Some optimizations

* Only format global _comments when debug_assertions are enabled
* Only call build_value_labels_ranges in base.rs when debug_assertions are enabled

Benchmark #1: CHANNEL='pre' ../cargo.sh build
  Time (mean ± σ):     17.657 s ±  1.050 s    [User: 31.871 s, System: 3.014 s]
  Range (min … max):   16.907 s … 20.394 s    10 runs

Benchmark #2: ../cargo.sh build
  Time (mean ± σ):     16.640 s ±  0.255 s    [User: 30.238 s, System: 2.965 s]
  Range (min … max):   16.413 s … 17.186 s    10 runs

  Warning: Statistical outliers were detected. Consider re-running this benchmark on a quiet PC without any interferences from other programs. It might help to use the '--warmup' or '--prepare' options.

Summary
  '../cargo.sh build' ran
    1.06 ± 0.07 times faster than 'CHANNEL='pre' ../cargo.sh build'

src/base.rs

@@ -74,20 +74,22 @@ pub fn trans_fn<'clif, 'tcx, B: Backend + 'static>(
     context.func = func;
     cx.module.define_function(func_id, context).unwrap();
 
-    let value_ranges = context
-        .build_value_labels_ranges(cx.module.isa())
-        .expect("value location ranges");
-
     // Write optimized function to file for debugging
     #[cfg(debug_assertions)]
-    crate::pretty_clif::write_clif_file(
-        cx.tcx,
-        "opt",
-        instance,
-        &context.func,
-        &clif_comments,
-        Some(&value_ranges),
-    );
+    {
+        let value_ranges = context
+            .build_value_labels_ranges(cx.module.isa())
+            .expect("value location ranges");
+
+        crate::pretty_clif::write_clif_file(
+            cx.tcx,
+            "opt",
+            instance,
+            &context.func,
+            &clif_comments,
+            Some(&value_ranges),
+        );
+    }
 
     // Define debuginfo for function
     let isa = cx.module.isa();

src/pretty_clif.rs

@@ -74,8 +74,8 @@ pub struct CommentWriter {
 
 impl CommentWriter {
     pub fn new<'tcx>(tcx: TyCtxt<'tcx>, instance: Instance<'tcx>) -> Self {
-        CommentWriter {
-            global_comments: vec![
+        let mut global_comments = if cfg!(debug_assertions) {
+            vec![
                 format!("symbol {}", tcx.symbol_name(instance).name.as_str()),
                 format!("instance {:?}", instance),
                 format!(
@@ -86,7 +86,13 @@ impl CommentWriter {
                     )
                 ),
                 String::new(),
-            ],
+            ]
+        } else {
+            vec![]
+        };
+
+        CommentWriter {
+            global_comments,
             entity_comments: HashMap::new(),
             inst_comments: HashMap::new(),
         }