ZJIT: Track guard shape exit ratio (#15052)

new ZJIT stats excerpt from liquid-runtime: 
```
    vm_read_from_parent_iseq_local_count:        10,909,753
    guard_type_count:                            45,109,441
    guard_type_exit_ratio:                             4.3%
    guard_shape_count:                           15,272,133
    guard_shape_exit_ratio:                           20.1%
    code_region_bytes:                            3,899,392
```

lobsters
```
guard_type_count:                            71,765,580
guard_type_exit_ratio:                             4.3%
guard_shape_count:                           21,872,560
guard_shape_exit_ratio:                            8.0%
```

railsbench
```
guard_type_count:                            117,661,124
guard_type_exit_ratio:                              0.7%
guard_shape_count:                            28,032,665
guard_shape_exit_ratio:                             5.1%
```

shipit
```
guard_type_count:                            106,195,615
guard_type_exit_ratio:                              3.5%
guard_shape_count:                            33,672,673
guard_shape_exit_ratio:                            10.1%
```

3 files changed, 6 insertions, 1 deletions

diff --git a/zjit.rb b/zjit.rb
index cfe8bcd6e2..5156c72f43 100644
--- a/zjit.rb
+++ b/zjit.rb
@@ -152,6 +152,7 @@ class << RubyVM::ZJIT
     stats = self.stats
 
     stats[:guard_type_exit_ratio] = stats[:exit_guard_type_failure].to_f / stats[:guard_type_count] * 100
+    stats[:guard_shape_exit_ratio] = stats[:exit_guard_shape_failure].to_f / stats[:guard_shape_count] * 100
 
     # Show counters independent from exit_* or dynamic_send_*
     print_counters_with_prefix(prefix: 'not_inlined_cfuncs_', prompt: 'not inlined C methods', buf:, stats:, limit: 20)
@@ -206,6 +207,8 @@ class << RubyVM::ZJIT
 
       :guard_type_count,
       :guard_type_exit_ratio,
+      :guard_shape_count,
+      :guard_shape_exit_ratio,
 
       :code_region_bytes,
       :side_exit_count,
@@ -242,7 +245,7 @@ class << RubyVM::ZJIT
       case key
       when :ratio_in_zjit
         value = '%0.1f%%' % value
-      when :guard_type_exit_ratio
+      when :guard_type_exit_ratio, :guard_shape_exit_ratio
         value = '%0.1f%%' % value
       when /_time_ns\z/
         key = key.to_s.sub(/_time_ns\z/, '_time')
diff --git a/zjit/src/codegen.rs b/zjit/src/codegen.rs
index 01212ac88c..364b9225fe 100644
--- a/zjit/src/codegen.rs
+++ b/zjit/src/codegen.rs
@@ -964,6 +964,7 @@ fn gen_array_extend(jit: &mut JITState, asm: &mut Assembler, left: Opnd, right:
 }
 
 fn gen_guard_shape(jit: &mut JITState, asm: &mut Assembler, val: Opnd, shape: ShapeId, state: &FrameState) -> Opnd {
+    gen_incr_counter(asm, Counter::guard_shape_count);
     let shape_id_offset = unsafe { rb_shape_id_offset() };
     let val = asm.load(val);
     let shape_opnd = Opnd::mem(SHAPE_ID_NUM_BITS as u8, val, shape_id_offset);
diff --git a/zjit/src/stats.rs b/zjit/src/stats.rs
index 30a0966994..aea28db28b 100644
--- a/zjit/src/stats.rs
+++ b/zjit/src/stats.rs
@@ -286,6 +286,7 @@ make_counters! {
 
     // The number of times we ran a dynamic check
     guard_type_count,
+    guard_shape_count,
 }
 
 /// Increase a counter by a specified amount