannot use `#[inline(always)]` with `#[target_feature]`");
     }
 
-    if !codegen_fn_attrs.no_sanitize.is_empty() && codegen_fn_attrs.inline.always() {
-        if let (Some(no_sanitize_span), Some(inline_span)) = (no_sanitize_span, inline_span) {
-            let hir_id = tcx.local_def_id_to_hir_id(did);
-            tcx.node_span_lint(
-                lint::builtin::INLINE_NO_SANITIZE,
-                hir_id,
-                no_sanitize_span,
-                |lint| {
-                    lint.primary_message("`no_sanitize` will have no effect after inlining");
-                    lint.span_note(inline_span, "inlining requested here");
-                },
-            )
-        }
+    if !codegen_fn_attrs.no_sanitize.is_empty()
+        && codegen_fn_attrs.inline.always()
+        && let (Some(no_sanitize_span), Some(inline_span)) = (no_sanitize_span, inline_span)
+    {
+        let hir_id = tcx.local_def_id_to_hir_id(did);
+        tcx.node_span_lint(lint::builtin::INLINE_NO_SANITIZE, hir_id, no_sanitize_span, |lint| {
+            lint.primary_message("`no_sanitize` will have no effect after inlining");
+            lint.span_note(inline_span, "inlining requested here");
+        })
     }
 
     // Weak lang items have the same semantics as "std internal" symbols in the
@@ -692,10 +686,10 @@ fn codegen_fn_attrs(tcx: TyCtxt<'_>, did: LocalDefId) -> CodegenFnAttrs {
     // Any linkage to LLVM intrinsics for now forcibly marks them all as never
     // unwinds since LLVM sometimes can't handle codegen which `invoke`s
     // intrinsic functions.
-    if let Some(name) = &codegen_fn_attrs.link_name {
-        if name.as_str().starts_with("llvm.") {
-            codegen_fn_attrs.flags |= CodegenFnAttrFlags::NEVER_UNWIND;
-        }
+    if let Some(name) = &codegen_fn_attrs.link_name
+        && name.as_str().starts_with("llvm.")
+    {
+        codegen_fn_attrs.flags |= CodegenFnAttrFlags::NEVER_UNWIND;
     }
 
     if let Some(features) = check_tied_features(
@@ -756,18 +750,13 @@ fn should_inherit_track_caller(tcx: TyCtxt<'_>, def_id: DefId) -> bool {
 
 fn check_link_ordinal(tcx: TyCtxt<'_>, attr: &hir::Attribute) -> Option<u16> {
     use rustc_ast::{LitIntType, LitKind, MetaItemLit};
-    let meta_item_list = attr.meta_item_list();
-    let meta_item_list = meta_item_list.as_deref();
-    let sole_meta_list = match meta_item_list {
-        Some([item]) => item.lit(),
-        Some(_) => {
-            tcx.dcx().emit_err(errors::InvalidLinkOrdinalNargs { span: attr.span });
-            return None;
-        }
-        _ => None,
+    let meta_item_list = attr.meta_item_list()?;
+    let [sole_meta_list] = &meta_item_list[..] else {
+        tcx.dcx().emit_err(errors::InvalidLinkOrdinalNargs { span: attr.span });
+        return None;
     };
     if let Some(MetaItemLit { kind: LitKind::Int(ordinal, LitIntType::Unsuffixed), .. }) =
-        sole_meta_list
+        sole_meta_list.lit()
     {
         // According to the table at
         // https://docs.microsoft.com/en-us/windows/win32/debug/pe-format#import-header, the
diff --git a/compiler/rustc_codegen_ssa/src/mir/block.rs b/compiler/rustc_codegen_ssa/src/mir/block.rs
index 676a241c74b..1e52c639463 100644
--- a/compiler/rustc_codegen_ssa/src/mir/block.rs
+++ b/compiler/rustc_codegen_ssa/src/mir/block.rs
@@ -1003,8 +1003,9 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
         let destination = target.map(|target| (return_dest, target));
 
         // Split the rust-call tupled arguments off.
-        let (first_args, untuple) = if abi == ExternAbi::RustCall && !args.is_empty() {
-            let (tup, args) = args.split_last().unwrap();
+        let (first_args, untuple) = if abi == ExternAbi::RustCall
+            && let Some((tup, args)) = args.split_last()
+        {
             (args, Some(tup))
         } else {
             (args, None)