Rollup merge of #95202 - Urgau:check-cfg-perf-well-known-values, r=petrochenkov

Reduce the cost of loading all built-ins targets

This PR started by measuring the exact slowdown of checking of well known conditional values.
Than this PR implemented some technics to reduce the cost of loading all built-ins targets.

cf. https://github.com/rust-lang/rust/issues/82450#issuecomment-1073992323

3 files changed, 20 insertions, 19 deletions

diff --git a/compiler/rustc_codegen_ssa/src/back/link.rs b/compiler/rustc_codegen_ssa/src/back/link.rs
index 548ae0e411d..84a1043a6a0 100644
--- a/compiler/rustc_codegen_ssa/src/back/link.rs
+++ b/compiler/rustc_codegen_ssa/src/back/link.rs
@@ -40,6 +40,7 @@ use std::ffi::OsString;
 use std::fs::{File, OpenOptions};
 use std::io::{BufWriter, Write};
 use std::lazy::OnceCell;
+use std::ops::Deref;
 use std::path::{Path, PathBuf};
 use std::process::{ExitStatus, Output, Stdio};
 use std::{ascii, char, env, fmt, fs, io, mem, str};
@@ -674,11 +675,11 @@ fn link_natively<'a, B: ArchiveBuilder<'a>>(
 
     linker::disable_localization(&mut cmd);
 
-    for &(ref k, ref v) in &sess.target.link_env {
-        cmd.env(k, v);
+    for &(ref k, ref v) in sess.target.link_env.as_ref() {
+        cmd.env(k.as_ref(), v.as_ref());
     }
-    for k in &sess.target.link_env_remove {
-        cmd.env_remove(k);
+    for k in sess.target.link_env_remove.as_ref() {
+        cmd.env_remove(k.as_ref());
     }
 
     if sess.opts.prints.contains(&PrintRequest::LinkArgs) {
@@ -1216,7 +1217,7 @@ pub fn linker_and_flavor(sess: &Session) -> (PathBuf, LinkerFlavor) {
 
     if let Some(ret) = infer_from(
         sess,
-        sess.target.linker.clone().map(PathBuf::from),
+        sess.target.linker.as_deref().map(PathBuf::from),
         Some(sess.target.linker_flavor),
     ) {
         return ret;
@@ -1586,7 +1587,7 @@ fn add_post_link_objects(
 /// FIXME: Determine where exactly these args need to be inserted.
 fn add_pre_link_args(cmd: &mut dyn Linker, sess: &Session, flavor: LinkerFlavor) {
     if let Some(args) = sess.target.pre_link_args.get(&flavor) {
-        cmd.args(args);
+        cmd.args(args.iter().map(Deref::deref));
     }
     cmd.args(&sess.opts.debugging_opts.pre_link_args);
 }
@@ -1602,7 +1603,7 @@ fn add_link_script(cmd: &mut dyn Linker, sess: &Session, tmpdir: &Path, crate_ty
             let file_name = ["rustc", &sess.target.llvm_target, "linkfile.ld"].join("-");
 
             let path = tmpdir.join(file_name);
-            if let Err(e) = fs::write(&path, script) {
+            if let Err(e) = fs::write(&path, script.as_ref()) {
                 sess.fatal(&format!("failed to write link script to {}: {}", path.display(), e));
             }
 
@@ -1634,15 +1635,15 @@ fn add_late_link_args(
         });
     if any_dynamic_crate {
         if let Some(args) = sess.target.late_link_args_dynamic.get(&flavor) {
-            cmd.args(args);
+            cmd.args(args.iter().map(Deref::deref));
         }
     } else {
         if let Some(args) = sess.target.late_link_args_static.get(&flavor) {
-            cmd.args(args);
+            cmd.args(args.iter().map(Deref::deref));
         }
     }
     if let Some(args) = sess.target.late_link_args.get(&flavor) {
-        cmd.args(args);
+        cmd.args(args.iter().map(Deref::deref));
     }
 }
 
@@ -1650,7 +1651,7 @@ fn add_late_link_args(
 /// FIXME: Determine where exactly these args need to be inserted.
 fn add_post_link_args(cmd: &mut dyn Linker, sess: &Session, flavor: LinkerFlavor) {
     if let Some(args) = sess.target.post_link_args.get(&flavor) {
-        cmd.args(args);
+        cmd.args(args.iter().map(Deref::deref));
     }
 }
 
