Auto merge of #55641 - nagisa:optimize-attr, r=pnkfelix

Implement optimize(size) and optimize(speed) attributes

This PR implements both `optimize(size)` and `optimize(speed)` attributes.

While the functionality itself works fine now, this PR is not yet complete: the code might be messy in places and, most importantly, the compiletest must be improved with functionality to run tests with custom optimization levels. Otherwise the new attribute cannot be tested properly. Oh, and not all of the RFC is implemented – attribute propagation is not implemented for example.

# TODO

* [x] Improve compiletest so that tests can be written;
* [x] Assign a proper error number (E9999 currently, no idea how to allocate a number properly);
* [ ] Perhaps reduce the duplication in LLVM attribute assignment code…

3 files changed, 18 insertions, 2 deletions

diff --git a/src/libsyntax/attr/builtin.rs b/src/libsyntax/attr/builtin.rs
index 15e480496f7..1a4b45e76b4 100644
--- a/src/libsyntax/attr/builtin.rs
+++ b/src/libsyntax/attr/builtin.rs
@@ -63,6 +63,13 @@ pub enum InlineAttr {
     Never,
 }
 
+#[derive(Copy, Clone, Hash, PartialEq, RustcEncodable, RustcDecodable)]
+pub enum OptimizeAttr {
+    None,
+    Speed,
+    Size,
+}
+
 #[derive(Copy, Clone, PartialEq)]
 pub enum UnwindAttr {
     Allowed,
diff --git a/src/libsyntax/attr/mod.rs b/src/libsyntax/attr/mod.rs
index e5ce6a3f19a..58be7c3e085 100644
--- a/src/libsyntax/attr/mod.rs
+++ b/src/libsyntax/attr/mod.rs
@@ -4,8 +4,8 @@ mod builtin;
 
 pub use self::builtin::{
     cfg_matches, contains_feature_attr, eval_condition, find_crate_name, find_deprecation,
-    find_repr_attrs, find_stability, find_unwind_attr, Deprecation, InlineAttr, IntType, ReprAttr,
-    RustcDeprecation, Stability, StabilityLevel, UnwindAttr,
+    find_repr_attrs, find_stability, find_unwind_attr, Deprecation, InlineAttr, OptimizeAttr,
+    IntType, ReprAttr, RustcDeprecation, Stability, StabilityLevel, UnwindAttr,
 };
 pub use self::IntType::*;
 pub use self::ReprAttr::*;
diff --git a/src/libsyntax/feature_gate.rs b/src/libsyntax/feature_gate.rs
index 85e80f7bdaf..d74a0d5623a 100644
--- a/src/libsyntax/feature_gate.rs
+++ b/src/libsyntax/feature_gate.rs
@@ -461,6 +461,9 @@ declare_features! (
 
     // Re-Rebalance coherence
     (active, re_rebalance_coherence, "1.32.0", Some(55437), None),
+
+    // #[optimize(X)]
+    (active, optimize_attribute, "1.34.0", Some(54882), None),
 );
 
 declare_features! (
@@ -1222,6 +1225,12 @@ pub const BUILTIN_ATTRIBUTES: &[(&str, AttributeType, AttributeTemplate, Attribu
                            "#[alloc_error_handler] is an unstable feature",
                            cfg_fn!(alloc_error_handler))),
 
+    // RFC 2412
+    ("optimize", Whitelisted, template!(List: "size|speed"), Gated(Stability::Unstable,
+                               "optimize_attribute",
+                               "#[optimize] attribute is an unstable feature",
+                               cfg_fn!(optimize_attribute))),
+
     // Crate level attributes
     ("crate_name", CrateLevel, template!(NameValueStr: "name"), Ungated),
     ("crate_type", CrateLevel, template!(NameValueStr: "bin|lib|..."), Ungated),