rustc/driver: improve/remove allocations

Author: ljedrz

src/librustc_driver/driver.rs

@@ -1586,9 +1586,8 @@ pub fn collect_crate_types(session: &Session, attrs: &[ast::Attribute]) -> Vec<c
         base.dedup();
     }
 
-    base.into_iter()
-        .filter(|crate_type| {
-            let res = !::rustc_codegen_utils::link::invalid_output_for_target(session, *crate_type);
+    base.retain(|crate_type| {
+        let res = !::rustc_codegen_utils::link::invalid_output_for_target(session, *crate_type);
 
             if !res {
                 session.warn(&format!(
@@ -1597,9 +1596,10 @@ pub fn collect_crate_types(session: &Session, attrs: &[ast::Attribute]) -> Vec<c
                 ));
             }
 
-            res
-        })
-        .collect()
+        res
+    });
+
+    base
 }
 
 pub fn compute_crate_disambiguator(session: &Session) -> CrateDisambiguator {

src/librustc_driver/lib.rs

@@ -137,9 +137,7 @@ pub mod target_features {
                              codegen_backend: &dyn CodegenBackend) {
         let tf = Symbol::intern("target_feature");
 
-        for feat in codegen_backend.target_features(sess) {
-            cfg.insert((tf, Some(feat)));
-        }
+        cfg.extend(codegen_backend.target_features(sess).into_iter().map(|feat| (tf, Some(feat))));
 
         if sess.crt_static_feature() {
             cfg.insert((tf, Some(Symbol::intern("crt-static"))));
@@ -997,7 +995,7 @@ impl RustcDefaultCalls {
                          input: &Input)
                          -> Compilation {
         let r = matches.opt_strs("Z");
-        if r.contains(&("ls".to_string())) {
+        if r.iter().any(|s| *s == "ls") {
             match input {
                 &Input::File(ref ifile) => {
                     let path = &(*ifile);
@@ -1085,8 +1083,7 @@ impl RustcDefaultCalls {
                     let allow_unstable_cfg = UnstableFeatures::from_environment()
                         .is_nightly_build();
 
-                    let mut cfgs = Vec::new();
-                    for &(name, ref value) in sess.parse_sess.config.iter() {
+                    let mut cfgs = sess.parse_sess.config.iter().filter_map(|&(name, ref value)| {
                         let gated_cfg = GatedCfg::gate(&ast::MetaItem {
                             ident: ast::Path::from_ident(ast::Ident::with_empty_ctxt(name)),
                             node: ast::MetaItemKind::Word,
@@ -1105,16 +1102,16 @@ impl RustcDefaultCalls {
                         let value = value.as_ref().map(|s| s.as_ref());
                         if name != "target_feature" || value != Some("crt-static") {
                             if !allow_unstable_cfg && gated_cfg.is_some() {
-                                continue;
+                                return None
                             }
                         }
 
-                        cfgs.push(if let Some(value) = value {
-                            format!("{}=\"{}\"", name, value)
+                        if let Some(value) = value {
+                            Some(format!("{}=\"{}\"", name, value))
                         } else {
-                            name.to_string()
-                        });
-                    }
+                            Some(name.to_string())
+                        }
+                    }).collect::<Vec<String>>();
 
                     cfgs.sort();
                     for cfg in cfgs {
@@ -1177,7 +1174,7 @@ fn usage(verbose: bool, include_unstable_options: bool) {
     for option in groups.iter().filter(|x| include_unstable_options || x.is_stable()) {
         (option.apply)(&mut options);
     }
-    let message = "Usage: rustc [OPTIONS] INPUT".to_string();
+    let message = "Usage: rustc [OPTIONS] INPUT";
     let nightly_help = if nightly_options::is_nightly_build() {
         "\n    -Z help             Print internal options for debugging rustc"
     } else {
@@ -1192,7 +1189,7 @@ fn usage(verbose: bool, include_unstable_options: bool) {
     -C help             Print codegen options
     -W help             \
               Print 'lint' options and default settings{}{}\n",
-             options.usage(&message),
+             options.usage(message),
              nightly_help,
              verbose_help);
 }
@@ -1463,7 +1460,7 @@ pub fn handle_options(args: &[String]) -> Option<getopts::Matches> {
                    "the --no-stack-check flag is deprecated and does nothing");
     }
 
-    if cg_flags.contains(&"passes=list".to_string()) {
+    if cg_flags.iter().any(|x| *x == "passes=list") {
         get_codegen_sysroot("llvm")().print_passes();
         return None;
     }

src/librustc_driver/profile/trace.rs

@@ -89,18 +89,18 @@ fn html_of_duration(_start: &Instant, dur: &Duration) -> (String, String) {
     )
 }
 
-fn html_of_fraction(frac: f64) -> (String, String) {
+fn html_of_fraction(frac: f64) -> (String, &'static str) {
     let css = {
-        if       frac > 0.50  { "frac-50".to_string() }
-        else if  frac > 0.40  { "frac-40".to_string() }
-        else if  frac > 0.30  { "frac-30".to_string() }
-        else if  frac > 0.20  { "frac-20".to_string() }
-        else if  frac > 0.10  { "frac-10".to_string() }
-        else if  frac > 0.05  { "frac-05".to_string() }
-        else if  frac > 0.02  { "frac-02".to_string() }
-        else if  frac > 0.01  { "frac-01".to_string() }
-        else if  frac > 0.001 { "frac-001".to_string() }
-        else                  { "frac-0".to_string() }
+        if       frac > 0.50  { "frac-50" }
+        else if  frac > 0.40  { "frac-40" }
+        else if  frac > 0.30  { "frac-30" }
+        else if  frac > 0.20  { "frac-20" }
+        else if  frac > 0.10  { "frac-10" }
+        else if  frac > 0.05  { "frac-05" }
+        else if  frac > 0.02  { "frac-02" }
+        else if  frac > 0.01  { "frac-01" }
+        else if  frac > 0.001 { "frac-001" }
+        else                  { "frac-0" }
     };
     let percent = frac * 100.0;
     if percent > 0.1 { (format!("{:.1}%", percent), css) }
@@ -148,6 +148,7 @@ fn write_traces_rec(file: &mut File, traces: &[Rec], total: Duration, depth: usi
 }
 
 fn compute_counts_rec(counts: &mut FxHashMap<String,QueryMetric>, traces: &[Rec]) {
+    counts.reserve(traces.len());
     for t in traces.iter() {
         match t.effect {
             Effect::TimeBegin(ref msg) => {