@@ -1960,8 +1961,8 @@ fn add_order_independent_options(
         cmd.arg(&codegen_results.crate_info.target_cpu);
         cmd.arg("--cpu-features");
         cmd.arg(match &sess.opts.cg.target_feature {
-            feat if !feat.is_empty() => feat,
-            _ => &sess.target.options.features,
+            feat if !feat.is_empty() => feat.as_ref(),
+            _ => sess.target.options.features.as_ref(),
         });
     }
 
@@ -2478,12 +2479,12 @@ fn add_apple_sdk(cmd: &mut dyn Linker, sess: &Session, flavor: LinkerFlavor) {
     let os = &sess.target.os;
     let llvm_target = &sess.target.llvm_target;
     if sess.target.vendor != "apple"
-        || !matches!(os.as_str(), "ios" | "tvos")
+        || !matches!(os.as_ref(), "ios" | "tvos")
         || flavor != LinkerFlavor::Gcc
     {
         return;
     }
-    let sdk_name = match (arch.as_str(), os.as_str()) {
+    let sdk_name = match (arch.as_ref(), os.as_ref()) {
         ("aarch64", "tvos") => "appletvos",
         ("x86_64", "tvos") => "appletvsimulator",
         ("arm", "ios") => "iphoneos",
diff --git a/compiler/rustc_codegen_ssa/src/back/linker.rs b/compiler/rustc_codegen_ssa/src/back/linker.rs
index 3a66bfafaf3..2c15ed83167 100644
--- a/compiler/rustc_codegen_ssa/src/back/linker.rs
+++ b/compiler/rustc_codegen_ssa/src/back/linker.rs
@@ -75,7 +75,7 @@ pub fn get_linker<'a>(
         if let Some(ref tool) = msvc_tool {
             let original_path = tool.path();
             if let Some(ref root_lib_path) = original_path.ancestors().nth(4) {
-                let arch = match t.arch.as_str() {
+                let arch = match t.arch.as_ref() {
                     "x86_64" => Some("x64"),
                     "x86" => Some("x86"),
                     "aarch64" => Some("arm64"),
@@ -1520,7 +1520,7 @@ impl<'a> L4Bender<'a> {
 
 pub(crate) fn exported_symbols(tcx: TyCtxt<'_>, crate_type: CrateType) -> Vec<String> {
     if let Some(ref exports) = tcx.sess.target.override_export_symbols {
-        return exports.clone();
+        return exports.iter().map(ToString::to_string).collect();
     }
 
     let mut symbols = Vec::new();
diff --git a/compiler/rustc_codegen_ssa/src/back/write.rs b/compiler/rustc_codegen_ssa/src/back/write.rs
index d4eaf6389df..9417874ffb4 100644
--- a/compiler/rustc_codegen_ssa/src/back/write.rs
+++ b/compiler/rustc_codegen_ssa/src/back/write.rs
@@ -218,7 +218,7 @@ impl ModuleConfig {
                 false
             ),
             emit_obj,
-            bc_cmdline: sess.target.bitcode_llvm_cmdline.clone(),
+            bc_cmdline: sess.target.bitcode_llvm_cmdline.to_string(),
 
             verify_llvm_ir: sess.verify_llvm_ir(),
             no_prepopulate_passes: sess.opts.cg.no_prepopulate_passes,
@@ -1061,7 +1061,7 @@ fn start_executing_work<B: ExtraBackendMethods>(
         is_pe_coff: tcx.sess.target.is_like_windows,
         target_can_use_split_dwarf: tcx.sess.target_can_use_split_dwarf(),
         target_pointer_width: tcx.sess.target.pointer_width,
-        target_arch: tcx.sess.target.arch.clone(),
+        target_arch: tcx.sess.target.arch.to_string(),
         debuginfo: tcx.sess.opts.debuginfo,
         split_debuginfo: tcx.sess.split_debuginfo(),
         split_dwarf_kind: tcx.sess.opts.debugging_opts.split_dwarf_kind,