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)

2 files changed, 21 insertions, 26 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,