ZJIT: Add --zjit-max-versions option (ruby#16607)

Allow configuring the maximum number of compiled versions per ISEQ
via --zjit-max-versions=num (default: 2). Like YJIT's equivalent,
this option is hidden from --help output.

Author: k0kubun

zjit/src/codegen.rs

@@ -26,8 +26,15 @@ use crate::hir_type::{types, Type};
 use crate::options::{get_option, PerfMap};
 use crate::cast::IntoUsize;
 
-/// At the moment, we support recompiling each ISEQ only once.
-pub const MAX_ISEQ_VERSIONS: usize = 2;
+/// Default maximum number of compiled versions per ISEQ.
+const DEFAULT_MAX_VERSIONS: usize = 2;
+
+/// Maximum number of compiled versions per ISEQ.
+/// Configurable via --zjit-max-versions (default: 2).
+pub fn max_iseq_versions() -> usize {
+    unsafe { crate::options::OPTIONS.as_ref() }
+        .map_or(DEFAULT_MAX_VERSIONS, |opts| opts.max_versions)
+}
 
 /// Sentinel program counter stored in C frames when runtime checks are enabled.
 const PC_POISON: Option<*const VALUE> = if cfg!(feature = "runtime_checks") {
@@ -216,7 +223,7 @@ fn gen_iseq_entry_point(cb: &mut CodeBlock, iseq: IseqPtr, jit_exception: bool)
 pub fn invalidate_iseq_version(cb: &mut CodeBlock, iseq: IseqPtr, version: &mut IseqVersionRef) {
     let payload = get_or_create_iseq_payload(iseq);
     if unsafe { version.as_ref() }.status != IseqStatus::Invalidated
-        && payload.versions.len() < MAX_ISEQ_VERSIONS
+        && payload.versions.len() < max_iseq_versions()
     {
         unsafe { version.as_mut() }.status = IseqStatus::Invalidated;
         unsafe { rb_iseq_reset_jit_func(iseq) };
@@ -300,8 +307,8 @@ fn gen_iseq(cb: &mut CodeBlock, iseq: IseqPtr, function: Option<&Function>) -> R
         Some(IseqStatus::CantCompile(err)) => return Err(err.clone()),
         _ => {},
     }
-    // If the ISEQ already hax MAX_ISEQ_VERSIONS, do not compile a new version.
-    if payload.versions.len() == MAX_ISEQ_VERSIONS {
+    // If the ISEQ already has max versions, do not compile a new version.
+    if payload.versions.len() >= max_iseq_versions() {
         return Err(CompileError::IseqVersionLimitReached);
     }
 

zjit/src/codegen_tests.rs

@@ -3,7 +3,7 @@
 use super::{gen_insn, JITState};
 use crate::asm::CodeBlock;
 use crate::backend::lir::Assembler;
-use crate::codegen::MAX_ISEQ_VERSIONS;
+use crate::codegen::max_iseq_versions;
 use crate::cruby::*;
 use crate::hir::{Insn, iseq_to_hir};
 use crate::options::{rb_zjit_prepare_options, set_call_threshold};
@@ -4937,13 +4937,14 @@ fn test_invokesuper_with_local_written_by_blockiseq() {
 
 #[test]
 fn test_max_iseq_versions() {
+    let max_versions = max_iseq_versions();
     eval(&format!("
         TEST = -1
         def test = TEST
 
         # compile and invalidate MAX+1 times
         i = 0
-        while i < {MAX_ISEQ_VERSIONS} + 1
+        while i < {max_versions} + 1
           test; test # compile a version
 
           Object.send(:remove_const, :TEST)
@@ -4956,7 +4957,7 @@ fn test_max_iseq_versions() {
     // It should not exceed MAX_ISEQ_VERSIONS
     let iseq = get_method_iseq("self", "test");
     let payload = get_or_create_iseq_payload(iseq);
-    assert_eq!(payload.versions.len(), MAX_ISEQ_VERSIONS);
+    assert_eq!(payload.versions.len(), max_iseq_versions());
 
     // The last call should not discard the JIT code
     assert!(matches!(unsafe { payload.versions.last().unwrap().as_ref() }.status, IseqStatus::Compiled(_)));

zjit/src/hir.rs

@@ -5129,7 +5129,7 @@ impl Function {
         // SideExits would just add overhead (the exit fires every time without benefit).
         // Keep them as Send fallbacks so the interpreter handles them directly.
         let payload = get_or_create_iseq_payload(self.iseq);
-        if payload.versions.len() + 1 >= crate::codegen::MAX_ISEQ_VERSIONS {
+        if payload.versions.len() + 1 >= crate::codegen::max_iseq_versions() {
             return;
         }
         for block in self.rpo() {

zjit/src/options.rs

@@ -105,6 +105,9 @@ pub struct Options {
 
     /// Path to a file where compiled ISEQs will be saved.
     pub log_compiled_iseqs: Option<std::path::PathBuf>,
+
+    /// Maximum number of versions per ISEQ
+    pub max_versions: usize,
 }
 
 impl Default for Options {
@@ -130,6 +133,7 @@ impl Default for Options {
             perf: None,
             allowed_iseqs: None,
             log_compiled_iseqs: None,
+            max_versions: 2,
         }
     }
 }
@@ -340,6 +344,10 @@ fn parse_option(str_ptr: *const std::os::raw::c_char) -> Option<()> {
             Err(_) => return None,
         },
 
+        ("max-versions", _) => match opt_val.parse() {
+            Ok(n) => options.max_versions = n,
+            Err(_) => return None,
+        },
 
         ("stats-quiet", _) => {
             options.stats = true;