Merge of #705: Add optimize(size) to some particularly large functions

* Check `as-if-std` only on nightly
* Add `optimize(size)` to some particularly large functions

It saves a few kb in hello world binaries when built as part of libstd.

The comments are formatted like they are so that if this feature
is stabilized they can be identified and used unconditionally.

Author: workingjubilee

.github/workflows/main.yml

@@ -137,8 +137,11 @@ jobs:
 
       # Test that including as a submodule will still work, both with and without
       # the `backtrace` feature enabled.
+      # Building as if part of std requires nightly features to be available
       - run: cargo build --manifest-path crates/as-if-std/Cargo.toml
+        if: matrix.rust == 'nightly'
       - run: cargo build --manifest-path crates/as-if-std/Cargo.toml --no-default-features
+        if: matrix.rust == 'nightly'
 
   windows_arm64:
     name: Windows AArch64

ci/run.sh

@@ -3,4 +3,6 @@
 set -ex
 
 cargo test --target $TARGET
-cargo build --target $TARGET --manifest-path crates/as-if-std/Cargo.toml
+if rustc --version | grep nightly; then
+    cargo build --target $TARGET --manifest-path crates/as-if-std/Cargo.toml
+fi

crates/as-if-std/src/lib.rs

@@ -2,7 +2,7 @@
 // submodule into the standard library. We try to set this crate up similarly
 // to the standard library itself to minimize the likelihood of issues when
 // updating the `backtrace` crate.
-
+#![feature(optimize_attribute)]
 #![no_std]
 
 extern crate alloc;

src/symbolize/gimli.rs

@@ -115,6 +115,8 @@ struct Context<'a> {
 }
 
 impl<'data> Context<'data> {
+    // #[feature(optimize_attr)] is enabled when we're built inside libstd
+    #[cfg_attr(backtrace_in_libstd, optimize(size))]
     fn new(
         stash: &'data Stash,
         object: Object<'data>,
@@ -356,6 +358,8 @@ impl Cache {
     }
 
     // unsafe because this is required to be externally synchronized
+    // #[feature(optimize_attr)] is enabled when we're built inside libstd
+    #[cfg_attr(backtrace_in_libstd, optimize(size))]
     unsafe fn with_global(f: impl FnOnce(&mut Self)) {
         // A very small, very simple LRU cache for debug info mappings.
         //