YJIT: Use a boxed slice for gc_obj_offsets (#7397)

* YJIT: Use a boxed slice for gc_obj_offsets

* YJIT: Stop using Option

* YJIT: s/add_counter/incr_counter_by/

Co-authored-by: Maxime Chevalier-Boisvert <maxime.chevalierboisvert@shopify.com>

3 files changed, 24 insertions, 11 deletions

diff --git a/yjit/src/codegen.rs b/yjit/src/codegen.rs
index aac6dab18c..2f41439a41 100644
--- a/yjit/src/codegen.rs
+++ b/yjit/src/codegen.rs
@@ -831,7 +831,7 @@ pub fn gen_single_block(
         let gc_offsets = asm.compile(cb);
 
         // Add the GC offsets to the block
-        block.add_gc_obj_offsets(gc_offsets);
+        block.set_gc_obj_offsets(gc_offsets);
 
         // Mark the end position of the block
         block.set_end_addr(cb.get_write_ptr());
diff --git a/yjit/src/core.rs b/yjit/src/core.rs
index e296afc4da..cd10bd0f04 100644
--- a/yjit/src/core.rs
+++ b/yjit/src/core.rs
@@ -544,7 +544,7 @@ pub struct Block {
 
     // FIXME: should these be code pointers instead?
     // Offsets for GC managed objects in the mainline code block
-    gc_obj_offsets: Vec<u32>,
+    gc_obj_offsets: Box<[u32]>,
 
     // CME dependencies of this block, to help to remove all pointers to this
     // block in the system.
@@ -796,7 +796,7 @@ pub extern "C" fn rb_yjit_iseq_mark(payload: *mut c_void) {
             }
 
             // Walk over references to objects in generated code.
-            for offset in &block.gc_obj_offsets {
+            for offset in block.gc_obj_offsets.iter() {
                 let value_address: *const u8 = cb.get_ptr(offset.as_usize()).raw_ptr();
                 // Creating an unaligned pointer is well defined unlike in C.
                 let value_address = value_address as *const VALUE;
@@ -843,7 +843,7 @@ pub extern "C" fn rb_yjit_iseq_update_references(payload: *mut c_void) {
             }
 
             // Walk over references to objects in generated code.
-            for offset in &block.gc_obj_offsets {
+            for offset in block.gc_obj_offsets.iter() {
                 let offset_to_value = offset.as_usize();
                 let value_code_ptr = cb.get_ptr(offset_to_value);
                 let value_ptr: *const u8 = value_code_ptr.raw_ptr();
@@ -1043,7 +1043,7 @@ fn add_block_version(blockref: &BlockRef, cb: &CodeBlock) {
     }
 
     // Run write barriers for all objects in generated code.
-    for offset in &block.gc_obj_offsets {
+    for offset in block.gc_obj_offsets.iter() {
         let value_address: *const u8 = cb.get_ptr(offset.as_usize()).raw_ptr();
         // Creating an unaligned pointer is well defined unlike in C.
         let value_address: *const VALUE = value_address.cast();
@@ -1088,7 +1088,7 @@ impl Block {
             end_addr: None,
             incoming: Vec::new(),
             outgoing: Vec::new(),
-            gc_obj_offsets: Vec::new(),
+            gc_obj_offsets: Box::new([]),
             cme_dependencies: Vec::new(),
             entry_exit: None,
         };
@@ -1147,12 +1147,12 @@ impl Block {
         self.end_idx = end_idx;
     }
 
-    pub fn add_gc_obj_offsets(self: &mut Block, gc_offsets: Vec<u32>) {
-        for offset in gc_offsets {
-            self.gc_obj_offsets.push(offset);
-            incr_counter!(num_gc_obj_refs);
+    pub fn set_gc_obj_offsets(self: &mut Block, gc_offsets: Vec<u32>) {
+        assert_eq!(self.gc_obj_offsets.len(), 0);
+        if !gc_offsets.is_empty() {
+            incr_counter_by!(num_gc_obj_refs, gc_offsets.len());
+            self.gc_obj_offsets = gc_offsets.into_boxed_slice();
         }
-        self.gc_obj_offsets.shrink_to_fit();
     }
 
     /// Instantiate a new CmeDependency struct and add it to the list of
diff --git a/yjit/src/stats.rs b/yjit/src/stats.rs
index 05e970702c..5d32f613c8 100644
--- a/yjit/src/stats.rs
+++ b/yjit/src/stats.rs
@@ -141,6 +141,19 @@ macro_rules! make_counters {
     }
 }
 
+/// Macro to increase a counter by name and count
+macro_rules! incr_counter_by {
+    // Unsafe is ok here because options are initialized
+    // once before any Ruby code executes
+    ($counter_name:ident, $count:expr) => {
+        #[allow(unused_unsafe)]
+        {
+            unsafe { $crate::stats::COUNTERS.$counter_name += $count as u64 }
+        }
+    };
+}
+pub(crate) use incr_counter_by;
+
 /// Macro to increment a counter by name
 macro_rules! incr_counter {
     // Unsafe is ok here because options are initialized